deliverable d4.1 report of different options for renewable ...figure 4-2 annual sum of global...

Deliverable D4.1

Report of different options for renewable energy supply

in Data Centres in Europe

Authors:

Oriol Gavaldà (Aiguasol), Victor Depoorter (IREC), Thomas Oppelt (TUC), Karl van Ginderdeuren (Deerns)

The project Advanced concepts and tools for

renewable energy supply of IT Data Centres is

co-funded by the European Union

Project acronym RenewIT

Project number FP7 – SMARTCITIES – 2013 – 608679

Project title Advanced concepts and tools for renewable

energy supply of IT Data Centres

Website www.renewit-project.eu

Deliverable D4.1

Title of deliverable Report of different options for renewable energy supply

in Data Centres in Europe

Workpackage WP4

Dissemination level Public

Data of deliverable 12/02/2014

Authors Oriol Gavaldà (Aiguasol), Victor Depoorter (IREC),

Thomas Oppelt (TUC), Karl van Ginderdeuren (Deerns)

Contributors Jaume Salom (IREC), Eduard Oró (IREC), Oscar Càmara

(Aiguasol), Thorsten Urbaneck (TUC), Noah Pflugradt

(TUC), Bianca van der Ha (Deerns)

Reviewers Davide Nardi Cesarini (AEA)

This deliverable contains original unpublished work except where clearly

indicated otherwise. Acknowledgement of previously published material and of

the work of others has been made through appropriate citation, quotation or

both.

http://www.renewit-project.eu/

Version Date Author Organisation Comments

0.1 13/01/2014 Oriol Gavaldà AIGUASOL First version, pending

DEERNS chapters

0.2 14/01/2014 Oriol Gavaldà AIGUASOL Small corrections in

executive summary. New

graph

1 07/02/2014 Oriol Gavaldà AIGUASOL Corrections of all partners

including reviewer

2 12/02/2014 Oriol Gavaldà AIGUASOL Final version

Advanced concepts and tools for renewable energy supply of IT Data Centres

RenewIT - Project number: 608679

D4.1 Report of different options for renewable energy supply in Data Centres in Europe

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TABLE OF CONTENTS Table of Contents ....................................................................................... 5

Table of Tables .......................................................................................... 8

Table of Figures ......................................................................................... 9

Keywords ................................................................................................ 13

List of abbreviations ................................................................................. 14

Executive summary .................................................................................. 16

1 Introduction ..................................................................................... 18

2 Background ...................................................................................... 19

2.1 General concepts of renewable energies in Data Centres ................... 19

2.2 Types of renewable energy supply for Data Centres .......................... 20

2.2.1 Own renewable energy supply 22

2.2.2 Renewable energy supply from a third-party 24

3 Global indicators about the electricity mix in Europe .............................. 26

3.1 Description and assessment of the energy indicators ........................ 26

3.1.1 Electricity generated from renewable energy sources 26

3.1.2 Primary energy factor 28

3.1.3 CO2 emissions factor 29

3.1.4 Energy dependency rate 30

3.1.5 Day-ahead spot price of electricity 33

3.2 Hourly basis assessment of the global indicators .............................. 34

3.3 Development of electrical mix indicators in the future ....................... 37

4 Availability of renewable energy resources in Europe ............................. 41

4.1 Renewable energy resources ......................................................... 41

4.2 Survey of renewable energy resources in Europe ............................. 42

4.2.1 Solar energy 42

4.2.2 Wind energy 43

4.2.3 Biomass energy 44

4.2.4 Geothermal energy 46

4.2.5 Marine energy 47

4.2.6 Environmental energy 49

4.3 Survey of renewable energy resources in sample countries ............... 51


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4.4 Analysis of Data Centre space availability ........................................ 54

5 Technology analysis of renewable energy technologies .......................... 56

5.1 Introduction ................................................................................ 56

5.2 Current energy consumption of data centres.................................... 57

5.2.1 Technical characteristics of data centres HVAC systems 58

5.3 Renewable Energy technologies for power supply ............................. 61

5.3.1 Generation 62

5.3.1.1 Solar photovoltaic 62

5.3.1.2 Wind energy 64

5.3.1.3 Hydro energy 66

5.3.1.4 Ocean mechanical energy technologies 67

5.3.1.5 Summary of power-only generation through renewable energy

resources 69

5.3.2 Electric accumulation 70

5.3.3 Conversion 74

5.3.3.1 Ground source or natural water source heat pumps 74

5.4 Renewable energy technologies for low-enthalpy heat generation ...... 76

5.4.1 Introduction 76

5.4.2 Generation 77

5.4.2.1 Solar thermal collectors 77

5.4.2.2 RE boilers (biomass, biogas, syngas, biodiesel) 81

5.4.2.3 Geothermal low-enthalpy sources 82

5.4.3 Conversion into cooling 83

5.4.4 Storage 86

5.4.4.1 Heat storage 86

5.4.4.2 Cold storage 89

5.5 Renewable energy technologies for high enthalpy heat generation ..... 92

5.5.1 Generation 92

5.5.1.1 Solar thermal power 92

5.5.1.2 Medium and high enthalpy geothermal systems 95

5.5.1.3 Biomass thermal power 96



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5.5.1.4 Summary of high-enthalpy thermal generation technologies 97

5.5.2 Conversion to electricity 98

5.5.2.1 Gas turbines 98

5.5.2.2 Microturbines 98

5.5.2.3 Externally fired gas turbines gas turbines 99

5.5.2.4 Steam Rankine turbines 99

5.5.2.5 Stirling engines (for solar thermal and biomass) 99

5.5.2.6 Organic Rankine Cycle Turbines 101

5.5.2.7 Internal Combustion Engines (ICE) 102

5.5.2.8 Fuel cells 103

5.5.2.9 Combined cycle 103

5.5.3 Storage 105

6 Potential of on-site renewable energy systems ..................................... 106

6.1 Introduction ............................................................................... 106

6.2 Analysed schemes ....................................................................... 108

6.3 Consumption of an Data Centre reference case ............................... 109

6.4 Results of on-site energy production for example data centre ........... 110

6.4.1 Methodology and indicators 110

6.4.2 Results 110

6.5 First recommendations and partial conclusions ................................ 112

7 Examples of existing Data Centres with renewable energy ..................... 113

7.1 Introduction ............................................................................... 113

7.2 Concrete examples of Data Centres ............................................... 116

7.3 Various other use of renewables within data centres ........................ 123

8 Conclusions ..................................................................................... 125

9 References ...................................................................................... 126

Annex 1. Detailed renewable energy resource data analysis for different locations136

Spain 137

Germany 142

Netherlands 148

Sweden 153



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TABLE OF TABLES

Table 3.1 Comparison between EDRs in 2012 considering nuclear as imported or

indigenous primary energy 32

Table 3.2 CO2 EFs for EU electricity grid in 2010 and 2050 in gCO2/kWhf [31] 39

Table 4.1 Reference locations 52

Table 4.2 Renewable energy resources in the sample countries [34] 53

Table 5.1 Data Centre space structure 57

Table 5.2 Overview on HVAC systems for Data Centre cooling 60

Table 5.3 Summary of power only generation through renewable energy

resources 69

Table 5.4 Summary table for electrical accumulation [63] 73

Table 5.5 Basic data of biofuels 82

Table 5.6 Summary table for closed cycle cooling [72] 84

Table 5.7 Summary table for open cycle cooling [72] 85

Table 5.8 Summary for high-enthalpy thermal generation technologies 97

Table 5.9 Summary of electricity conversion technologies 104

Table 6.1 Consumption in a typical Data Centre 109

Table 6.2 General rough numbers on required power and space for several

configurations 111

Table 7.1 Overview of Examples of Applied Renewables in Data Centres 115



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TABLE OF FIGURES

Figure 2-1 Overview of possible renewable supply options for Data Centres 22

Figure 2-2 Power Purchase Agreements [13] 25

Figure 3-1 Profile of the RES-E in year 2012 27

Figure 3-2 Grid primary energy factor in 2012 29

Figure 3-3 Grid CO2 emission factor in 2012 30

Figure 3-4 Energy dependency rate in 2012 (indigenous nuclear) 32

Figure 3-5 Example of retail price components for small industrial consumers of

5GWh in several European regions [28] 33

Figure 3-6 Day-ahead spot prices of electricity in 2012 34

Figure 3-7 Daily profiles of the share of RES in the Spanish electricity mix 35

Figure 3-8 Daily profiles of the global PEF of the Spanish electricity mix 36

Figure 3-9 Daily profiles of the global CO2 EF of the Spanish electricity mix 36

Figure 3-10 Daily profiles of the EDR of the Spanish electricity mix 37

Figure 3-11 Daily profiles of the day-ahead spot price of electricity in Spain 37

Figure 3-12 Correlation between the electricity mix indicators for Spain 38

Figure 3-13 Development of the share of RES-E in the different scenarios [31] 39

Figure 3-14 Development of the PEF in different countries up to 2050 [19] 40

Figure 4-1 Primary energy resources, usable energy carriers and evaluated

renewable energy resources 41

Figure 4-2 Annual sum of global horizontal radiation in Europe [35] 42

Figure 4-3 Wind power potentials in Europe (km/s⋅km2) [37] 43

Figure 4-4 Distribution of wind energy density in Europe for 2030 [36] 44

Figure 4-5 Available biomass energy potential 2000 [37] 45

Figure 4-6 Available biomass energy potential divided by country area [37] 46

Figure 4-7 Geothermal heat flux in Europe [40] 47

Figure 4-8 Mean tidal amplitude at European coasts [42] 48

Figure 4-9 Wave power levels in kW/m of crest length in European waters [44] 49

Figure 4-10 Sea surface temperatures measured in January 2012 [47] 50

Figure 4-11 Sea surface temperatures measured in July 2012 [45] 51

Figure 4-12 Sample countries and reference locations [47] 52



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Figure 4-13 Monthly direct radiation for the four locations [47] 53

Figure 4-14 Monthly diffuse radiation for the four locations [47] 54

Figure 5-1 General scheme of the interaction of the different chapters in the

technology analysis 57

Figure 5-2 Overview on HVAC systems for Data Centre cooling 59

Figure 5-3 Conceptual graph of chapter 5.3 61

Figure 5-4 Images of two PV installations (one building integrated and another in

industrial premises) [54] 63

Figure 5-5 Offshore park near Copenhagen [57] 65

Figure 5-6 Two typical designs of a high-flow low head hydro power facility (left)

and a low-flow high-head power facility (right) [57] 66

Figure 5-7 Pelamis wave turbine and SeaGen tidal energy harvesting [62] 67

Figure 5-8 Energy efficiencies of all different electric accumulation technologies 73

Figure 5-9 The three different types of ground source heat pumps [64] 74

Figure 5-10 Conceptual map of the chapter 76

Figure 5-11 Solar thermal flat plate collectors and linear Fresnel collectors [65]

[66] 78

Figure 5-12 Efficiency curves for different collectors and different thermally

driven chillers, for ambient temperatures of 25ºC and radiation 800 W/m2 [67] 79

Figure 5-13 Trends in costs in solar thermal [70] 80

Figure 5-14 Industrial boiler, to be used with hot water, superheated water,

steam [71] 81

Figure 5-15 General graph of conversion of thermal energy into cooling 83

Figure 5-16 Four types of seasonal thermal energy stores [74] 87

Figure 5-17 Specific storage costs of demonstration plants (cost figures without

VAT) [74] 88

Figure 5-18 Example of solar dish with a stirling engine [75] 93

Figure 5-19 Image of Parabolic Through Concentrator [75] 94

Figure 5-20 Image of a small tower system. [77] 94

Figure 5-21 Example of geothermal harvesting Rankine cycle. Sizes between 2

and 45 MWel [78] 95

Figure 5-22 Stirling engine and Stirling cycle 100



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Figure 5-23 Efficiency of a Solar stirling system [75] 101

Figure 5-24 ORC from Turboden, installed in Burgos [83] 101

Figure 6-1 General strategies for use of renewable energies in Data Centres 107

Figure 6-2 Different pieces of the puzzle, that have to be combined to be able to

compound the systems 108

Figure 6-3 Division between consumption requirements 109

Figure 7-1 KPN data centre, Haarlem 116

Figure 7-2 Google data centre in Hamina, Finland [85] 117

Figure 7-3 Rabobank data centre Boxtel 117

Figure 7-4 T-Systems Data Centre in Magdenburg 118

Figure 7-5 University Medical Centre Groningen 118

Figure 7-6 University Utrecht 119

Figure 7-7 Equinix data centre Amsterdam 120

Figure 7-8 Facebook Luleå 121

Figure 7-9 Facebook Altoona 121

Figure 7-10 Rabobank, Best 122

Figure 7-11 Facebook Prineville 123

Figure 7-12 Telecity Data Centre West London, UK 123

Figure A0-1 Sun chart for Barcelona, Spain 137

Figure A0-2 Availability of solar energy in Barcelona [97] 138

Figure A0-3 Availability of wind energy (wind speed at 10 m above ground) in

Barcelona, Spain [97] 139

Figure A0-4 Spanish biomass energy resources in 2000 (total: 120 TWh) [37]140

Figure A0-5 Availability of ambient air for free cooling in Barcelona, Spain [97]141

Figure A0-6 Availability of solar energy in Chemnitz, Germany [97] 143

Figure A0-7 Sun chart for Chemnitz, Germany 144

Figure A0-8 German biomass energy resources in 2000 [37] 144

Figure A0-9 Availability of wind (wind speed at 10 m above ground )energy in

Chemnitz, Germany [97] 145

Figure A0-10 Geothermal resources in Germany [100] 146

Figure A0-11 Availability of ambient air for free cooling in Chemnitz, Germany

[97] 147

Figure A0-12 Availability of solar energy in Amsterdam, Netherlands [97] 149



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Figure A0-13 Sun chart for Amsterdam, Netherlands 150

Figure A0-14 Dutch biomass energy resources in 2000 (total: 33 TWh) [37] 150

Figure A0-15 Availability of wind (wind speed at 10 m) energy in Amsterdam,

Netherlands [97] 151

Figure A0-16 Geothermal resources in the Netherlands [106] 152

Figure A0-17 Availability of ambient air for free cooling in Amsterdam,

Netherlands [97] 153

Figure A0-18 Availability of solar energy in Luleå, Sweden [97] 155

Figure A0-19 Sun chart for Luleå, Sweden 156

Figure A0-20 Swedish biomass energy resources in 2000 (total: 92 TWh) [37]156

Figure A0-21 Availability of wind (wind speed at 10 m) energy in Luleå, Sweden

[97] 157

Figure A0-22 Availability of ambient air for free cooling in Luleå, Sweden [97] 159



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KEYWORDS

Biomass

Data Centres

Electrical storage

Ocean energy

Renewable energy sources

Solar thermal

State of the art

Thermal storage

Thermally Driven Cooling

Tidal energy

Wind energy



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LIST OF ABBREVIATIONS

ATES Aquifer Thermal Energy Stores

BESS Battery Energy Storage Systems

BIPV Building Integrated Pv

BTES Borehole Thermal Energy Stores

CAES Compressed Air Energy Storage Systems

CHCP Combined Heat, Cooling And Power

CPC Compound Parabolic Concentrator

C-PCS Control And Power Conditioning System

DEC Desiccant Evaporative Cooling

DEMO Demonstration maturity level

DEP Deployment maturity level

DOE Department Of Energy Of The US

EC European Commission

EDR Energy Dependency Rate

EF Emissions Factor

EPBD European Union Directive On Energy Performance Of Buildings

ESS Energy Storage Systems

ETC Evacuated Tube Collector

FESS Flywheel Energy Storage System

FPC Flat Plate Collector

GHP Groundsource Heat Pumps

GO Guarantee Of Origin

HESS Hydrogen Energy Storage System

HTS High Temperature Coils

HVAC Heating, Ventilation And Air Conditioning

ICE Internal Combustion Engines

IDAE Instituto Para La Diversificación Y Ahorro De Energía

IEA International Energy Agency

IT Information Technology



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LHV Lower Heating Value

LTS Low Temperature Coils

MAT Mature Technology

Net ZEDC Net Zero Energy Data Centres

nZEBs Nearly Zero Energy Buildings

ORC Organic Cycle Rankine

OTEC Ocean Thermal Energy Conversion

PCM Phase Change Materials

PEFs Primary Energy Factors

PEM Polymer Electrolyte Membrane

PHS Pumped Hydro Storage

PPA Power Purchase Agreement

PTC Parabolic Through Collector

PUE Power Usage Efficiency

PV Photovoltaic

PVPS Photovoltaic Power Systems Programme

RES Renewable Energy Sources

RES Research maturity level

RES-E Ratio Between The Gross Electricity Production From RES And The Gross National Electricity Consumption

RFC Regenerative Fuel Cell

ROI Return On Investment

SCESS Supercapacitors

SMES Superconducting Management Energy Storage

UPS Uninterruptible Power Supply

UTES Underground Thermal Energy Storage

Wp Watt peak



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EXECUTIVE SUMMARY

The main objective of this document is to study the integration of different

options of renewable power and heat/cold production into Data Centres. In this

framework, several renewable energy solutions have been studied, with a special

focus on large scale systems: solar thermal, solar photovoltaic, wind power,

geothermal, sky radiation, and combined heat and power (CHP) with biomass.

Moreover, an important effort analysing indirect solutions aimed to increase the

renewable electricity mix ratio has also been done.

The focus of the work has been to give the most essential information as far as

renewable energy generation for Data Centres is concerned, as comprehensive

as possible, but with high quality standards.

This deliverable, hence, is a wide overview of existing renewable energy

technologies that could somehow be integrated to Data Centres. Moreover their

efficiency, cost and level of maturity have been studied. Since the duration of the

project is for three years, technologies that nowadays still seem far from market

have been included in this first deliverable. However, next deliverables will focus

more on the technologies that can be applied at this time or in the near future.

An overview of possible renewable supply options for data centres differentiating

between ‘on-site’ and ‘off-site’ generation and mentioning renewable energy

supply from third party (green certificates) has been done. Once the concepts

were established, indicators on the electricity mix of many European countries

have been analysed. This analysis will allow the Data Centre operators to know

the attributes of the electricity they are going to consume in its infrastructures

from the grid. On the other hand, these indicators could be used as decision

variables in algorithms for the management and operation of Data Centres. The

chosen indicators are the share of renewables in the gross electricity production,

the primary energy factor, the CO2 emissions factor, the energy dependency rate

and the day-ahead spot electricity price.

Renewable energy resources for European countries have been studied, with a

special interest on four locations (Spain, Germany, Holland and Sweden) taking

into account different climate locations along Europe: Mediterranean climates,

central European climates, Atlantic European climates and northern European

climates. A detailed analysis of these climates has been included as an annex to

the document.

Once resources were known, the technologies to harvest, convert and

accumulate these resources have been under study. They have been divided into

renewable energy power technologies (for electricity production), low-enthalpy



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thermal renewable energy technologies (for cooling production) and high-

enthalpy thermal renewable energy technologies (for electricity and cooling

production). Moreover, for each technology, each technology principle,

efficiencies, level of maturity, current costs and its estimated future costs has

been analysed.

As a final step, in order to give a first approach at the potential renewable

energy fraction that on-site energy systems can give, a first look at the

maximum production in the different locations has been proposed, based on the

most conventional schemes that have been used up to the moment either in

Data Centres or in conventional buildings with important cooling and power

requirements.

It is important to highlight that one conclusion is that on-site energy production

(wind or solar) has enormous difficulties in being able to cover energy

requirements due to the high energy density of this unique infrastructures.

However, Data Centres with space availability nearby, like airports Data Centres

or other open spaces, might offer interesting options for renewable energy

production on-site. Therefore it is remarkable that an important effort to reduce

the energy demand in Data Centres has to be done to increase the importance of

using renewable energy. On the other hand, on-site generation with off-site

energy (biomass) might offer more options for supplying nearly zero energy Data

Centre.

Finally, interesting examples of existing Data Centres which run with renewable

energy have been detected and described in this document, most of which are

concentrated on improving the efficiency of the cooling system, via heat

dissipation into specific heat sinks (rivers, lakes, etc.) or with energy efficiency

measures as free-cooling or indirect air heat recovery.



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1 INTRODUCTION

This document studies the different options of renewable power or renewable

heat for integration in Data Centres.

Chapter 2 will be used to describe the main concepts of renewable energy supply

applied to Data Centres, and the morphologies of renewable energy integration

to the current energy systems of Data Centres. Moreover, in chapter 3, the

current electricity mix of some European countries will be analysed. This is the

current scenario, and it can allow the Data Centre operators to know the

attributes of the electricity they consume from the grid. On the other hand, these

indicators could be used as decision variables in algorithms for the management

and operation of Data Centres.

After these two background chapters, the document will focus on renewable

energies. Chapter 4 will analyse and study energy resource availability along

Europe. A more detailed analysis on four specific locations in Europe will be

annexed to the document.

Following the resource analysis, the technologies to harvest, convert and

accumulate these resources will be described in chapter 5. Each of the different

technologies will be shortly described, with technical data on their efficiencies

and present and future costs. Chapter 5 focuses on the individual components of

the systems, and afterwards, chapter 6 makes a first approach at the system

concept. Some potential schemes of renewable energy technologies applied to

Data Centres will be studied, in order to give a first approach to the potential.

Some examples of real installations in Data Centres will be showed in chapter 7,

to see real life examples of the aforementioned technologies applied to Data

Centres. Finally, chapter 8 summarises the conclusions of the former chapters

and introduces the following steps in the RenewIT project.



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2 BACKGROUND

2.1 GENERAL CONCEPTS OF RENEWABLE ENERGIES IN DATA CENTRES

RenewIT aims to develop advanced concepts to improve energy efficiency and

renewable energy integration in Data Centres. As a final consequence, maximum

integration of renewables leads to the emerging concept of Net Zero Energy Data

Centres (Net ZEDC). A Net ZEDC can be succinctly described as a grid-connected

Data Centre that generates as much energy as it uses over a year. This

emerging concept has been inspired by the topic of Zero Energy Buildings (ZEBs)

which has received increasing attention in recent years [1], until becoming part

of the energy policy in several countries. In the recast of the EU Directive on

Energy Performance of Buildings (EPBD) [2] it is specified that by the end of

2020 all new buildings shall be “nearly zero energy buildings”. The EPBD recast

defines nearly zero energy buildings (nZEBs) as high performance buildings in

which “the very low amount of energy required should be covered to a very

significant extent by energy from renewable sources, including energy from

renewable sources produced on-site or nearby”. Despite the emphasis on the

goals, there are a lot of on-going efforts to develop a consistent definition and

framework for the evaluation of Net ZEBs [3] [4].

According to the EPBD, the energy from renewable sources is defined as “energy

from renewable non-fossil sources, namely wind, solar, aerothermal, geothermal,

hydrothermal, ocean energy, hydropower, biomass, landfill gas, sewage

treatment plant gas and biogases”. Although some of them are already mature

technologies, the challenge lies now in their integration in Data Centres without

forgetting that, under the concept of Net Zero Energy Data Centres, this should

be the last step after applying savings and energy efficiency measures. To

effectively integrate renewable energy sources (RES) in Data Centres some

issues have to be overcome. On the one hand, the optimal location for Data

Centres does not always have a suitable renewable potential or space availability

for renewable installations. In addition, Data Centres operate uninterrupted for 24 hours a day and 365 days a year while RES don’t. Finally, the high density of

loads and the absence of heating loads are additional difficulties in effectively

cooling the Data Centres.

In the present document, therefore, the use of the term renewable energy will be

more focused. Three main groups of technologies have been excluded from the

term: business as usual technologies, energy efficiency measures and energy

harvesting from non-renewable sources. In the group of business as usual

technologies, though the EPBD directive mentions aerothermal as one of the

renewable energy sources, we have considered the use of the aforementioned

technology as one of the necessary previous steps, same as energy efficiency

measures, like free-cooling and heat/cold recovery in the cases it is possible.



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Energy efficiency measures won’t be explained, and neither will be energy

harvesting technologies, as piezoelectric generation in roads [5], industrial heat

recovery or exportation of low-enthalpy heat.

2.2 TYPES OF RENEWABLE ENERGY SUPPLY FOR DATA CENTRES

In the recent years, major Data Centre operators such as Google or Apple are

pushing towards covering their Data Centre’s power demand using renewable

energy. The sector has realized the significant environmental benefits of using

renewable energy for Data Centres - following techniques such as workload

scheduling, geographical load balancing, etc. However, the companies are

following different strategies in order to make their environmental commitment

visible. In the following section, alternative ways for Data Centres to incorporate

renewable energy into their overall energy portfolio will be described and a

consistent taxonomy referring to published literature will be defined.

Furthering the comparison between Data Centres and Net ZEBs, a definition may

set mandatory requirements on energy supply, including a hierarchy of

renewable energy supply options. The distinction is typically made at least

between ‘on-site’ and ‘off-site’, but for using a hierarchy a clear definition of

options has to be stated according to system boundaries. In 2010, Pless and

Torcellini [6] described different renewable energy supply options prioritized on

the basis of three principles: emissions-free and reduced transportation and

conversion losses; availability over the lifetime of the building; highly scalable,

widely available, and have high replication potential for future Net ZEBs. These

principles lead to a hierarchy of supply options where resources within the

building footprint or on-site were given priority over off-site supply options. Later

on, Marszal et al. [7] did a similar classification which was not intended to be a

hierarchical classification, but a merely graphical representation of the different

energy supply options. Actually, the main difference between both approaches

lay on the meaning of off-site, depending on whether the focus was the origin of

the fuel or the location of the actual generation system. From the regulatory

point of view, the EPBD recast used “nearby” and “on-site” terms in the definition

of nZEBs, but with certainly an ambiguous meaning which was expected to be

clarified by each Member State. On the other hand, the draft of the overarching

standard prEN 15603:2013 [8] distinguishes between “nearby” and “distant”

when refering to energy sources outside the building site. This draft proposes as

“nearby” an energy source “which can be used at local or district level and

requires a specific network and specific equipment for the assessed building to

be connected to it” and discusses if the “specific network should be designed for

the particular building site”. Considering this unclear regulatory framework,

REHVA [9] has provided a new technical definitions and energy calculation



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principles for NZEB in order to assist the implementation of the EPBD recast and

the prEN 15603:2013. According to REHVA, different assessment boundaries

(understood as boundaries where the energy balance of delivered and exported

energy is defined) can be defined depending on whether renewable energy

comes from on-site renewable energy or nearby production contractually linked

to the building which is distributed through the grid or district heating or cooling

network. In this context, “contractually linked to the building” means that new

renewable production capacity is constructed to serve this building. Finally, Ren

et al. developed an optimization framework to evaluate various ways for Data

Centres to incorporate renewable energy to their energy portfolio: on-site

generation, off-site generation feeding into the grid, power purchase agreements

feeding into the grid, and renewable energy certificates [10]. The results showed

that the most cost-effective options for carbon reduction vary depending on

carbon footprint targets, which calls into question the hierarchy in which the

closer resources to the Data Centre always would have priority over the most

distant.

After reviewing the different approaches gathered in the literature, the

consortium proposes the classification shown in Figure 2-1. This approach groups

renewable energy supply options according to whether Data Centre operators

decide to generate their own renewable energy or to buy it to a third through

different legal instruments. These options differ in the ease and cost of

implementation, the need for capital investment, the ability to hedge risk and the

length of time over which Data Centre operators realise the benefits [11].

However, from a policy point of view, the main difference relies on the influence

Data Centre operators have to increase the installed capacity of RES.



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Figure 2-1 Overview of possible renewable supply options for Data Centres

2.2.1 OWN RENEWABLE ENERGY SUPPLY

This is the case of Data Centre operators which generate their own energy,

having a direct control or influence on the energy resource. In any case, new

renewable production capacity is constructed to serve the Data Centre, either

“on-site” or “off-site”. Having new renewable generation capacity typically

requires an up-front investment (as part of either a financed project or a capital

appropriation), but the reduction in the consumption of conventional energy can

last up to 30 years. The two types of own renewable energy supply options are

discussed below:

On-site generation: As shown in chapter 7, Data Centres are installing

renewable energy sources within their own facilities. In on-site

deployments, the generation of usable forms of energy takes place within



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the Data Centre footprint or site (understood as the ground owned by the

Data Centre owner which is directly adjacent to the building footprint). On

site renewable energy includes thermal energy produced by solar

collectors and electrical energy by Photovoltaic (PV) panels, wind or hydro

turbines. The thermal energy extracted from ambient heat sources by heat

pumps is also on site renewable energy and the ambient heat exchangers

may be treated as renewable energy generators in the renewable energy

calculation. However, renewable fuels such as biomass are not included in

on site renewables, but they are renewable part of the delivered energy.

In this sense, a distinction can be made between:

o On-site generation from on-site renewables: the RES is directly

available in the site.

o On-site generation from off-site renewables: the RES has to be

supplied from outside the building site but the generation of usable

forms of energy takes place on the project site, i.e. energy carriers

need to be transported, as biomass or biogas.

In any case, dependence on the generators or the grid and the district

heating or cooling networks is lowered, although Data Centres normally

require storage systems or network ties for when renewable energy is not

available. A plus for on-site deployments is that, since the power

undergoes fewer conversions and is not transmitted over long distances,

incur much lower losses are incurred. Unfortunately, this approach has

also drawbacks. It could occur that the optimal location of a Data Centre

(subject to factors such as network latencies, labour force availability, tax

structures, etc.) does not match with the places with the best renewable

power potentials.

Off-site generation: When the conditions for on-site renewable

generation (related to renewable energy potential, space availability,

centralized network connection, etc.) are not suitable, an off-site location

may be preferable. In this approach, the Data Centre operator makes a

long term investment in a renewable energy plant at locations with

abundance of the renewable resource or in a community system. The grid

or the heating/cooling network essentially acts as the “carrier” of the

produced energy. Of course, the transportation leads to energy losses

which shall be assessed in the energy performance calculations of the Data

Centre, but which could be compensated by improving the plant’s capacity

factor. At this point, the difference between the centralized electricity grid

and cooling/heating networks should be considered. While power systems

are normally large-scale and spread out infrastructures which could

reasonably well absorb the added capacity, heating/cooling networks are

local-scaled structures with limited capacity to absorb new inputs. Another

distinction has to be made between cases when a specific network is

constructed between the generation site and the Data Centre and cases



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when energy transmission is done through already available general

infrastructures by incurring transmission charges. Generally, the latter

option requires the availability of legislation allowing to connect new

renewable generation capacity to the Data Centre building and establishing

mechanisms which allow recording the energy contributed by the off-site

source to the grid and incorporating this into the bill of the Data Centre

operator. In any case, Data Centre is dependent on the availability of the

transmission medium.

2.2.2 RENEWABLE ENERGY SUPPLY FROM A THIRD-PARTY

Another strategy which is already being used by Data Centre operators is to buy

renewable energy generated from other entities. Therefore, in this case the Data

Centre is not an active participant in the provisioning and operation of the energy

source. Nowadays Data Centre operators can choose between numerous ways to

incorporate renewable energy into their overall energy consumption portfolio.

The most important mechanisms are electricity tracking certificates and

renewable electricity products, which usually require no up-front capital and are

relatively easy to procure.

Electricity Tracking Certificates: Certificates normally refer to the

vehicle used to carry certified electricity attributes via an electricity

tracking system. Electricity attributes are factual information (e.g. grams

of CO2/kWh, electricity production source, land of the produced electricity

etc.) that can be gained through the cancelation of a reliable tracking

certificate and which allows the end-user to claim the type of electricity

they used --as well as other factual information based on the origins-- of

the electricity certificate they cancelled. This means that these certificates

only prove that one MWh of electricity with the specified attributes was

produced. Certificates are tradable commodities in certificates markets and

are sold separately from the underlying physical electricity. In Europe, the

primary certificate used is the Guarantee of Origin or GO (in other

locations like the United States the certificate used is the Renewable

Energy Certificate or REC). The GO is regulated in the European Directive

2009/28/EC (known as the “The Renewables Directive”) and is further

standardized via the European Energy Certificate System provided by the

Association of Issuing Bodies. This organism makes trade, cancelation and

use of GOs standardized across Europe, making all forms of double

counting, attributing and claiming impossible [12].

Renewable energy products: Data Centres may choose to buy their

desired mix of green and brown energy from their electricity provider or a

third party provider. A renewable product can be in terms of fixed green



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energy quantity or a blended green and brown energy with certain

percentage of green guaranteed. Another type of renewable energy

product is the Power Purchase Agreement (PPA). A PPA is a contract

between a purchaser and a supplier which lays out how much electricity

the supplier has promised to place on the grid and how much the

consumer will take off. A PPA most often guarantees an electricity price

beyond just guaranteeing the supply. A PPA however can never deliver

electricity attributes that are different from the grid-average unless

tracking certificates (like GOs) are transferred in combination with the

electricity. A PPA is a private document and as such the delivery of

attributes, such as the attributes delivered with a GO, would be double

counted as they are not removed from the grid-average fuel mix in a

residual mix [12]. One example of such a PPA would be that Google

contracted to buy 114 MW of wind power for 20 years from a wind project

in Ames to power Google’s Data Centre in Council Bluffs, Iowa [13].

Another Example is that Microsoft bought wind power to power part of its

22.2 MW Data Centre in Dublin, Ireland [14].

Figure 2-2 Power Purchase Agreements [13]



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3 GLOBAL INDICATORS ABOUT THE ELECTRICITY

MIX IN EUROPE

This chapter aims to introduce global indicators about the electricity mix in

Europe. On the one hand, these indicators will allow the Data Centre operators to

know the attributes of the electricity they consume from the grid. On the other

hand, these indicators could be used as decision variables in algorithms for the

management and operation of Data Centres. The chosen indicators are the share

of renewables in the gross electricity production, the primary energy factor, the

CO2 emissions factor, the energy dependency rate and the day-ahead spot

electricity price.

3.1 DESCRIPTION AND ASSESSMENT OF THE ENERGY INDICATORS

The following section aims to define the five indicators and present their

calculation. It is important to keep in mind that these indicators refer to an

electricity mix and therefore they should not be confused with energy

performance indicators for Net ZEDCs, which should be defined in the context of

a harmonized evaluation framework for Data Centres. On the other hand, they

try to be as consistent as possible with the Regulation (EC) 1099/2008 on energy

statistics developed by the Statistical Office of the European Communities,

Eurostat.

In addition, to give a baseline for these indicators across Europe, they are shown

for Spain, Germany, Sweden, The Netherlands and Italy. To do so, monthly

values for the electricity mix in these countries in 2012 from the European

Network of Transmission System Operators for Electricity (ENTSO-E) [15] have

been used.

3.1.1 ELECTRICITY GENERATED FROM RENEWABLE ENERGY SOURCES

The RES-E is the ratio between the gross electricity production from RES and the

gross national electricity consumption. It measures the contribution of electricity

produced from renewable energy sources to the national electricity consumption.

Electricity produced from RES comprises the electricity generation from hydro

plants (excluding pumping), wind, solar, geothermal and electricity from

biomass/wastes. Gross national electricity consumption comprises the total gross

national electricity generation from all fuels (including self-production), plus

electricity imports, minus exports [16].



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Figure 3-1 show how the RES-E varied along the year 2012 for the five countries.

It can be observed that the greater the share of renewable was, the more

variable the indicator became, which is understandable considering the

fluctuating nature of RES. The profiles also show that the highest shares of

renewables in electricity generation normally occur during the spring and

summer months, coinciding with improved availabilities of renewable resources

such as hydro, wind or solar energies. Nevertheless, an exception to this trend is

noticed in Spain, for which hydro and wind power had a great upturn at the end

of the year.

Figure 3-1 Profile of the RES-E in year 2012

In 2012, Sweden was the “greenest” country with 66.1% of its electricity

production coming from renewables. Sweden has large share of installed

hydropower capacity already, but 2012 was a record year in which a wet season

gave the third highest electricity production from hydropower ever recorded and

wind power broke all records, leading to the highest total electricity production

and net exports reached ever [17]. Spain was second with 32.1% of its

electricity production coming from RES, mainly wind and hydro power. Regarding

Germany and Italy this indicator was set to 22.9% and 22.2% respectively.

Although Germany spend a lot of effort to increase its renewable installed

capacity, the main part of electricity still comes from conventional fuels and

nuclear energy. On the other hand, Italy is one of the countries of the EU with

the highest dependency on natural gas for electricity generation. In a similar

manner, with a major contribution of thermal conventional fuels, the Netherlands

produced only 11.9% of its electricity from renewables (mainly from biomass and

wind).

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3.1.2 PRIMARY ENERGY FACTOR

When a Data Centre consumes electricity from the grid it has to be aware that

transporting this power has incurred several losses. These losses occur along the

whole process in which primary form of energy was extracted from nature,

transformed several times and transported to the end-consumer. In this sense,

primary energy factors (PEFs) allow estimating the primary energy which was

really consumed to satisfy the end-consumer’s demand. There are two definitions

for the primary energy factor: the total PEF and the non-renewable PEF. In the

former, all the energy overhead point of delivery is taken into account, including

the energy from renewable energy sources. Consequently, this factor always

exceeds unity. In contrast, the latter excludes the renewable energy component

of primary energy: the renewable part of delivered energy is considered as zero

contribution to the PEF. Therefore, for a renewable energy carrier, this normally

leads to a factor less than unity, ideally zero [18]. In this document, the total

PEF will be assessed and hereafter it will be referenced simply as PEF.

Theoretically, the value of the PEF depends on the nature of the primary energy

consumed, the efficiency of the generation technology and the losses of

transporting the electricity to the end-consumer. There is no unified approach in

European regulations regarding how to calculate PEFs. Each member state can

select whatever method they wish and PEFs are often used as political tools with

unclear calculation methods [19]. As far as is known, Spain is the only country

that reports PEFs of individual electricity generation technologies. Hence, the

global PEF for the five countries under study has been assessed using the factors

published by the IDAE [20] and taking the consumption point as reference. It is

important to notice that the IDAE assumes the factor for renewables to be 1,

thus the PEF will converge to 1 as the penetration of renewables increases. On

the other hand, it considers the primary energy for nuclear and solar thermal

technologies to be the thermal energy contained in the steam that enters the

turbine, i.e. the heat produced in the fission reactor and the heat produced by

solar thermal plants, respectively. Primary production of coal and lignite consists

of the quantities of fuels extracted or produced, calculated after any operation

for the removal of inert matter. Finally, the IDAE assumes that 9% of the net

electricity generation is lost in the transportation and distribution network.

With these assumptions, the global PEF (i.e. the PEF to be applied to the power

from the centralized power system) is estimated with a weighted average of the

different technologies within the electricity mix of a country. Therefore, the net

electricity produced by each technology is multiplied by its specific PEF and

summed up. Then, the sum is divided by the total net production to obtain the

global PEF.



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By applying this methodology to the five countries, the results show that

Germany was the country with the highest global PEF in 2012 with an average

value of 2.66. This was mainly due to the fact that coal and nuclear energy, with

specific PEFs of 3.04 and 3.31 respectively, had major contributions to the

electricity production of the country. In second place, although 81.6% of its

electricity production came from fossil fuels, Dutch electricity mix had a global

PEF of 2.47. The reason of that was the big share of natural gas in its electricity

portfolio, which has a relatively low specific PEF of 2.15. The same goes for Italy,

in which more than 60% of electricity was produced from natural gas, reducing

its global PEF to only 2.16. Finally Spain and Sweden, even having the higher

renewable shares, scored moderate PEFs of 2.34 and 2.12 each due to the

significant presence of nuclear energy in their electricity mixes (additionally to

coal-sourced production for Spain). The monthly seasonal profiles in Figure 3-2

show that generally the PEF tends to drop during periods in which renewables

penetration in the electricity mix becomes more important.

Figure 3-2 Grid primary energy factor in 2012

3.1.3 CO2 EMISSIONS FACTOR

Data Centre operators may also be interested in estimating the CO2 emissions

related to their power consumption from the grid. As done for PEFs, the global

CO2 emissions factor (EF) is calculated as a weighted average of the emissions

factors of individual technologies that contribute to the electricity mix. Again,

specific EFs published by the IDAE [20] were used to assess the global EF of

each country and the consumption point was taken as reference. With EFs of

1.09 tCO2/MWh and 0.8 tCO2/MWh respectively, coal and oil derivatives are the

technologies with the highest emissions rates. In contrast, natural gas has a

decreased EF of 0.44 tCO2/MWh and biomass is considered to be carbon neutral.

Of course, nuclear energy and the remaining renewables do not emit.

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As expected, the three countries with major shares of thermal conventional

technologies have higher EFs. Actually, Germany has the highest EF (0.58

tCO2/MWh) due to the high share of coal in its electricity generation. The EFs of

Netherlands and Italy, despite these countries having greater contributions of

fossil fuels, have values of 0.52 tCO2/MWh and 0.47 tCO2/MWh thanks to the

greater use of natural gas for electricity generation. Spain, with greater

penetration of renewables and nuclear energy, has a CO2 EF of 0.35 tCO2/MWh.

Finally, as it produces almost all its electricity from renewables and nuclear

energy, Sweden generates nearly zero emissions (0.02 tCO2/MWh). Again, it can

be observed in the seasonal profiles of the Figure 3-3 how the EF goes down

when renewable energy production rises.

Figure 3-3 Grid CO2 emission factor in 2012

3.1.4 ENERGY DEPENDENCY RATE

Energy dependency shows the extent to which an economy relies upon imports

in order to meet its energy needs. Eurostat defines the energy dependency rate

(EDR) as net energy imports (imports minus exports) divided by gross

consumption, expressed as a percentage [16]. This approach refers to all the

primary energy which is consumed in a country, comprising the energy destined

to cover electricity, transport and heating needs. Since this section is focused

only on the electricity mix, the definition has been applied only to the energy

carriers concerning electricity generation. Another issue to be highlighted is the

fact that the production of nuclear energy is considered indigenous in official

statistics, although all fuel, enriched uranium and reprocessed fuel for nuclear

power plants is imported from abroad. Thus, if uranium is not available in the

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country, electricity from nuclear plants has been considered as generating

external dependency.

Hence, in this document the EDR refers to the ratio between net primary energy

imports and primary energy consumption tied to electricity consumption. To

calculate this ratio, the first step is to estimate the primary energy carriers used

for electricity generation. To do so, specific PEFs have to be applied for each

technology. Then, each primary energy carrier is multiplied by an importation

factor taken from statistical information sources of each country. An assumption

is made when multiplying net electricity imports by the global PEF of the country

calculated before. Finally, the sum of primary energy imports is divided by the

primary energy consumption (calculated by multiplying electricity consumption

by global PEF of the country). Once the calculation done, the higher the EDR is

the more energetically dependent the country is. It could even happen that the

EDR exceeds 100%, which would indicate that energy products have been

stocked. In contrast, a negative EDR indicates a net exporter of energy.

Considering nuclear as imported energy, the results shown in the Figure 3-4

reveal that all the analysed countries are in some extent dependent on energy

imports. In 2012, with an average dependency rate of 81.9%, Italy was the

country which most strongly depended on imports. Actually, Italy depends on

imports of natural gas for 90.4% of its supplies [21]. In addition, it does not

have significant oil and coal deposits, thus these fuels have also to be imported.

The second most dependent country was Spain. The only significant indigenous

energy resource that Spain possesses is coal, which accounted for 56% of

electricity produced from coal in the country [22]. Without gas or oil reserves,

Spain is obliged to import them from abroad, but a greater penetration of

renewables allowed limiting EDR to 67.59%. Then, although Sweden has no

fossil resources [23], the high renewables penetration in its electricity mix

reduced significantly its dependence on abroad resources. However, as nuclear

energy is considered to be imported and it accounted for nearly 38% of the

Swedish electricity production in 2012, the dependency factor was finally

calculated to be 57.37%. The Netherlands, with 0.64% of the world natural gas

reserves, holds the second largest reserves in the EU and is the second largest

gas producer and gas exporter in Europe after Norway [24]. It is also the main

entrance gate for oil into Europe, but no significant reserves of this fossil fuel are

available in the country [25]. With these conditions, EDR of The Netherlands for

electricity production was 48.75%. Finally, Germany was the country with the

lowest dependence. Germany has considerable reserves of hard coal and lignite,

making these the country’s most important indigenous sources of energy.

However, except for the case of lignite which does not need to be imported,

about 77% of hard coal, 98% of oil and 87% of gas are imported [26] [27]. In

sum, with a significant contribution of coal to the German electricity mix, its EDR

was 46.16% in 2012.



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Figure 3-4 Energy dependency rate in 2012 (indigenous nuclear)

It is important to keep in mind that the EDRs presented above are assuming that

nuclear energy is imported. A comparison between this approach and the one

used by official statistics show that results can be very dissimilar (Table 3.1).

While all the countries are somehow energetically dependent under an

exogenous approach, this dependency is significantly lowered when considering

the nuclear energy to be indigenous. Whereas Italy (which has no nuclear power

plants) is the only country which keeps the same value, Sweden even reverses

the indicator and becomes a net exporter.

Table 3.1 Comparison between EDRs in 2012 considering nuclear as imported or

indigenous primary energy

Country ENERGY DEPENDENCY RATE

(imported nuclear) ENERGY DEPENDENCY

RATE(indigenous nuclear)

Spain 67.67% 36.63%

Germany 46.16% 24.40%

Sweden 57.37% -9.80%

The Netherlands 48.75% 44.08%

Italy 81.90% 81.90%

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3.1.5 DAY-AHEAD SPOT PRICE OF ELECTRICITY

Day-ahead spot price has been chosen to analyse the cost of electricity. This

price is the result of the auction in the day-ahead market in which suppliers and

consumers do their offers and biddings. This is the market where most power

trading transactions occur. However, the day-ahead spot price is not to be

confused with retail price paid by end-consumers for the electricity. Retail prices

include the cost of energy purchased by suppliers (that generally purchase their

energy in wholesale markets such as day-ahead markets); network charges; and

the taxes, levies and financial burdens set by national regulations [28]. As shown

in the Figure 3-5, in some countries network charges and regulated taxes can

reach a significant weight in the end-consumer final receipt.

However, as this work aims to analyse how electricity prices vary according to

factors like supply, demand and weather changes rather than regulations, day-

ahead spot price turns to be a more suitable indicator. Therefore, the data for

the analysis has been extracted from the electricity market operators – EPEX

(Germany), GME (Italy), OMIE (Spain), APX (The Netherlands) and NordPool

(Sweden). These values are depicted in Figure 3-6, which shows the evolution of

day-ahead spot prices in the five countries under study. Italy is clearly the

country where electricity prices were the highest, with an average day-ahead

spot price of 74.84€/MWh, while mean values in The Netherlands, Spain and

Germany were 48.05€/MWh, 47.26€/MWh and 42.67€/MWh. Finally, with an

average value of 32.59€/MWh, Sweden had the lower day-ahead spot prices in

2012. It must be noticed that electricity prices tend to decline in countries with

greater renewables penetration and during periods with increased production of

green power.

Figure 3-5 Example of retail price components for small industrial consumers of 5GWh in

several European regions [28]



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Figure 3-6 Day-ahead spot prices of electricity in 2012

3.2 HOURLY BASIS ASSESSMENT OF THE GLOBAL INDICATORS

RenewIT project aims to develop dynamic models which characterise the energy

consumption of Data Centres and assess its interaction with the grid. The five

indicators described in section 3.1 are expected to be variables in these models

and therefore they should also be assessed on an hourly basis. As an example,

this section presents the five indicators for Spain on an hourly basis. To do so,

data from the Spanish power system operator [29] and the market operator [30]

has been used. The graphs display the profiles of average days of four months –

January, April, July and October – representing the different seasons. Thus they

allow analysing the evolution of the global indicators during the day, while doing

a comparison of the different seasons of the year.

First, the Figure 3-7 shows that the contribution of renewables in the Spanish

electricity mix clearly increases during the daylight hours. On the other hand, the

spring is the season in which greater penetration of renewables is reached,

mainly due to the greater contribution of hydro and wind power.

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Figure 3-7 Daily profiles of the share of RES in the Spanish electricity mix

As mentioned in previous section, since the PEF for renewables is considered to

be 1, there is a correlation between the share of the renewables and the global

PEF of the electricity mix. This is evidenced in the Figure 3-8 which shows that

the higher PEF are reached during the night, when renewables are less present.

In contrast, although a mild increase is observed during the peak hours, the CO2

emission factor seems to remain quite constant along the day throughout the

entire year (Figure 3-9).

Regarding the energy dependency, Figure 3-10 shows that the higher values of

the EDR occur during the night and consistently decrease during the day. Thus

this makes it clear that the renewables help to lower the energy dependency.

Finally, the Figure 3-11 shows the evolution of day-ahead spot prices of

electricity in Spain. It can be observed that prices go hand in hand with the

demand, being the higher prices at peak periods of the day.



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Figure 3-8 Daily profiles of the global PEF of the Spanish electricity mix

Figure 3-9 Daily profiles of the global CO2 EF of the Spanish electricity mix



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Figure 3-10 Daily profiles of the EDR of the Spanish electricity mix

Figure 3-11 Daily profiles of the day-ahead spot price of electricity in Spain

3.3 DEVELOPMENT OF ELECTRICAL MIX INDICATORS IN THE FUTURE

The graphs in the Figure 3-12 show the correlation between RES-E in Spain in

2012 and the distinct indicators presented before. Although the PEF and CO2 EM

have more marked dependency, it can be observed that the EDR and the price of

electricity are also dependent in some extent to the share of renewables. Taking

this into consideration, it is foreseeable that the value of the electricity mix

indicators will evolve in the future as greater penetration of renewables, higher

efficiencies and increased transmission capacity between countries are achieved.



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Figure 3-12 Correlation between the electricity mix indicators for Spain

Actually, a study carried out by Graabak and Feilberg [31] shows that the share

of RES-E is likely to increase substantially up to 2050. According to the degree of

public involvement (reflected in the national regulations, population attitude and

business policies) and development of technologies, the report establishes four

scenarios for analysing the situation of the European electricity mix up to 2050.

The Red storyline is a kind of Business-As-Usual scenario where the energy

system develops as it did before 2010 (limited environmental awareness and few

breakthroughs in technology for energy efficiency and for renewable energy

production). The Blue storyline represents a scenario where technical

breakthroughs proliferate but in which the public is reluctant to change their

behaviour in an environmentally friendly direction. Finally, the Green and the

Yellow storylines reflect a very high public focus on environmental challenges and

the need for reduction of GHG emissions, but with distinct levels of technology

development. The Figure 3-13 shows the evolution of the RES-E between 2010

and 2050 according to these different storylines.



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Figure 3-13 Development of the share of RES-E in the different scenarios [31]

This growing share of renewables will certainly result in decreasing CO2

emissions. Table 3.2 shows the CO2 EFs for 2010 and 2050 based in a high

decarbonisation scenario. It can be observed that, besides the lower average,

2050 values show a greater seasonal variation (from summer to winter months)

than in 2010. This is due to the fact that solar energy is expected to play a

significant role in the decarbonised scenario for 2050.

Table 3.2 CO2 EFs for EU electricity grid in 2010 and 2050 in gCO2/kWhf [31]

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

CO2 EF - 2010 378 377 367 349 342 346 350 345 354 357 370 377

CO2 EF - 2050 49 51 41 18 12 13 15 13 18 23 40 46

In a similar way, the Figure 3-14 shows the expected decrease of PEFs in several

countries across Europe. The yellow bar is factor actually used in the country’s

performance standards for buildings, while blue bars indicate calculated factors

for the years 2009, 2020 and two 2050 scenarios.

In any case, this section does not aim to give accurate forecasting of the

indicators, but to raise awareness about their variability and their likeliness to

evolve rapidly in the near future, as well as the need of regular revisions of their

values in regulations.



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Figure 3-14 Development of the PEF in different countries up to 2050 [19]



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4 AVAILABILITY OF RENEWABLE ENERGY

RESOURCES IN EUROPE

4.1 RENEWABLE ENERGY RESOURCES

Generally, there are only three sources where renewable energy originates from:

Sun – energy is transferred from the sun to the earth by solar radiation.

Earth – heat from the earth’s interior reaches the surface.

Gravitation – gravitational forces between earth, moon and sun cause the

tides.

Energy from these primary sources is transferred to different energy carriers as

shown in Figure 4-1. The energy resources evaluated here are derived from

these energy carriers because they present the states of energy which can be

harvested.

Figure 4-1 Primary energy resources, usable energy carriers and evaluated renewable

energy resources

Surface water covers rivers, lakes and seas which provide different kinds of

energy. Harvesting the kinetic energy from surface water is seen as hydropower

in the following while using air, surface water and groundwater as heat sources

(or heat sinks) are classified as “environmental energy”. Another group is

“marine energy” or “ocean energy” which covers for example tidal flow and

waves (caused by wind).

Hydropower is not considered as a resource here because there is only little

potential for new plants (it will be though, analysed in the global analysis of

technologies). In 2002, already 75 % of the economically usable potential in

Europe has been used [32]. Furthermore, there are various environmental

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4.2 SURVEY OF RENEWABLE ENERGY RESOURCES IN EUROPE

The general information on the renewable resources presented in this section is

based on Ghosh [33] and Sorensen [34].

4.2.1 SOLAR ENERGY

Solar radiation can be directly used for heat or power production. Global solar

radiation consists of direct and diffuse shares which both can be harvested

depending on the technology.

The energy available from solar radiation depends on the geographical location

and varies with a daily and an annual cycle. Furthermore, it is influenced by the

weather as clouds reduce direct irradiation to the earth. Shading caused for

example by mountains or buildings also influences the availability of solar

radiation at a certain location. However, solar energy is more predictable than

wind.

Figure 4-2 shows that most solar energy is available in southern Europe,

especially on the Iberian Peninsula. However, many locations in central Europe

receive more than 1,000 kWh/m² as well.

Figure 4-2 Annual sum of global horizontal radiation in Europe [35]



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4.2.2 WIND ENERGY

Wind blows almost everywhere on earth, but not constantly – strong fluctuations

are a drawback when harvesting wind for power production. Additionally, only

wind speeds over 4 m/s are interesting for use [35]. The general potential of

wind power is high – the amount of solar energy which is converted into wind is

about 50 to 100 times the amount of solar energy converted into biomass [33].

Wind can be harvested both onshore and offshore. Offshore wind production is

interesting due to higher wind speeds and less vortices and turbulences

compared to onshore locations, but suffer from higher plant costs.

Figure 4-3 shows that the highest potential for onshore wind power is available in

Scandinavia, Ireland and Scotland. From Figure 4-4 it can be seen that a high

wind energy density is available offshore in the North Sea and along the coast of

the Baltic Sea.

Figure 4-3 Wind power potentials in Europe (km/s⋅km2) [37]



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Figure 4-4 Distribution of wind energy density in Europe for 2030 [36]

4.2.3 BIOMASS ENERGY

The term biomass covers all plant material which is either burned or used for

producing liquid fuels or biogas. Biomass is a renewable energy source as long as

the rate of extraction does not exceed the rate of production (e.g. wood). The

advantage compared to e.g. solar and wind energy is that heat or power can be

generated from biomass chemical energy without fluctuation.

Biomass can be classified in different ways. One example is given in Figure 4-5

which shows the potential of different biomass resources in European countries.

From the data shown in Figure 4-5, the biomass availability (energy density) in

each country can be calculated. The results in Figure 4-6 show that most

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Figure 4-5 Available biomass energy potential 2000 [37]

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woodfuel

forest residues

industrial residues

biomass waste



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Figure 4-6 Available biomass energy potential divided by country area [37]

4.2.4 GEOTHERMAL ENERGY

Earth’s geothermal energy originates from the formation of the planet (20 %)

and from radioactive decay of minerals (80 %) [38]. Four types of geothermal

energy resources are usually distinguished [39]:

Hydrothermal: hot water or steam at moderate depths (100–4,500

metres)

Geopressed: hot-water aquifers containing dissolved methane under high

pressure at depths of 3–6 kilometres

Petrothermal (hot dry rock): abnormally hot geologic formations with little

or no water

Magma: molten rock at temperatures of 700–1,200 °C

Geothermal energy is a steady resource without fluctuations. Figure 4-7 shows

the geothermal heat flux as an indicator of geothermal energy availability in

Europe. Locations with high heat fluxes are distributed almost over whole of

Europe.



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Figure 4-7 Geothermal heat flux in Europe [40]

4.2.5 MARINE ENERGY

Marine or ocean energy can be classified into four types [39]

Tidal energy

Wave energy

Ocean thermal energy

Salinity gradient energy

Tidal energy

Tidal energy can be harvested at locations where large tidal ranges occur. Figure

4-8 indicates that tidal power is available along the coasts of Great Britain,

Ireland and France (Northern and Western coast). These three countries have

47.7 %, 7.6 % and 42.1 % of the European tidal resources, respectively [41].



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Figure 4-8 Mean tidal amplitude at European coasts [42]

The tidal range is not constant but varies from day to day with a period of about

two weeks. The power output during neap tide is only about 30 % of the spring

tide power output [43].

Wave energy

Wave energy means using the kinetic energy of waves caused by the wind at the

ocean’s surface. Figure 4-9 shows that there is a high potential at the western

coast of Europe which is particularly high also in a world-wide scale [44].



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Figure 4-9 Wave power levels in kW/m of crest length in European waters [44]

Ocean thermal energy

Ocean thermal energy conversion (OTEC) is the utilisation of the temperature

difference between warm water at the ocean’s surface and colder water in the

deep for power generation. Generally, the main potential can be found in

equatorial regions, but there is also a very small potential in southern Europe

[44].

Salinity gradient energy

Salinity gradient or osmotic energy is the energy available from the difference in

the salt concentration between seawater and river water. As the technologies for

harnessing this energy are still under development, it is not considered here.

4.2.6 ENVIRONMENTAL ENERGY

Environmental energy means thermal energy of the air, surface water (rivers,

lakes, and seas) and groundwater which can be used for heating by means of a

heat pump. Also using these resources as heat sinks for cooling (“free cooling” or

reversible heat pump) is considered here although in this case thermal energy is

fed into the air or the water instead of extracting it. The aspect of free cooling

potential is essential in the following because Data Centre cooling is much more

relevant than heating. Regarding surface water, only sea water is taken into

consideration exemplarily.

Sea water

Sea water could be used for free cooling when it is cold enough and available at

the Data Centre’s location. Figure 4-10 and Figure 4-11 show exemplarily the

surface temperatures of European seas in January and July 2012, respectively.



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Groundwater

Groundwater is interesting for free cooling or re-cooling because annual

temperature variation is relatively low. However, the available temperature is

influenced e.g. by buildings and tunnels. Furthermore, legal conditions may limit

the application of groundwater as heat sink.

Figure 4-10 Sea surface temperatures measured in January 2012 [47]



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Figure 4-11 Sea surface temperatures measured in July 2012 [45]

4.3 SURVEY OF RENEWABLE ENERGY RESOURCES IN SAMPLE COUNTRIES

Four sample countries were chosen exemplarily for a more detailed analysis of

renewable energy availability, e.g. considering daily and annual fluctuations. The

selection of the countries was based on the following criteria:

Geographical distribution (southern, central and northern Europe)

Number of Data Centres in the country [46]

Locations of Data Centres involved in the RenewIT project

Thus, Spain, Germany, the Netherlands and Sweden were chosen. As climatic

conditions vary within these countries, reference locations are assumed for

dealing with climate data. It is important to bear in mind that these location do

not represent the climate conditions of the particular country, but are an

example for the conditions in the climate zone they are located in. Table 4.1

gives an overview on the reference locations which are also shown in Figure

4-12.



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Table 4.1 Reference locations

Country Location Latitude Climate zone

Spain Barcelona 41° 24’ N Mediterranean climate

Germany Chemnitz 50° 50’ N humid continental climate

Netherlands Amsterdam 52° 22’ N oceanic climate

Sweden Luleå 65° 35’ N subarctic climate

Figure 4-12 Sample countries and reference locations [47]

For each country, the aspired share of renewable energies in power generation

as well as heating and cooling in 2020 according to national renewable energy

action plans is presented. The particular values can be seen as an indicator for

the availability of the respective resource in the country. Table 4.2 gives an

overview on the renewable energy resources according to IRENA [48].

For each reference location, a summary with the necessary data will be shown. A

more detailed approach at the hourly behaviour of the different indicators is

made in annex 1. Concrete and detailed analysis of the resource data must be

undertaken for each concrete case and, therefore, generalisations are not

extremely valuable, especially as far as wind resource, geothermal resource and

ocean resource are concerned.



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Solar energy, despite being stochastic, is more clearly related to the latitude. We

see, hence, in the following graph the differences between direct and diffuse

radiation in the four locations. We can clearly see that, on top of having more

radiation, southern European countries present more fraction of direct radiation,

which can be helpful with solar technologies that rely on this type of radiation.

Table 4.2 Renewable energy resources in the sample countries [34]

Country Renewable energy resource

Wind Solar Biomass Geothermal Ocean

Spain

Germany

Netherlands

Sweden

high medium low unknown

Figure 4-13 Monthly direct radiation for the four locations [47]

0

20

40

60

80

100

120

140

160

Dir

ect

rad

iati

on

Month

Direct radiation (kWh/m2)

Amsterdam Chemnitz Barcelona Lulea



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Figure 4-14 Monthly diffuse radiation for the four locations [47]

4.4 ANALYSIS OF DATA CENTRE SPACE AVAILABILITY

Renewables like solar panels and wind turbines require space. This subchapter

provides an overview of the available space at data centres plots. For the

majority of the Data Centres the available ground surrounding the data centre is

limited, since Data Centre owners buy or rent what they need. When there is

space surrounding the current data centre facility, this is mainly occupied by the

Data Centre supporting areas, like parking spaces and offices, or reserved for

future expansion. Opportunities for these types of renewables arise when local

legislation does not allow for a hundred percent occupation of the plot by

buildings. This is the case, for instance, in Istanbul, where owners are only

allowed to fill their land for 50% of the plot space with buildings at some regions,

meaning that the remainder is available for instance for solar panels.

A viable place to position renewables would be the roof when this is not being

occupied by the data centre supporting systems as for instance air handling units

or chillers. The outer walls could be another good option for placing solar panels

or a green wall.

Furthermore, when a Data Centre is part of the development of a large

plot/parcel or district, the required available space or the possibilities to reuse

0

10

20

30

40

50

60

70

80

90

100

Dif

fuse

rad

iati

on

Month

Diffuse radiation (kWh/m2)

Amsterdam Chemnitz Barcelona Lulea



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heat/energy can be implemented from the start at higher level for the overall

development. This enables the complete area and all the buildings to be fit out

with the required systems, such that the plot can become a “smart grid”. Heat

reuse is especially valuable when this smart grid involves buildings or facilities

that require a constant need of heat, like swimming (tropical) pools, green

houses and some industries.

The plots of current data centres can be characterized by the following aspects:

Small data centres (<250 kW), mainly business owned, situated in

business areas and surrounded by other businesses or homes. The other

buildings surrounding cause the available space to be very limited. Due to

their small size, reusing of the waste heat is not financially beneficial.

Examples: van Lanschot Bankiers, small university data centres, hospitals.

Middle sized data centres (>250kW - <1MW) situated in business areas

and surrounded by other businesses and industries. Due to the nature of

the surrounding buildings the available space tends to be very limited. The

roof could be an option when it is not occupied by the data centre

supporting systems. If ground space would be available on the Data

Centre plot, this space is most likely reserved for expansion of the data

centre. An advantage of the proximity to other buildings and their size is

that the waste heat of the Data Centre can be transported and reused

more efficiently by the surrounding buildings.

Examples: Rabobank Boxtel, Global Switch Amsterdam, Equinix

Amsterdam, TeleCityGroup Amsterdam, Interxion Amsterdam.

Large Data Centres situated in the middle of nowhere. These are mainly

very large Data Centres (>50 MW), that are not close to any civilized

surrounding. This provides enough space for a large application of

renewables like solar panels and/ or wind turbines. An advantage is that

surrounding space is mostly relatively cheap. Furthermore, there is

sufficient space for expansion. However, for instance large scale reuse of

waste heat of the data centre is complicated by the “nature” of the

surroundings.

Examples: Google, Apple, Microsoft and Facebook.



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5 TECHNOLOGY ANALYSIS OF RENEWABLE ENERGY

TECHNOLOGIES

5.1 INTRODUCTION

The goal of this chapter is to give a brief description of the different technologies

that can be used either to directly renewable energy supply to Data Centres, to

convert these sources into usable energy or to store energy to match supply of

renewable energy sources and demand of energy.

To begin, a brief glimpse at the load distribution of the Data Centre consumption

will be given, which will be used to analyse the ways in which renewable energy

has to be transformed into energy to satisfy the Data Centres consumption. A

special focus will be put in the HVAC systems of the Data Centres, and their

morphology.

After this subchapter, the main core of the document will follow. This core is a

description of the state of the art of the different technologies that can be

combined to compound renewable energy systems for power and HVAC systems

(divided, as mentioned, between energy generation, transformation, storage,

etc.). Figure 5-1 shows the structure that will be followed in the analysis, with

the number of subchapters in each of the case.



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Figure 5-1 General scheme of the interaction of the different chapters in the technology

analysis

In this state of the art, the different technologies will be described with its basic

technical concepts and indicators, present costs and future costs and level of

maturity of the technology (research –RES-, demonstration-DEMO-, deployment-

DEP-, mature technology-MAT) [49]. For the sake of the comparison, the specific

prices will all be given in euros, using the conversion factor of 02/01/2014 (1

€=1.3659 US$).

5.2 CURRENT ENERGY CONSUMPTION OF DATA CENTRES

Table 5.1 shows the Data Centre space structure, which is divided in three

spaces: IT room, Data Centres support area and ancillary spaces. The IT room is

an environmentally controlled space that houses equipment and cabling directly

related to compute and telecommunications systems which generates a

considerable amount of heat in a small area. Moreover, the IT equipment is

highly sensitive to temperature and humidity fluctuations, so a Data Centre must

keep restricted power and cooling conditions for assuring the integrity and

functionality of its hosted equipment. Thus, many manufactures call the IT room

whitespace. The Data Centre support areas are all those areas where different

systems (power, cooling, and telecommunications) such as the uninterruptible

power supply (UPS), cooling control system and switch boards generator are

located. Finally there are the ancillary spaces which are those such as offices,

lobby and restrooms.

Table 5.1 Data Centre space structure

DATA CENTRE

IT Room Data Centre support

areas Ancillary spaces

Cabling and

Networking

Equipment

distribution

areas

Racks and

cabinets

Power system, cooling

system,

telecommunications

room

Offices, lobby,

restrooms, etc.

In this deliverable, the focus will be put on the characterisation of the HVAC

systems that are commonly used in Data Centres, which will limit the type of

renewable energy sources that might be integrated.



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5.2.1 TECHNICAL CHARACTERISTICS OF DATA CENTRES HVAC SYSTEMS

Data Centre HVAC first and foremost means cooling, i.e. removing heat from the

hardware in order to maintain tolerable temperatures of the electronic

components. At present, there exist a lot of different variants of Data Centre

HVAC solutions which differ for example in the heat carrier medium (e.g. air or

water) or in the location of the chiller (e.g. close to rack, in the server room,

central chiller for the building).

Figure 5-2 illustrates the different possibilities for moving the heat produced by

the hardware (right-hand side) to the environment (left-hand side) [50] [51]

[52]. As different combinations of certain devices are possible, these

combinations are indicated by the case numbers. For example, the water-side

economizer presented in case 2 can be applied with all room and rack

subsystems which include chilled water as heat carrier between building and

server room. Thus, the room and rack subsystems from cases 1, 5, 6, 10 and 12

can be combined with the building subsystem shown in case 2. Descriptions of

the cases are given in Table 5.2.

It is obvious that the HVAC systems contain up to five heat transfer processes

between the heat source (IT hardware) and the heat sink (environment). Each

heat transfer process is characterised by a certain temperature difference

between the heat releasing and the heat absorbing medium.

Furthermore, the figure shows at which position within the system the chiller can

be situated: close to the rack, in the server room or as a central chiller

somewhere else in the building.



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Figure 5-2 Overview on HVAC systems for Data Centre cooling



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Table 5.2 Overview on HVAC systems for Data Centre cooling

Case Description

1 Air transfers heat from hardware to computer room air handler (CRAH), e.g. with raised

floor, cold/warm aisles (primary air cooling loop); secondary water cooling loop with

chiller. This case is the standard configuration according to the literature.

2 The chiller in case 1 can be (temporarily) replaced by a waterside economizer (free

cooling). The economizer can be left out (direct water loop between CRAH and cooling

tower for free cooling).

3 Direct expansion cooling of air in the room with air-cooled condenser located outside.

4 As case 3, but with water-glycol loop for heat removal from condenser.

5 Central cooling coil; chilled-water supply from case 1, 2 or 11.

6 Heat transfer between air and water within the rack: liquid-cooled rack door which cools

the air when leaving the rack; or closed-liquid rack where air circulates within rack (rack

contains heat exchanger); chilled-water supply from case 1, 2 or 11.

7 Direct expansion cooler close to rack (e.g. in-row liquid cooler or overhead liquid cooler);

heat transport to cooling tower by water or water-glycol.

8 As case 7, but with air-cooled condenser located outside.

9 Liquid cooling within rack; heat transfer to air close to rack; chilled air supply from case 1,

3, 4, 5 or 13.

10 Liquid cooling within rack; heat transfer to secondary cooling loop; chilled water supply

from case 1, 2 or 11.

11 Air-cooled chiller instead of water-cooled chiller as shown in case 1.

12 Direct liquid cooling of hardware; chilled water supply from case 1, 2 or 11.

13 Direct free cooling with air (air-side economizer).



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5.3 RENEWABLE ENERGY TECHNOLOGIES FOR POWER SUPPLY

The first group of technologies to analyse will be the technologies for power

supply. These technologies are based on the sole production of electricity (the

process of electricity production doesn’t undergo a thermal cycle). The produced

electricity y will be used for IT loads, electrical loads (not for IT uses), and HVAC

loads. A conceptual map of the chapter is shown in Figure 5-3.

Figure 5-3 Conceptual graph of chapter 5.3



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5.3.1 GENERATION

5.3.1.1 SOLAR PHOTOVOLTAIC

The first technology we will analyse is solar photovoltaic (PV). PV is the

technology that uses the photovoltaic effect to convert solar radiation into

electricity.

The key components of a PV power system are various types of PV cells

(sometimes also called solar cells) interconnected and encapsulated to form a PV

module (the commercial product), the mounting structure for the module or

array, the inverter (essential for grid-connected systems and required for most

off-grid systems), the storage battery and charge controller (for off-grid systems

but also increasingly for grid connected ones).

PV cells represent the smallest unit in a PV power producing device. In general,

cells can be classified as either wafer-based crystalline (monocrystalline and

multicrystalline silicon, compound semi-conductor) thin film (amorphous silicon-

a-Si-, Copper Indium Gallium Selenide-CIGS-,Cadmium Telluride -CdTe, etc.) or

organic. Currently, crystalline silicon technologies account for about 80% of the

overall cell production in the IEA PVPS countries.

Taking into account latest developments [53], crystalline technologies move from

13 to 25% efficiency, compound semiconductors can reach as high as 40%

efficiency (triple junction), thin film can move from around 8-12% in a-si, to

almost 20% in the case of CIGS, and new technologies using organic materials

are still at the low range of the spectrum (4-12%).

Groups of cells are interconnected to form modules. With these modules, PV

arrays are formed. A PV array consists of a number of modules connected in

series (strings), then coupled in parallel/series to produce the required output

power. These modules have to be integrated through structures that can be

mounted directly onto roofs or integrated in the buildings (Building Integrated

PV, BIPV), including PV facades, integrated (opaque or semi-transparent) glass-

glass modules and ‘PV roof tiles’. Tracking systems have recently become more

and more attractive, particularly for PV utilization in countries with a high share

of direct irradiation. By using such systems, the energy yield can typically be

increased by 25-35% for single axis trackers and 35-45% for double axis

trackers compared with fixed systems. However, falling costs in PV cells and

maintenance criteria might not make them the best option.



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Figure 5-4 Images of two PV installations (one building integrated and another in

industrial premises) [54]

Price, in the case of PV, depends largely on the size of the plant to be installed.

[55] shows the differences in prices between the type of system installed and

the cost of the different components in the global system price, We see that the

percentage of cost of the module in the global price oscillates between a 30 and

a 40% of the global price (0.8 – 2.3 €/Wp), and the trend in the last years is a

continuous reduction of prices. In the case of Data Centres, when we are talking

either about commercial rooftop or utility mounted on the ground (either fixed

tilt or one axis tilt), prices in 2011 oscillate between 2.3 and 3.4 €/Wp.

As far as future prices are involved, the short-term evolution seems to show that

prices will be significantly reduced, in next years. In fact, [56] indicates that

around 2050, costs of systems of significantly under 1.32 €/Wp, which in

countries with good solar radiation data (over 1,400 kWh/kWp), can mean a LEC

of 9.52 c€/kWh, significantly lower than the current costs of conventional

electricity sources



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5.3.1.2 WIND ENERGY

The second renewable energy resource historically harvested is wind. Wind

energy is the conversion of the kinetic energy of wind into a useful form of

energy, like mechanical energy (pumping) or electricity (through the use of wind

turbines integrated with electric generators). Wind turbines are the main element

harvesting this kinetic energy. They can be divided into small wind power (less

than 50 kW, according to IEC 61400 2 Ed2) and big wind power systems.

These latter systems can be either onshore (placed on solid land) or offshore

(placed in the middle of the sea), with the only difference being the size

(offshore locations, because of a smoother surface of the surrounding area can

support bigger turbines and therefore more power harvesting) and the structural

requirements.

Wind energy is widely used, either in stand-alone mode or in grid-connected

systems. Until recently stand-alone systems tended to use small wind turbines

and grid-connected systems used bigger wind turbines. But the apparition of new

electrical storage technologies (for isolated applications, like islands), and small

urban wind turbines has created new combinations and now we can find big wind

turbines in stand-alone applications (San Cristobal island, Galapagos, Ecuador)

or small wind turbines on the roofs of buildings inside big cities.

Wind energy depends basically on the capacity of the turbine for harvesting the

wind power, being the maximum amount of power the amount of kinetic energy

of the wind, which depends on the area covered by the turbine blades (A), the

density of the air ( and the velocity of the wind (v). The harvested energy is,

therefore,

.

However, not all the kinetic energy of the wind can be harvested. The maximum

physical efficiency of the system, according to Betz’s law is 59% of the total

kinetic energy of the wind. This has obviously to be reduced by the mechanical

efficiency of the turbine and the electrical efficiency of the generator.

Moreover, because of the variability of the wind, a wind farm's total electricity

production is not the addition of the generator ratings multiplied by the hours of

the year. The ratio of real electricity production by the formerly mentioned

multiplication is called the capacity factor. Typical capacity factors are between

15% and 50% in big wind farms, and lower than 15% in small wind power

systems.



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Figure 5-5 Offshore park near Copenhagen [57]

Prices in wind energy oscillate depending on the type of windfarm (onshore,

offshore). [58] quotes installed prices of onshore farms of around 1,100€/kW,

with average capacity factors depending on the country, but tending to 40%.

[56] quotes slightly higher prices for onshore farms (1,391 €/kW), but with

similar capacity factors. Moreover, [58] states that the trends in the wind market

seems to go to improve capacity factors in locations with smaller wind resource.

On the other hand, offshore farms have higher prices [59], of around 2,415

€/kW but have higher capacity factors (tending to 50%).

Near future prices [59] in onshore farms seem to show no further cost reduction,

but in offshore farms they seem to be able to be under 2,196 €/kW.



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5.3.1.3 HYDRO ENERGY

Although new hydro resource is not available in Europe, and therefore, this type

of energy is of little use for existing and future data centres, we have included a

short subchapter in the basic concepts of hydroelectric energy plants.

Hydroelectric power plants use the gravitational force of falling water in rivers to

move a turbine which, as it turns, moves an electrical generator that produces

electricity.

These plants can either use high heads with relatively low flows or high flows

with relatively low heads to generate electricity. In the second case, the civil

works requirements of these plants can be significantly increased, making it in

most cases necessary to build dams to even the water flow. The different types

of water resource (relationship between flow and head) will set the conditions for

the type of water turbine to be chosen.

Figure 5-6 Two typical designs of a high-flow low head hydro power facility (left) and a

low-flow high-head power facility (right) [57]

The wide range of sizes and capacities of the different hydro plants has led to the

classification of all hydroelectric facilities between pico, micro, small and large. In

some cases (for instance in California), large hydro plants have been considered

as non-renewable resource, because of the enormous impact on the land and

environment they have [60], whilst others [61] claim that large hydro can even

have less impact than small hydro.

The capacity factors in the case of hydro power plants depend basically on the

characteristics of the river they have been designed for. If a variable design was

prioritised, low capacity factors might exist (i.e. the Three Gorges Dam doesn’t

have more than a 50% capacity factor). Moreover, in some cases, hydroelectric



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plant's production may also be affected by requirements to keep the water level

from getting too high or low and to provide water for fish downstream.

The basic efficiency in hydroelectric power systems depends on the mechanical

efficiency of the turbines (which in current designs is a value usually greater than

90%) and the electrical efficiency of generators, which is higher than 95%.

[59] states that the costs of hydro power have reached its minimum level, with

values of around 3,000 €/kW.

5.3.1.4 OCEAN MECHANICAL ENERGY TECHNOLOGIES

New and promising technologies are lately appearing in the harvesting of ocean

resources. Oceans have the potential to deliver a huge amount of energy, either

using their thermal capacity or their mechanical energy. In this chapter we’ll

focus on the generation of electricity thanks to the mechanical energy of oceans.

Mechanical energy of oceans can be either tidal energy or wave energy. Normally

wave energy, driven by the winds, is generated by the movement of a device

either floating on the surface of the ocean or moored to the ocean floor. Many

different techniques for converting wave energy to electric power have been

studied.

Wave conversion devices that float on the surface have joints hinged together

that bend with the waves. This kinetic energy pumps fluid through turbines and

creates electric power. Stationary wave energy conversion devices use pressure

fluctuations produced in long tubes from the waves swelling up and down. This

bobbing motion drives a turbine when critical pressure is reached. Other

stationary platforms capture water from waves on their platforms.

This water is allowed to runoff through narrow pipes that flow through a typical

hydraulic turbine.

Figure 5-7 Pelamis wave turbine and SeaGen tidal energy harvesting [62]

Wave energy is proving to be the most commercially advanced of the ocean

energy technologies with a number of companies competing for the lead.

http://en.wikipedia.org/wiki/Fish



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On the other hand, tidal energy is the movement of the oceans due to the

gravitational force of the moon. The potential energy that can be harvested is

the difference in water height from low tide and high tide. Tidal energy is, hence,

usually captured using barrages across estuaries, and using hydro turbines to

harvest the potential energy.

In both cases, systems are still in their development phase, with some

demonstration projects, and not yet in their deployment phase. Therefore, costs

are still high but with an interesting falling trend.

Out of [59], current costs, in the case of ocean wave power plants can reach

6,765 €/kWel, whilst tidal power plants can have lower costs, closer to 4,304

€/kWel. In 2030, [59] mentions that costs of both plants can approach 2,343

€/kWel, reaching competitiveness closer to market prices.




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5.3.1.5 SUMMARY OF POWER-ONLY GENERATION THROUGH RENEWABLE ENERGY RESOURCES

A summary of the most interesting technical characteristics of electrical generation with renewable energies is shown in Table

5.3.

Table 5.3 Summary of power only generation through renewable energy resources

Technology Solar

photovoltaics

Wind

power onshore

Wind power offshore

Hydro Power Ocean-wave

energy Ocean-tidal energy

Power range 100 W-100 MW

1 kW-5 MW 3-5 MW 500 kW-500 MW 5 kWel-6 MWel 250 kWel-2MWel

Electric conversion efficiency 6-40% 25-33% 25-33% 85-95% 25%-43% 5-15%

Capacity factor

13%-20%

(depends on climatic

conditions)

20-40% 40-50% 15%-99%

Current installation costs

2,200-3,000 €/kWp

1,500-1800 €/kW

3,300 €/kW 1,200-5,000 €/kWel 7,000 €/kWel 4,000 €/kWel

Future installation costs <1,800 €/ kWp

1,500-1,800

€/kW 2,950 €/kW 1,200-3,500 €/kWel 3,200 €/kWel 3,200 €/kWel

State of the art DEP DEP DEP MAT DEV DEV




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5.3.2 ELECTRIC ACCUMULATION1

The former means of electric power generation are highly erratic, and therefore

its penetration in power systems can lead to problems related system operation

and the planning of power systems. These problems may be especially important

in islanded grids. Therefore, renewable energy power generation facilities are

required, in accordance with grid codes, to present special control capabilities

with output power and voltage, to withstand disturbances and short circuits in

the network during defined periods of time. In this way, wind farms are known

as wind power plants. In this scenario, Energy Storage Systems (ESS) play an

important role in renewable energy power applications by controlling plant output

and providing ancillary services to the power system and thus, enabling an

increased penetration of renewable energy power in the system.

Electrical energy can be converted to many different forms for storage:

As Pumped Hydro Storage (PHS). PHS is a large scale energy storage

system. Its operating principle is based on managing the gravitational

potential energy of water, by pumping it from a lower reservoir to an upper

reservoir during periods of low power demand. When the power demand is

high, water flows from the upper reservoir to the lower reservoir, activating

the turbines to generate electricity. The energy stored is proportional to the

water volume in the upper reservoir and the height of the waterfall. The use

of PHS can be divided into 24 h time-scale applications, and applications

involving a more prolonged energy storage in time, including several days.

Actually, there is a tremendous potential for hydro-storage capacity in many

areas globally. In daily storage applications, the potential is around 1675

GW, and for more prolonged storage, 1454 GW. This technology is the most

used for high-power applications.

As Compressed Air Energy Storage Systems (CAES). CAES are based on

conventional gas turbine technology. In this type of system, the energy is

stored in form of compressed air in an underground storage cavern. When

energy is required to be injected into the grid, the compressed air is drawn

from the storage cavern, heated and then expanded in a set of high and low

pressure turbines which convert most of the energy of the compressed air

into rotational kinetic energy. The air is additionally mixed with natural gas

and combusted. While the turbines are connected to electrical generators in

order to obtain electrical energy, the turbine exhaust is used to heat the

cavern air.

1 This chapter of the state of the art is entirely summarized directly from the co-author

Francisco Díaz’s article [81]



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As electrochemical energy in batteries and flow batteries (BESS). Batteries

are one of the most used energy storage technologies available on the

market. The energy is stored in the form of electrochemical energy, in a set

of multiple cells, connected in series or in parallel or both, in order to obtain

the desired voltage and capacity. Each cell consists of two conductor

electrodes and an electrolyte, placed together in a special, sealed container

and connected to an external source or load. The electrolyte enables the

exchange of ions between the two electrodes while the electrons flow

through the external circuit. BESS is a solution based on low-voltage power

battery modules, connected in series / parallel in order to achieve the desired

electrical characteristics. BESS comprises batteries, the Control and Power

Conditioning System (C-PCS) and the rest of the plant, which is in charge of

providing good protection for the entire system. Many types of batteries are

now mature technologies. In fact, research activities involving Lead-Acid

batteries have been conducted for over 140 years. Notwithstanding, a

tremendous effort is being carried out to turn technologies like nickel–

cadmium and lithium-ion batteries into cost effective options for higher

power applications.

As chemical energy in fuel cells (HESS). Hydrogen can be obtained in various

ways: by means of water electrolysis, from renewable energies such as solar

or wind installations, gasifying biomass, coal or fuel (which is the most

common option). When hydrogen is produced from renewable energy power

plants, it can be stored in order to be used directly in fuel cells, or

transported to users through pipelines to produce electricity. When hydrogen

is stored, the technology used is known as Regenerative Fuel Cell (RFC). It is

composed of the following components: a water electrolyzer system, a fuel

cell system, a hydrogen storage and a power conversion system. This

technology is responsible for carrying out the electrochemical

transformations in order to store energy in the form of hydrogen and inject it

as electricity into the grid, when required. As presented, electrolyzers are key

parts of RFCs. By means of these devices, water is electrolytically

decomposed into hydrogen and oxygen. There are many types of

electrolyzers, from common technologies such as Alkaline electrolyzers, to

more modern types like Polymer Electrolyte Membrane (PEM) electrolyzers.

As they are flow batteries, RFC power and energy capacity are not related

characteristics. In addition, since they are designed in a modular manner,

high energy systems with more than 100 MW h and with high peak power,

more than 10 MW, can be achieved. Their practically zero self-discharge

(depending on the type of hydrogen storage) allows these systems to store

energy for long periods of time. In terms of their useful life and cycle life,

they are estimated at more than 15 years and 20,000 charge and discharge

cycles (at 100% of DoD) respectively. Finally, notice that one of the major

drawbacks of a RFC is its low energy efficiency, about 42%, due to the



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relatively low energy efficiencies of the fuel cell and the electrolyzer, about

60% and 70% respectively.

As kinetic energy in flywheels. A Flywheel Energy Storage System (FESS) is

an electromechanical system that stores energy in form of kinetic energy. A

mass rotates on two magnetic bearings in order to decrease friction at high

speed, coupled with an electric machine. The entire structure is placed in a

vacuum to reduce wind shear.

As magnetic field in inductors. The Superconducting Management Energy

Storage (SMES) system is a relatively recent technology. The first system

based on this technology was built in 1970. Its operation is based on storing

energy in a magnetic field, which is created by a DC current through a large

superconducting coil at a cryogenic temperature. The energy stored is

calculated as the product of the self-inductance of the coil and the square of

the current flowing through it. Thus, the characterization of the coil has a

central role in the system design. Depending on the system operating

temperatures, superconducting coils can be classified as: High Temperature

Coils (HTS), which work at temperatures around 70 K, and Low Temperature

Coils (LTS), a more mature technology, with working temperatures around 5

K. A balance between cost and system requirements determines the

technology used.

As electric field in capacitors. Supercapacitors (SCESS) are also known as

ultracapacitors or double-layer capacitors. Like batteries, supercapacitors are

based on electrochemical cells which contain two conductor electrodes, an

electrolyte and a porous membrane whereby ion transit between the two

electrodes is permitted. However, no redox reactions occur in the cells,

because the operating voltage is lower, in order to electrostatically store

charge on the interface between the surfaces of the electrolyte and the two

conductor electrodes. In fact, this structure creates two capacitors (due to

both interfaces, electrolyte – negative electrode and electrolyte – positive

electrode), and for this reason, they are called double-layer capacitors.

As far as efficiency for the different systems, Figure 5-8 shows the values:




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Figure 5-8 Energy efficiencies of all different electric accumulation technologies

A brief summary of the main characteristics of all electric accumulation system is

done in Table 5.4.

Table 5.4 Summary table for electrical accumulation [63]

Technology PHS HESS CAES VRB ZBB PSB

Power rating

(MW) 10-1,000 0.1-50 50-300 0.2-10 0.1-1 0.1-15

Specific energy (Wh/kg)

- 100-

1,000 3.2-5.5 20-35 60-85 30-65

Capital cost (€/kWh)

10-70 2-15 3-70 450 375 125-1,000

State of the art MAT DEMO DEV DEV DEV DEV

Technology NaS Lead-acid

Ni Cd Li Ion SMES FESS SCESS

Power rating (MW)

0.05-34 0.05-10 45 0.015-50 1-100 0.1-20 0.05-

0.25

Specific energy (Wh/kg)

100-175 35-50 30-80 10-200 10-200 5-100 1-30

Capital cost (€/kWh)

210-250 150-270 350-

2100

700-

1000 300-650 6,800

State of the art DEV MAT MAT MAT DEMO MAT RES



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5.3.3 CONVERSION

In the conversion chapter, when dealing with purely electrical technologies, we

have to distinguish between IT consumption, electrical consumption from the

rest of equipment in the Data Centre and HVAC consumption.

IT consumption and electrical consumption require no more transformation from

renewable energy power systems than the ones included in the renewable power

generation systems (inverters in the case of PV or small wind power systems,

etc.). On the other hand, to convert electricity into cooling we need special

devices (compression chillers/heat pumps) that can turn the electricity into cold.

As mentioned in the introduction, we will consider aerothermal heat pumps as

state of the art, and we’ll focus, as renewable energy sources, on geothermal

heat pumps.

5.3.3.1 GROUND SOURCE OR NATURAL WATER SOURCE HEAT PUMPS

Because of its thermal stability with regards to seasonal changes, the ground in

the first 100-200 meters is an adequate medium either for energy storage or as

energy source. In the case of ground source heat pumps and cooling demand

(which is the case in Data Centres), it can be used as the energy sink. For the

same criteria, water source in rivers, lakes, seas and oceans can be used to

dissipate the energy.

Ground source heat pumps have the same principle as conventional heat pumps

(air-air and air-water), and they can therefore heat, cool and, if adequately

equipped, supply domestic hot water with greater efficiency.

Ground source heat pumps can be open or closed loop cycles. In the case of

closed loop cycles, they consist of buried heat exchangers (either horizontal or

vertical) with a thermal fluid that transfers the heat from the internal space to

the ground. However, because of the continuous requirement of heat dissipation

in the case of Data Centres (and the lack of heat extraction), closed loop systems

seem to have little applicability to Data Centres.

Figure 5-9 The three different types of ground source heat pumps [64]

On the other hand, open loop cycles consist on systems where the heat transfer

fluid (underground water) flows freely underground and acts not only as a heat



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sink, but also as a medium for the heat transfer. The main technical challenge of

these kind of systems is the drilling and to be able to take advantage of the

phreatic layer. In most cases, two wells are necessary, one to extract

underground water and the other to inject it.

Present costs for open loop cycles can be found between 1000 and 2000 €/kW,

(including wells), being open source loops the first case [64] and closed loops

with vertical boreholes the second (own data from different projects from

Aiguasol).

As far as future costs are concerned, prices seem to be stable, and although

some reduction in costs could be attained, the reduction in price seems not too

significant.




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5.4 RENEWABLE ENERGY TECHNOLOGIES FOR LOW-ENTHALPY HEAT

GENERATION

5.4.1 INTRODUCTION

Low-enthalpy heat generation cannot be converted into electricity for Data

Centre consumption. Nevertheless, this resource can be important for the use of

reducing the HVAC loads, producing cold through this low-enthalpy heat

generation. This chapter will therefore be dealing with the technologies of low-

enthalpy heat generation, the technologies to use this heat to produce cold (heat

extraction) and finally the technologies of accumulation that can help match

demand and supply (given the stochastic condition of some renewable energy

resources).

The conceptual map of the different subjects addressed in the chapter is shown

in Figure 5-10.

Figure 5-10 Conceptual map of the chapter

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5.4.2 GENERATION

5.4.2.1 SOLAR THERMAL COLLECTORS

The first generation systems we deal are solar thermal collectors. Solar

thermal collectors harvest solar radiation to convert it into heat. Since the

objective of this heat, in the case of thermally driven cooling technologies,

is to produce cold (extract heat), and the thermally driven cooling processes

require some high temperatures, we’ll focus on collectors that can handle

them.

The input temperature range required of the solar part of solar cold

production systems depends on the type of cooling equipment used, which

will be defined in next chapters: 50 °C or more, for desiccant cooling based

open systems, 65 ºC or more for adsorption chiller based closed systems

and 85 ºC or more for absorption chiller based closed systems. Due to this

temperature difference, the choice of the most suitable solar collector type

varies according to cooling equipment type.

Different collector technologies have been developed in order to achieve a

higher efficiency at higher temperatures. Two major types of solar collectors

can be considered for providing the temperatures required in closed solar

assisted air conditioning systems:

Stationary collectors. These collectors do not use any mechanisms to

track the sun. They can produce heat at low and medium

temperatures (up to 150 °C). Flat-plate collectors, evacuated tube

collectors and compound parabolic concentrator (CPC) type

concentrators, belong to this group of collectors.

Concentrating tracking devices (Parabolic trough collectors, linear

Fresnel collectors, tower systems). These are sun tracking collectors

used both in solar process heat plants and in large power plants for

solar thermal electricity generation. Temperatures up to 400 °C can

be obtained with good efficiency.

In addition to these collector types that offer better efficiency at high

temperatures, solar air collectors offer good results at low temperatures and

are therefore suitable for applications such as desiccant cooling.

The efficiency of solar collectors is () of a solar collector is defined by the

ratio of the power delivered to the load (circulating fluid) to the incident

solar irradiation on the aperture area of the collector. The efficiency is

usually represented as a function of TGT / where T (K) is the difference

between the average fluid temperature (the temperature of the fluid used to

extract the collected power) and the atmospheric temperature; and GT

(W/m2) is the amount of incident solar radiation available to the collector.


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Figure 5-11 Solar thermal flat plate collectors and linear Fresnel collectors [65] [66]

The instantaneous efficiency is thus written as TGTTccc /*)( 210 ,

where c0 is the optical efficiency (a function of collector cover transmission,

receiver absorption and reflectivity of mirrors in the case of concentrators)

and c1, c2 are the linear and quadratic heat loss coefficients; parameters

that characterise the heat losses from the collector to the atmosphere

(including convection, conduction and radiation heat loss mechanisms). c1

(W/K m2); c2 (W/K2m2).

In Figure 5-12 from [67], the efficiency of different type of collectors is

shown as a function of temperature difference between ambient air and

average temperature inside the collector. It is important to see that,

depending on the use of solar thermal heat, the most adequate type of

collector is one or another. For instance, in the case of using heat for

cooling with absorption machines, the level of temperature of activation is

around 90ºC. Therefore, collectors like ETC or concentrating collectors seem

the most adequate. It is important to point out, though, that the

concentrating collectors depend only on the direct radiation available, which

is the only means of radiation that can be concentrated. It means therefore,

that in places with a high percentage of diffuse radiation (sky and ground),

the available energy is much lower for concentrating collectors.


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Figure 5-12 Efficiency curves for different collectors and different thermally driven

chillers, for ambient temperatures of 25ºC and radiation 800 W/m2 [67]

As far as the present costs on solar thermal energy collectors are

concerned, based on previous studies, we can see that there is an important

scattering of values, although they move from around 700 €/m2 in small

sizes to around 300-400 €/m2 in bigger sizes [68].

If we cross it with the efficiencies of the collectors it means, as an example

[69], for a location like Barcelona, that levelised energy cost of solar

thermal energy, at 90ºC (which is a correct working temperature for

thermally driven cooling machines), the cost of energy is between 15 and

35 c€/kWh, still important with regards to conventional fuels.

As far as future costs are concerned, the evolution of prices of solar thermal

has had two main drivers: the size of the collectors, which has allowed a

reduction in installation costs, and the development and cost reduction of

concentrating collectors, which despite having moving parts they have a

very interesting potential cost reduction, because of the materials they are

compound of. We see that costs should, according to Figure 5-13 be in 2030

under 300 €/kW in the lower range.


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Figure 5-13 Trends in costs in solar thermal [70]


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5.4.2.2 RE BOILERS (BIOMASS, BIOGAS, SYNGAS, BIODIESEL)

Another type of renewable energy generation consists in using off-site

resources (biomass, biogas, syngas, biodiesel) to produce heat directly

through a combustion process, in renewable energy boilers.

Renewable energy boilers are based on the principle of transforming the

energy capacity of renewable energy biomass sources (solid biomass,

biogas, biofuels) into heat through direct combustion.

The main market solution for these types of boilers is focused on solid

biomass, which is the renewable energy which costs less and has an easier

means of being transported and bought.

Biomass boilers can be classified by various methods based either on the

physical characteristics of the boilers or in the fuel type they use.

As far as the physical characteristics of the boilers are concerned, two main

aspects have to be addressed: operating temperatures and internal

technical characteristics of the boilers.

Renewable energy boilers can be used to heat water under its boiling point,

to make superheated water (over 100ºC), to make steam or to heat other

thermal fluids. The operating temperature of the boiler is important, since it

can be connected either to different types of thermally driven cooling

machine, with significant differences in cooling transformation efficiency.

Figure 5-14 Industrial boiler, to be used with hot water, superheated water, steam

[71]

As far as the internal technical characteristics of the boilers, they can be

either water tube boilers, using water as working fluid inside the pipes, or

fire tube boilers, using flue gas inside the pipes. They can also try to take


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advantage of condensation, in low temperature levels, although this is

unusual for solid biomass.

The efficiency of the mentioned boilers range from 80% in the case of

superheated water or steam boilers to 104% in the case of condensing

boilers.

As far as the fuel type is concerned, they can use either pellets, woodchips,

logs or other agricultural residues. A first approach on the lower heating

value, humidity and density of each of the fuels is shown in Table 5.5.

Table 5.5 Basic data of biofuels

BASIC DATA BIOFUELS

Pellets Woodchips Agricultural residues

LHV (kcal/kg) 4,066 3,206 3,744

Humidity (dry base) 8% 25% 10-40%

Density (kg/m3) 650 200 200-500

Content in ashes 0.5% 1% 1-2%

As far as prices are concerned, prices for different technologies for hot

water are between 500 and 1200 €/kW (quotes from manufacturers to

AIGUASOL in projects ranging from 50 kW to 2 MW).

5.4.2.3 GEOTHERMAL LOW-ENTHALPY SOURCES

They are treated together with high-enthalpy sources in 5.5.1.2.

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5.4.3 CONVERSION INTO COOLING

There are two groups of thermal processes for the conversion of heat into cold, the known as thermo mechanical processes

(which, at the moment, are still at research state) and heat transformation processes, which start to be widely used. In this

subchapter, we’ll focus on the latter.

counterflow absorber

liquid sorbent

desiccant rotor fixed bed process

solid sorbent

open cycles

ammonia-water water-lithium bromide

liquid sorbent

absorption

adsorption

(eg. water-silicagel)

dry absorption

(eg. ammonia-salt)

solid sorbent

closed cycles

heat transformation process

rankine cycle

vapour compression cycle

steam jet cycle Vuilleumier cycle

thermomechanical process

thermal process

solar thermal collector

biomass boiler

chp

general r.e. source

Figure 5-15 General graph of conversion of thermal energy into cooling




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In these processes, we first have to generate the heat to move the process

(which will result in heat extraction from a source). The generation heat can

come from renewable energy sources.

Nevertheless, the thermal processes producing cold relatively high temperatures

of the heat source (>60ºC), which has made it necessary for certain renewable

energy heat sources (i.e. solar thermal) to adapt its technology to this concrete

levels of temperature.

Two main groups of systems exist, inside the heat transformation group:

Closed cycle cooling (or thermally driven chillers), both absorption and

adsorption types, operate on the basis of a process that permits heat transfer

from a low temperature source to a high temperature source. This is made

possible by using additional heat from a higher temperature level.

Table 5.6 Summary table for closed cycle cooling [72]

Process Absorption Adsorption

stages single effect double effect triple effect single effect

ab/adsorbent lithium bromide / water silica gel

refrigerant water / ammonia water

generator T. 80 ºC – 110 ºC 140 ºC - 160

ºC 190-250ºC 60 ºC – 95 ºC

flow hot water or

overheated water overheated

water or steam hot water

COP 0.6 - 0.8 0.9 – 1.2 1.3-1.6 0.4 – 0.7

market capacity

< 35 kW incipient market < 50 kW (Sort.)

35 kW to 100 kW few manufacturers

>100 kW wide market

50 – 350 kW (May.)

>100 kW wide market 70 – 1220 kW (Nis.)

manufacturers

Climatewell, Rotartica, Sonnenklima,

Schucö, Yazaki, Broad, EAW, Carrier, Trane, York, LG Machinery, Sanyo-

McQuay, Entropie, Thermax, …

not yet in

commercial status. Kawasaki

has a first prototype

Sortech, Mayekawa, Nishiodo

pictures

Open Cycle cooling (DEC): Open cycle cooling processes are those, in which

the air that is to be cooled (or dehumified) is in direct contact the working

medium of the cooling process itself. The refrigerant. as it is in direct contact

with the air - is always water. These processes consist of a combination of

sorptive air dehumidification and evaporative cooling (desiccant and



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evaporative cooling. DEC). The COP strongly depends on the environmental

conditions (e.g. ambient air temperature and humidity). In Central European

climates values between 0.5 and 0.7 have been obtained [72].

Table 5.7 Summary table for open cycle cooling [72]

Type of thermally driven machine

Solid dessicant DEC Liquid dessicant DEC

ab/adsorbent Water-silica gel Water-CaCl

Water-LiCl Water-LiCl

Sorbent phase solid liquid

Generator temperature 50 – 95 ºC 50 – 70 ºC

COP 0,5 – 0.7 >1

Available technology in market

Dessicant machines Menerga

Typical cooling power 20 kW – 350 kW

(each module)

pictures

Nevertheless, it is important to state that even though in thermal processes we

do basically use thermal energy to drive the cooling source of the machine, there

is always a requirement of electric energy for parasitic consumptions (fans,

pumps, valves) that any thermal process needs.

Present costs in the case of the different machines depend strongly on the size of

the project. According to [73],the cost of absorption machines in Europe begins

(at power <100 kW) at costs of around 600-1,000 €/kW and reaches an

asymptote at 300 kW, with a cost of around 300 €/kW.

Adsorption machines, according to [73], depend also strongly on size, and

oscillate between 800-1,200 €/kW in lower power machines and reaches a

minimum cost around 500 kW with a cost of around 400 €/Kw.

Desiccant cooling depends on the cubic meters of air moved, more than the kW.

Their cost moves, therefore, from 8-12 €/m3/h, in airflows of less than 20,000

m3/h to a minimum of 5 €/m3/h in higher volumes of airflow. It can mean

(depending on external temperatures and relative humidities) specific costs

between 50 and 300 €/kW, although its use in certain conditions (very dry places

or very humid places) is not extremely recommendable.



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5.4.4 STORAGE

In the case of heat and cold, the same as in the case of electricity, accumulation

allows as well stabilising the stochastic energy generation by renewable energy

sources. Heat and cold storage, because of the local characteristics of heat and

cold generation, are even more necessary than electric accumulation.

We will focus in two types of storage: heat storage (daily and seasonal) and cold

storage.

5.4.4.1 HEAT STORAGE

Short time heat storage

Heat accumulation has a long story of usage, mainly in the form of sensible heat.

Accumulators using water (in low temperature levels) or thermal oils (in higher

temperature levels) are state of the art technology. However, the new evolution

techniques in storage, and the ones that permit a higher penetration of

renewable energy heat technologies fall in the field of seasonal thermal energy

storage and new storage techniques (phase change materials and the

technologies commonly known as thermochemical storage).

New technologies in conventional short time heat accumulation are basically

oriented at

Large solar thermal accumulators integrated in the building

Cylindrical polymeric tanks

Vacuum insulation tanks

Heat accumulation costs [73] in small sizes move from 2,000 €/m3 to 3,500

€/m3.

Seasonal storage

Seasonal storage basically consists of big heat accumulators, normally

underground, to take advantage of the ground temperature stability. The

technology of large scale seasonal thermal energy storage is investigated in

Europe since the middle of the 70´s. First demonstration plants were realised in

Sweden in 1978/79 [74] based on results of a national research programme.

Seasonal heat storage offers a great potential for substituting fossil fuels using

waste heat from cogeneration heat and power plants (CHP) or solar energy for

domestic hot water preparation and space heating. Large scale seasonal stores in

(solar assisted) district heating systems have in comparison to decentralised

heating systems lower specific investment costs and reduced relative thermal

losses.



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Four main types of seasonal thermal energy stores are in operation in German

research and demonstration plants. The four storage concepts shown in Fig. 2-2

include tank and pit thermal energy store with and without liners, borehole

thermal energy stores (BTES) and aquifer thermal energy stores (ATES).

Standard (stainless) steel or fibre reinforced plastic tanks may be mentioned as

alternative type.

Figure 5-16 Four types of seasonal thermal energy stores [74]

Basically, these four types have the following characteristics:

Water tank: storage in water, with between and 60 and 80 kWh/m3 of heat

capacity, stable ground conditions, and 5-15 m deep.

Gravel-water pit : storage in water-gravel, with between and 30 and 50

kWh/m3 of heat capacity, stable ground conditions, and 5-15 m deep

Borehole Thermal Energy Storage : storage in soil/rock, with between and

15 and 30 kWh/m3 of heat capacity, stable ground conditions, and 30-100

m deep

Aquifer Thermal Energy Storage: storage in natural aquifer layer (sand-

water), with between and 30 and 40 kWh/m3 of heat capacity, stable

ground conditions, and 20-50 m thickness of aquifer.

Costs of all seasonal thermal storage are shown in the following graph

(logarithmic scale), reaching as low as 50 €/m3 in very large accumulation tanks.



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Figure 5-17 Specific storage costs of demonstration plants (cost figures without VAT)

[74]

Other accumulation systems

Phase change materials

Organic and inorganic phase change materials (PCMs) offer a wide range of

possible melting points and by this storage temperatures. Most of the Materials

that are suitable for cold storage are inorganic salt hydrates. They offer high

latent heat and low cost. Known problems of salt hydrates are incongruent

melting, supercooling and poor nucleation. For notes about avoiding these

problems see [74].

Possible organic PCM materials are paraffin and fatty acids. Organic compounds

show a latent heat capacity that is about half of that of inorganic materials but

they have several advantages like melting without segregation into components

and no supercooling effects. Furthermore they are non-toxic, non-corrosive and

chemically inert. A disadvantage of organic PCMs is the low thermal conductivity.

The main problem for the technical implementation of the PCM technology is an

insufficient transport of thermal energy between the storage material and a

working fluid which is the necessary interface between the storage and a specific

application.



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Reasons are low thermal conductivities of the materials as well as contact

resistances and a small energy transferring area [74].

Analogous to 4.3.1 organic and inorganic PCMs can be encapsulated in micro- or

macro capsules. Microcapsules are more advantageous in terms of energy

transport and capacity rates for charging and discharging. Encapsulated PCM can

be filled in regular steel- or concrete-tanks and a suitable working fluid, e.g.

water for temperatures above 0 °C, can be used for charging and discharging.

Also compound materials consisting of PCMs and thermal conductivity enhancing

additives (e.g. graphite) are developed to overcome the problem of energy

transfer into the storage material [74].

Sorption storage

Commonly known as thermochemical reactions, the storage systems based on

the capacity of association and dissociation of water. Sorption storage involve a

reversible chemical reaction, absorption, adsorption or a hydration process [74].

In an endothermic chemical reaction a reactor is continuously fed with reactants

as it absorbs thermal energy. For discharging of the storage the reaction

products are returned to their initial state in an exothermic process.

Adsorption systems, working in open or closed cycles, can be used to produce

cold, utilizing waste heat from any thermal process or solar energy. In an open

sorption system, water is used as the adsorbate. Air transports water vapour and

heat in and out of the packed bed of solid adsorbents. In the desorption mode a

hot air stream enters the packed bed, desorbs the water from the adsorbent and

leaves the bed cooler and saturated. In the adsorption mode, the previously

humidified, cool air enters the desorbed packed bed. The adsorbent adsorbs the

water vapour and releases the heat of adsorption. The air exits warm and dry.

The energy storage density of sorption storage is generally high but the

technology is at an early stage of development. Economically and technically

feasible systems have not been demonstrated yet.

5.4.4.2 COLD STORAGE

Market available storage concepts for cold storage are chilled water storages,

phase change materials (PCM) including snow and ice storages and underground

thermal energy storage (UTES). The usage of thermochemical reactions for cold

storage is another promising technology but not market ready yet.

Cold storages can be used for short and long-term storage. They are most widely

used for daily storage cycles and are more economic by reducing the necessary

peak demand of chillers and moving the cold energy production into off-peak

seasons than saving energy.

Sources for cold can be conventional chillers or heat pumps but also natural

sources like ambient air, surface water from the sea, lakes or rivers, snow or ice.

For long term storage also a combined heat and cold storage can be an



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interesting option especially in combination with UTES. In this case e.g. the

waste heat from comfort cooling of a building during summer is charged into the

ground and can be used for heating of the building in combination with a heat

pump in winter, see [74].

Especially if the temperature level of stored cold coming from natural sources

can be used directly (without chillers) high seasonal performance factors in the

range of 6-40 can be reached for a cooling system and thus high energy savings

and a favourable economy are possible.

Chilled water storage

Chilled water storages are the most cost effective and simplest possibility for cold

storage. Common storage temperatures normally range between 4 °C and 18 °C.

Because of the low temperature difference compared to heat storage larger

storage volumes are necessary to store the same amount of thermal energy.

Crucial for an efficient storage process is good temperature stratification in the

storage volume, which is more difficult to reach for cold storages than for heat

storages because of the lower temperature difference and by this also lower

density difference inside the storage volume. In this respect also the fact that

water reaches its highest density at 4 °C has to be taken into account.

Stratification devices can be used to enhance stratification as well as multiple

storage concepts. However, thermal losses increase when multiple tanks are

used and hydraulics and controls become more complex and error-prone.

Phase change materials for cooling

Cold storage systems using PCM use the latent heat of the phase change from

solid to liquid of the storage material to store thermal energy. Suitable materials

that can be used are ice, snow and other organic or inorganic materials.

Available materials and technologies are described in the following.

The most extended use of Phase Change materials is ice. The latent heat of

fusion of ice to water at 0 °C is 333 kJ/kg. This amount of heat is equivalent to

the energy demand necessary to heat one kg of water by 80 K. To use this type

of store the refrigeration equipment has to be operated at working temperatures

below normal operation conditions for air-conditioning. Ice can be produced e.g.

at low cost periods and cold can be used at peak times.

Different concepts are described.

Ice on coil: In the ice on coil concept, also referred to as static type, a

refrigerant or a brine solution is circulated in an array of coils which is

installed in a water tank. Ice is formed around the coils in the water

volume until a certain layer-thickness is reached.



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Ice slurries: Ice slurries are super-cooled water or thin glycol solutions

that are composed of water or glycol and ice pieces. This ice water is

usually produced in ice harvesters by running a thin water film over a

cooling plate. On the surface of the cooling plate an ice layer builds. Once

the ice layer reaches a certain thickness it is removed mechanically from

the outside. The ice water then can be stored in a separate tank.

Encapsulated ice: Another possibility to overcome the problem of an

increasing thermal resistance of a growing ice layer is to pack the storage

medium in small casings that are surrounded and cooled / heated by a

non-PCM working fluid. This technology is not restricted to water as a

storage medium but is also used with other PCM materials.

Snow storage: The storage of natural snow or ice is a very old technique

that was used world-wide before cooling equipment was developed. In the

last 25 years seasonal snow and ice storage technologies have been

developed in Canada, USA, Japan and Sweden [74].

Present prices in the case of ice storage can be found between 150 and 300

€/kWh of energy accumulated (data coming from real life examples from

Aiguasol, quotes from distributor SEDICAL). Future developments might help

reduce these costs, although little data were found with regards to this.



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5.5 RENEWABLE ENERGY TECHNOLOGIES FOR HIGH ENTHALPY HEAT

GENERATION

In the previous chapter we mentioned the conversion of low enthalpy heat into

cold. If the energy source has a higher temperature level attained by the heat

medium, we can manage to produce electricity out of the heat and still recover

an important part of heat to produce cooling.

Combined heat, cooling and power (CHCP) or trigeneration is defined as the

simultaneous production of useful heat, cold and electric power in the same

plant. The biggest advantage of trigeneration is the high total efficiency this

gives resource effective operation which is crucial if the emission targets are to

be fulfilled but also for achieving economic viability.

5.5.1 GENERATION

5.5.1.1 SOLAR THERMAL POWER

Although solar thermal has been more widespread used for generation of heat

for heating and cooling purposes, the generation of electricity is another

application for the solar technology. Nevertheless, electricity generation with

thermal sources requires medium to high temperature thermal generation, in

order to be able to have acceptable efficiencies.

Dish

A solar dish system uses a large, reflective, parabolic dish, focusing the radiation

that strikes on the dish and focusing in one single point. Solar dish systems are

normally used together with Stirling engines, although sometimes steam

engines, Brayton cycles.

Dish systems (which are normally tied to Stirling engines) have a two-axis

moving systems, moving always perpendicularly to the sun. The concentrator

has limit angles of around 45º and a focal short relationship (5 to 12 m). The

temperatures are around 700ºC to 800ºC, with energy flows of between 500 and

3,000 KW/m2 [75]

There are different options of support configuration, either using a continuous

Surface or groups of discrete surfaces. For example, the different reflectors can

be either mirror-metal, aluminium film, polymer silver, tensioned membrane.

http://en.wikipedia.org/wiki/Parabola



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Figure 5-18 Example of solar dish with a stirling engine [75]

The usual areas of Stirling dishes are between 40 and 150 m2 (electrical power

between 10 and 25 kW). Nevertheless, some experiences of more than 400 m2

exist (Australian dish).

As far as costs are concerned, it is foreseen that they reduce their values from

the 8000-10,000 €/kWp to quite lower prices (4,000 €/kWp) when they are mass

producted.

Ptc and Fresnel collectors

Parabolic through collectors and linear Fresnel collectors have been described in

chapter 5.4.2.1. In the case of power production, the temperature limit is around

500ºC. The power flows is between 20-80 kW/m2.

They can be coupled to Rankine cycles, either to Organic Rankine cycles when

dealing with medium temperature linear concentrating collectors (T<250ºC)or to

conventional steam Rankine cycles in the case of dealing with high temperature

concentrating collectors (T>250ºC) [59].



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Figure 5-19 Image of Parabolic Through Concentrator [75]

The capacity factor of the plants is between 20-50%, and they keep increasing

their capacity factor, decreasing the costs of maintenance (a 30% decrease in

cost according to [59]). Nevertheless the apparition of accumulation systems can

increase the capacity factor of the different plants.

Their current costs range from 2,200 to 3,500 €/kWel, though the minimum

economically feasible (not demo) power plants linked to steam turbines can be

found around 50 MWel. Future cost reductions seem to be focused on the

development of Fresnel linear collectors, being able (Novatec product,

http://www.novatecsolar.com/ ) to reach 1,800 €/kWel. [76]

Smaller sizes are clearly oriented to Organic Rankine Cycles, with currently high

costs (5000 €/kWel).

Tower centrals

Although solar tower centrals seem to be out of scale for relatively small

applications (less than 50 MWel), new developments have brought lately to

potentially interest applications in the lower range of power. The AORA tulip DST

concept can produce up to 100 kWel per unit and 170 kWthermal.

Figure 5-20 Image of a small tower system. [77]

http://www.novatecsolar.com/



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The main idea in solar tower centrals is the development of centrals

concentrating solar energy in two axis, focusing all the radiation that goes to a

field of heliostats to a central tower, which reaches extremely high temperatures

(250ºC-1100ºC), which can be harvested through Rankine cycles, Brayton cycles

or combined. Power flows of between 300 and 1,000 kW/m2 can be harvested.

Annual efficiencies with regards to final electricity production (including any of

the aforementioned technologies) are around a 12% and a 16%. Considering the

land occupation, the efficiency is of a 5% of the total land occupied.

Costs of solar thermal power centrals are now higher, although in close future

they can reach values of around 3,100 €/kWel. [59]

5.5.1.2 MEDIUM AND HIGH ENTHALPY GEOTHERMAL SYSTEMS

The geothermal resource can be defined as the fraction of geothermal energy

that can be harvested in a technically and economically way. The concept of

geothermal energy is so wide that can go from the heat we can find in the upper

layers of ground to the depths we can reach with from the oil sector perforation

techniques [78].

Basically, the resources that seem interesting for electricity and heat generation

are:

High enthalpy geothermal resources: they can be mainly found in places

with high geothermal gradients (usually between 1500 and 3000 m). They

are compound of systems with dry steam and mixtures of steam and

water. At the temperature level they can reach, the steam (dry or

saturated) can be used with steam turbines to produce electricity.

Medium enthalpy geothermal resources: they can be found in places with

high geothermal gradients, usually in depths of less than 2,000 m. Their

temperature allows electricity production (using Organic Rankine Cycles)

and heating and cooling production for different appliances.

Figure 5-21 Example of geothermal harvesting Rankine cycle. Sizes between 2 and 45

MWel [78]



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Costs for combined heat and power with geothermal energy, either with high-

enthalpy or with medium temperature geothermal resources can be found

between 4,400 and 11,000 €/kWel.

5.5.1.3 BIOMASS THERMAL POWER

Direct combustion

In previous chapter direct combustion of biomass and its conversion into low-

enthalpy thermal energy in boilers has been widely described. When dealing with

high-enthalpy power generation, biomass can be used in steam generating

boilers, which can make the steam reach temperatures and pressures high

enough to move steam turbines or Stirling engines.

Gasification

Gasification is a thermochemical process of incomplete combustion which a gas

mixture called synthesis gas or syngas is obtained. The gasification process

consists of four stages: drying, pyrolysis, combustion and reduction. They are all

carried out in the gasification reactor or gasifier. Gasifiers are mainly classified

based on the form of contact between the solid phase and the gas or in other

words by type of bed phase. [79]

Fixed bed gasifiers have fixed biomass solid particles through which bed

gasification agent (air) moves. Depending on the direction of the air flow

on the direction of movement of bed reactors can have counter-current

flow or upward (updraft), parallel or downstream (downdraft) and cross-

flow (Crossdraft) .

Fluidized bed gasifiers utilize the same gasification processes and offer

higher performance than fixed bed systems, but with greater complexity

and cost. Similar to fluidized bed boilers, the primary gasification process

takes place in a bed of hot inert materials suspended by an upward motion

of oxygen-deprived gas

Since gasifiers are still at an early stage, real costs of gasifiers by suppliers Logic

energy [80], Kuntschaar [81], have supply costs of between 600 €/kWsyngas to

1300 €/kWsyngas.

Price evolution of gasifiers has a long potential of reduction in next years.




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5.5.1.4 SUMMARY OF HIGH-ENTHALPY THERMAL GENERATION TECHNOLOGIES

Table 5.8 Summary for high-enthalpy thermal generation technologies

Technology Solar dish Linear

concentrator

Solar Tower

central

Geothermal

sources

Biomass direct

combustion standalone

Biomass

gasification

Power range 10 kWel-400

kWel

25 kWel-300

kWel

100 kWel-

1200 MWel

5 kWel-6

MWel

250 kWel-

2MWel

250 kWel-300

MWel

Electrical efficiency (with

usual associated CHP systems)

23% 12-16% 12-16% 35-45% 40% 23-30%

Thermal efficiency

Capacity factor 15-50% 15-50% 15-50% 95% 95% 95%

Required surface

(including shadows) 10-15 m2/kWel 15-20 m2/kWel

15-20

m2/kWel

Current installation costs 8,000-10,000

€/kWel

2,200-3,500

€/kWel

3,500-4,000

€/kWel

4,400-

11,000 €/kWel

3,800-4,000

€/kWel

3,000-5,000

€/kWel

Future installation costs 4,000 €/kWel

3,500 €/kWel

State of the art DEMO DEP DEP DEP DEP DEV




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5.5.2 CONVERSION TO ELECTRICITY

5.5.2.1 GAS TURBINES

Gas turbines are rotary thermal machine operating under the Brayton power

cycle. A rotary compressor absorbs atmospheric air and its pressure rises. The

compressed air enters the combustion chamber where it mixes with fuel, usually

natural gas. This mixture is ignited producing hot combustion gases at high

pressure. These gases passing through the turbine to transfer energy to its axis

of rotation, at the same time drives the electric generator. The electrical

efficiency of these plants is in the range 30-40%.

Its performance is significantly penalized at partial loads.

At the exit there are two possible configurations:

Direct output: The gases escaping from the turbine directly environment

maintaining a temperature level of 500° C, useful for industrial processes,

generating steam , hot water for commercial or domestic use and heat

input for thermally driven cooling machines.

Heat recovery: The gases exiting the turbine passes through a heat

exchanger to preheat the incoming air in the combustion chamber. This

intermediate phase increases the electrical efficiency of the turbine, but

decreases the thermal level of the exhaust gases. However, this

temperature level is still significant (around 250-30° C) and able to be

exploited in many applications (in the case of Data Centres, especially

cooling).

Using either configuration depends on the need in each particular case

temperature. Costs of gas turbines, in big sizes are around 900 €/kWel [56].

5.5.2.2 MICROTURBINES

Until recently cogeneration systems with gas turbines lower than 1MWel had no

economic viability. Nevertheless, in recent years the situation is changing

rapidly. Equipment manufacturers are increasingly developing smaller systems

and there are even home use micro turbines. In general we can find micro

turbines with an electrical output of up to 300kWel.

Micro turbines are small high-speed central generators which consist of a turbine,

a compressor, an alternator (all on the same axis), an exhaust heat recovery (to

ensure acceptable mechanical performance) and power electronics for supply

electricity to the grid. Micro-turbines have only one moving part and require

significantly less lubrication than alternative engines. The use of renewable

energies together with micro turbines is basically focused in either biogas or

syngas, although important adaptations and gas filtering should be done.



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Micro turbines are smaller in size than alternative engines for the same installed

power, maintenance costs are lower and can reach up to 80,000 hours of

operation. They have a good performance on environmental issues, giving low

NOx = 10-25 ppm (O2 - 15 % equivalent) low operational noise level 70 dB (A)

at 1 meter. In efficiency can reach an overall yield of 78 % with electrical

efficiency of up to 33%. Currently micro turbines are supplied complete modules

so that the installation is easy in direct connection to the mains. It is also

possible to connect several modules in parallel. Costs of micro turbine are

between 1500 and 1800 €/kWel [82].

5.5.2.3 EXTERNALLY FIRED GAS TURBINES GAS TURBINES

The externally fired gas turbine (EFGT) is not a new concept, as several EFGT

plants where build between the years 1930- 1960. At this time they were used to

fire fuels like coal, mine gas and blast furnace gas.

Nevertheless, accessibility and reduction in costs of “clean” fossil fuels like

natural gas and oil, which could be burnt in internally fired gas turbines lead to a

diminish of interest in EFGT technology. At present, a new grown interest in the

EFGT technology has flourished, much thanks to increasing oil and gas prices but

also due to increasing focus on environmental friendly energy. The idea is to

utilize an EFGT with renewable biomass. The technology is currently under

development by several institutes and companies. Some of the most prominent

include the University of Rostock, the Swedish Royal Institute of Technology,

Talbotts Biomass Energy and Compower AB and Turbec. Costs of EFGT are

between 2000-2500 €/kWel [82].

5.5.2.4 STEAM RANKINE TURBINES

Steam turbines are rotating machines working under Rankine cycle. The working

fluid is water and it changes state (liquid - gas as a cycle). There are two ways to

operate a Rankine cycle turbine, under condensation or backpressure. In both

cases, the outgoing steam of the turbine still has enough energy to be used in

thermally driven heat pumps.

The range of fuels used to generate heat in the steam generator in the case of

renewables is all the previously mentioned technologies which can generate heat

out of renewable energy sources (solar thermal, geothermal, biomass). The

electrical efficiency of these power cycles can exceed 40 %. Moreover, their

response to partial loads is better than a gas turbine.

Costs of steam turbines can be found between 1200-5000 €/kWel, depending on

the size.

5.5.2.5 STIRLING ENGINES (FOR SOLAR THERMAL AND BIOMASS)

The CHP technology based on Stirling engines is an interesting application for

small biomass systems and for solar dish systems. [75]



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Stirling engines are based on a closed cycle, where the working gas is alternately

compressed in a cold cylinder volume and expanded in a hot cylinder volume.

The advantage of the Stirling engine over internal combustion engines is that the

heat is not supplied to the cycle by combustion of the fuel inside the cylinder, but

transferred from the outside via a heat exchanger in the same way as in a steam

boiler.

Stirling engines especially designed for CHP plants using solid biomass fuels and

for small scale solar dish systems have been developed at small commercial

scale. Usually, hydrogen or helium is used as the working gases at a maximum

mean pressure of 20-4.5 MPa. The utilisation of low molecular weight gases, like

Helium, makes it difficult to design piston rod seals, which keep the working gas

inside the cylinder and prevent the lubrication oil from entering the cylinder.

The type of gas used has influence in the global efficiency, which oscillates

between 30% (helium) and 40% (hydrogen).

Figure 5-22 Stirling engine and Stirling cycle

The efficiency of the Stirling cycle for high temperatures is significantly high, and

in the case of harvesting the excess energy of the regenerator and producing

cooling, it can be an interesting technology.



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Figure 5-23 Efficiency of a Solar stirling system [75]

5.5.2.6 ORGANIC RANKINE CYCLE TURBINES

The power generation system based on the Organic Rankine Cycle is an

advanced, fully enclosed binary cycle, based on a simple evaporation process.

The binary cycle power plants operating on this cycle have a wide field of

application resources temperatures above 120 ° C. These cycles can also be used

with lower temperatures (geothermal, biomass or solar thermal), but with higher

costs and lower efficiencies when converting heat to electricity.

ORC power plants uses as working fluid, an organic nature (typically a

hydrocarbon such as propane, butane or isopentane). Rankine cycle includes four

processes that change the state of the secondary fluid, which involves, as main

device , an evaporator , a turbine , a cooling tower and a feed pump ( see Figure

5.4 )

Figure 5-24 ORC from Turboden, installed in Burgos [83]

The conversion efficiency of gross energy of ORC power plant is based on the

initial temperature of the heat source, increasing from 5.5% at 80° C to 12% at

a temperature of 180 ° C.



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It means that organic Rankine cycles can be used for all the thermal power

sources mentioned (biomass, solar thermal, geothermal, combination of all of

them).

The main drawback of the Organic Rankine cycle is its limited ability to adapt to

possible changes in the variables that influence the process. Control parameters

such as temperature, sometimes just ends meet when drilling and testing phase

is completed, preventing the previous design of geothermal plants.

Although ORCs are a proven and reliable technology, prices are quite high, with

regards to other technologies (around 3,000-3,300 €/kWel).

5.5.2.7 INTERNAL COMBUSTION ENGINES (ICE)

Reciprocating engines are used in cogeneration internal combustion engines

operating under the same principles as their counterparts in automotive gasoline

or diesel. They have a higher electrical efficiency between 35 and 50%

(depending on the fuel and powers thereof).

The thermal energy is obtained from the exhaust gas and the internal cooling

circuit of the engine (cooling circuit shirts, intercooler, and oil lubrication). This

implies that thermal energy is obtained at two levels (exhaust gas around 400 °

C, cooling circuits and lubrication, around 85 ° C). This is approximately half of

the thermal power at each level.

This limits their availability according to which thermal uses. In addition to low

power motors (low flow of exhaust gases) are chosen more often leverage these

to increase the water temperature drop previously heated with cooling circuits.

Thus, the maximum thermal unit level obtained is 90 ° C.

The behaviour of this type of machine is good at partial loads, since their

electrical performance remains almost constant up to 50 % load. Below this

percentage it falls rapidly.

There are two types of motors according to the thermodynamic cycle describing:

Diesel cycle and Otto cycle.

Compression Ignited cycles (Diesel cycle) diesel They are used in CHP

plant scale, predominantly four stroke engines with direct injection with

turbocharging and intercoolers, their cooling systems are more complex

than in the case of starters led and hot water is typically obtained at 85° C

. Efficiencies in the shaft are usually around 35 to 50% and the power

range goes up to 15MWe.

Spark Ignited cycles (Otto cycle) spark ignited engines have a

performance somewhat lower, between 25% and 43%, and its maximum

power is about 6 MWel. This engine is suitable for cogeneration in small

facilities , often with heat recovery systems and exhaust gas cooling



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Prices oscillate between 800 and 2,500 €/kWel, in the case of ICE with heat

recovery.

5.5.2.8 FUEL CELLS

In the part of electrical accumulation 5.3.2 fuel cells have been described in

detail.

5.5.2.9 COMBINED CYCLE

A final technological alternative of conversion of heat into electricity is the

combination of several of the previously mentioned technologies:

Gas turbines + steam turbines

Fuel cell + ORC

ICE+ORC

ICE+ Steam turbine

Fuel cell + gas turbine

With these combinations, electrical efficiencies of over 60% can be attained.




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Technology Gas

turbine Microturbine

EFGT gas turbine

Steam turbines

Internal

Combustion Engines

ORC Fuel Cells Stirling

Power range 1MWel-450

MWel

25 kWel-300

kWel

100-300

kWel

100 kWel-

1,200 MWel 5 kWel-6 MWel

250 kWel-

2MWel

250 kWel-

300 MWel 1 kWel-250 kWel

Electrical efficiency 30-40% 25-33% 25-33% 20-40% 25%-43% 5-15% 30-65% 12%-20%

Thermal efficiency 30-45% 30-45% 30-45% 30-50% 50-60% 50-60% 20-40% 50-60%

Capacity factor 95-98% 90-98% 90-98% 98% 92%-97% 98% >90%

Required surface 0.037-0.065

m2/kWel 0,12 m2/kWel

0,12

m2/kWel 0.01 m2/kWel

0.02-0.03

m2/kWel

0,06

m2/kWel 0,15 m2/kWel

Current installation costs

900 €/kWel 1,500-1,800

€/kWel 200-2,500

€/kWel 1,200-5,000

€/kWel 1,100-2,500

€/kWel 3,300 €/kWel

Future installation

costs 900 €/kWel

1,200-3,500

€/kWel

1,100-2,000

€/kWel

3,300

€/kWel

Maintenance costs 0,005

€/kWhel 0,008 €/kWhel

0,008 €/kWhel

0,0027 €/kWhel

0,009 €/kWhel 0,002

€/kWhel

State of the art MAT DEMO RES MAT MAT DEMO DEV MAT

Usable renewable energy technologies

Solar tower, solar dish,

biogas, syngas

Biomass,

geothermal

Linear

collectors, Solar tower, solar dish, biomass,

biogas,

syngas

Biogas,

biodiesel, syngas

Linear

collectors, Solar tower, solar dish, biomass,

biogas,

syngas

Biogas,

syngas

Solar dish,

geothermal, biomass

Table 5.9 Summary of electricity conversion technologies




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5.5.3 STORAGE

High enthalpy thermal systems require either thermal accumulation or electrical

accumulation, to stabilise the plant production. In the field of thermal storage

(electrical storage was dealt with in chapter 5.3.2, new developments have been

done in accumulation of high temperature energy are focused on oil, molten salts

or concrete. The main objective is to reach values under 20 €/kWh, although

with very low efficiencies (10-30%) [75].



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6 POTENTIAL OF ON-SITE RENEWABLE ENERGY

SYSTEMS

6.1 INTRODUCTION

This chapter analyses the potential of some on-site renewable energy schemes to

fulfil the energy needs of Data Centres. To do so, it gives a first approach at the

potential schemes that can be made out of the previously described technological

blocks. Therefore, a first analysis of the maximum production in the four

different locations mentioned in chapter 4 will be proposed, based on the most

conventional schemes that have been used up to the moment either in Data

Centres or in conventional buildings with important cooling and power

requirements.

These numbers will give us a hint on the real possibilities of on-site power

generation in different Data Centres, taking into account currently existing power

consumption.

As far as the potential schemes that can be used in Data Centres out of the

previously mentioned technologies, they can be used in different ways.

Generally, there are three strategies which are shown in Figure 6-1 and which

can be combined:

A. Use of renewable heat (e.g. solar heat or heat from biomass)

B. Use of renewable power (e.g. photovoltaic or wind power)

C. Use of renewable cold (chiller driven with renewable energy or free

cooling, e.g. with ambient air or sea water)

Additionally, heat from cooling might be recovered for further application

(strategy D).



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Figure 6-1 General strategies for use of renewable energies in Data Centres



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6.2 ANALYSED SCHEMES

Though the four previous strategies can bring thousands of schemes, the

schemes we will focus on, based on previous experiences will be based on

different “pieces” of the technology puzzle, as shown in Figure 6-2.

Figure 6-2 Different pieces of the puzzle, that have to be combined to be able to

compound the systems

Schemes for power supply with renewables

Solar PV+ conventional chiller

Wind energy + conventional chiller

Solar PV+ ground source heat pump

Wind energy + ground source heat pump

Schemes for low-enthalpy z supply with renewables (only HVAC)

Solar thermal+ absorption chiller single effect

Biomass + absorption chiller double effect

Schemes for high-enthalpy thermal supply with renewables (power and HVAC)

Biomass gasification CHP + absorption single effect

Fresnel collector + ORC + absorption single effect



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6.3 CONSUMPTION OF AN DATA CENTRE REFERENCE CASE

Although in future deliverables, current energy consumption scheme of Data

Centres will be analysed, to understand the order of magnitude of consumptions

in Data Centres, some first approximate numbers for typical Data Centres that

will be used in the technology analysis chapter to evaluate the necessary space

requirements that each on-site technology would require.

For this, the data from [84] was used. Quoting the same paper, “the idea was to

define IT load capacity of around 1 MW on a Mediterranean location to easily

scale the tools developed to other DC on this region. The selected DC was placed

in Barcelona with an IT load of 1125 kW and a total built area of 1375 m2. The

objective was to calculate the energy consumption of DC, distributed between

electricity load and cooling load”. The consumption considered in [84] from a

typical DC was, hence:

Table 6.1 Consumption in a typical Data Centre

Yearly energy consumption (MWh)

Specific energy consumption(kWh/m2)

IT load 9,855 7,167

Electricity 1,421 1,033

Miscellaneous 591 430

HVAC systems cooling 11,191 8,138

HVAC systems electrical consumption (combined COP=2)

5,595 4,069

TOTAL 17,462 12,700

Figure 6-3 Division between consumption requirements

57%

8% 3%

32%

Consumption requirements 1350 m2 Data Centre

IT load

Electricity

Miscellaneous



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6.4 RESULTS OF ON-SITE ENERGY PRODUCTION FOR EXAMPLE DATA

CENTRE

6.4.1 METHODOLOGY AND INDICATORS

The first rough numbers from this first deliverable have to be used as an

indication on the orders of magnitude in case we wanted to cover all the energy

loads with some of the most conventional renewable energy onsite schemes (the

ones previously mentioned).

We have calculated specific energy production of the different schemes based on

simulations with TRANSOL 3.0 (solar cooling and solar ORC production systems),

Energy pro (CHCP schemes), PV-GIS (photovoltaic schemes) and own developed

wind harvesting tools, based on datasheets of small wind turbines (wind

schemes).

This numbers are not focused on cost but on the requirements of space of each

of the technologies. Three main outputs will be given, in each of the cases for

each technology and each of the four locations:

Required power

Necessary surface

Renewable energy fraction using available space in prototype building

For solar technologies, angle of inclination has been optimised according to

annual production data. Moreover, shadows between rows of solar based

technologies are based on avoiding shading between rows in central hours (solar

12:00) in flat roofs in December (i.e. Sweden will only have a row of solar based

technology in the roof). Occupation of small wind turbines on roofs are based on

a single frontline of wind generators in one of the sides of the building.

In the case of low-enthalpy thermal technologies, which can only deliver HVAC

loads, we will use also their combination with photovoltaic to give a better idea of

the necessary surface.

6.4.2 RESULTS

The first schemes that will be analysed require the total coverage of the energy

consumption (electrical + HVAC) using renewable energy sources. In the case of

HVAC, we have considered that the reference systems have a combined COP

(where fans are also accounted for) of 2.

In the case of ground source heat pumps, the combined COP is considered to be

different for each case, depending on the ground temperature. It will therefore

be 3 for Spain, 3.5 for Germany, 3.5 for the Netherlands and 4 for Sweden.



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Table 6.2 General rough numbers on required power and space for several configurations

Spain Germany Netherlands Sweden

PV + conventional chiller

Required installed power 12,536 20,617 20,118 22,679 Necessary surface 224,404 649,717 719,559 13,645,136

R.E. fraction using available space in prototype building

0.88% 0.30% 0.27% 0.01%

Wind + conventional chiller

Required installed power 40,098 13,941 5,513 9,926 Necessary surface 1,002,439 348,525 137,836 248,160


0.12% 0.36% 0.91% 0.50%

PV + ground source heat pump

Required installed power 11,359 18,014 17,090 19,815 Necessary surface 88,740 140,732 133,513 154,805


1.11% 0.39% 0.36% 0.02%

Wind + ground source chiller

Required installed power 36,332 12,181 4,683 8,673 Necessary surface 908,308 304,519 117,087 216,826


0.16% 0.47% 1.19% 0.65%

Solar thermal + abs 1E (+FV)

Required installed heating 66,706 104,555 145,608 151,304 Required power 8,519 14,011 13,672 15,412

Necessary surface 370,849 1,044,034 1,441,300 25,919,430 R.E. fraction using available space in prototype

building 0.79% 0.28% 0.23% 0.01%

Biomass + abs 2E (+FV)

Required installed heating 1,798 1,798 1,798 1,798 Required power (PV) 8,519 14,011 13,672 15,412

Required monthly biomass recharge 272 272 272 272 Necessary surface (biomass accum+tech room) 109 109 109 109 R.E. fraction using available space in prototype

building 32.64% 32.25% 32.23% 32.05%

Gasification + CHP + abs 1E

Required heating 2,331 2,331 2,331 2,331 Required power 1,483 1,483 1,483 1,483

CHP power 4,769 4,769 4,769 4,769 Required monthly biomass recharge 1,519 1,519 1,519 1,519

Necessary surface (biomass accum+gasifier+machine)

709 709 709 709

Necessary surface 37,085 37,085 37,085 37,085 R.E. fraction using available space in prototype

building 100.00% 100.00% 100.00% 100.00%

Fresnel + ORC + abs 1E

Required heating ORC 2,331 2,331 2,331 2,331 Required power ORC 1,483 1,483 1,483 1,483

ORC power 10,596 10,596 10,596 10,596 Necessary surface 400,872 1,266,374 1,843,540 27,602,960


0.34% 0.11% 0.07% 0.00%



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6.5 FIRST RECOMMENDATIONS AND PARTIAL CONCLUSIONS

Out of Table 6.2, one of the important conclusions that can be extracted is that

on-site energy production (wind or solar) has enormous difficulties in being able

to cover for a significant solar fraction. On-site generation with off-site energy

(biomass) might offer more options of supplying a nearly zero Data Centre,

because of the reduced space it requires versus other less energy dense

technologies.

Referring to this low potential, we detect that it is hence important to undertake

important energy efficiency measures in the Data Centres and reduce their

consumption. Otherwise, the deployment of Nearly Zero Data Centres will hardly

be possible.

Another important point to make is that though some technologies seem

interesting from the HVAC point of view, the technologies that can deal

simultaneously with electricity and cooling are the most promising to be able to

reach high renewable energy fractions in Data Centres.

As chapter 4 has pinpointed, solar resources in the southern European countries

are more significant, and it causes that these technologies make more sense in

these locations. As far as wind energy is concerned, the choice of a concrete

location in Southern Europe (Barcelona) with very low wind availability is not

representative of the wind resources available in these countries, since in other

locations wind speeds are as significant as they are in Northern European

countries. Moreover, the special conditions of urban spaces tend to significantly

reduce the potential wind production.

Two of the mentioned aspects (space availability and urban difficulties) brings us

to the interest of Data Centres nearby airports and other open spaces, which

might offer interesting options for renewable energy production on-site.



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7 EXAMPLES OF EXISTING DATA CENTRES WITH

RENEWABLE ENERGY

7.1 INTRODUCTION

Only a minority of European data centres derive energy from renewable sources.

The motivation for those that do is usually to gain positive publicity or curry

favour with regulators rather than purely for commercial reasons. The amount of

power generated by the renewable sources is often less than 5% of the total

capacity consumed by the Data Centre.

The main challenges in using renewable energy for Data Centre power are

reliability, the costs, the capacity aspects, integration of renewables and the

unpredictability of its implementation and availability. The economic feasibility is

thus related to the fact that Data Centres have very high energy densities and in

general for renewables this is not the case.

In general, the existing data centre infrastructure is characterized by a

continuous power flow but renewable energy sources, such as solar and wind,

are characterized by a fluctuating power production based on the day, time and

season. This implies that a power utility connection, based on the maximum

capacity of the data centre, is still required, hence not reducing the power utility

network connection costs. Main roadblocks for using renewable energy to power

data centres are the perceived costs, the possible negative impact on the

reliability and the lack of tools to help operators make optimal decisions and

predictions about renewable energy. A trend however is present that more and

more Data Centre owners are buying “green power” from the power utility

company.

When applying a renewable to a data centre the main objectives are reliability (it

should not have a negative influence on the reliability of the data centre) and the

financial aspect. For instance, when applying direct air cooling, a back-up system

should be present to take over when no direct air can be used. This back-up

system accomplishes a certain and required reliability.

On the other hand, to minimize the risk of a windmill located on the data centre

plot, it should not stand too close to the data centre building, such that when for

example a blade breaks off, this will not intrude the data centre and cause down

time.

Concerning the financial part, systems for data centres should have a relatively

short earn back-time (ROI), implying that the investment for a renewable energy



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should be limited. Next to these two important aspects, of course, also the local

laws and rules are influencing the decisions of data centre owners.

Therefore, the last years, mainly the efficiency improvement of the mechanical

and electrical infrastructure has been emphasized. The cooling of data centres

has become more efficient, with technologies like direct air cooling or indirect air-

to-air cooling. The decreasing PUE number also illustrates this mechanical and

electrical system efficiency improvement. Many focus on the PUE of a data

centre, which does not take into account the use of renewables nor the uses of

other resources as water consumption. However, when applying energy efficient

cooling this has a positive effect on the PUE of a data centre.

When taking into account every aspect of reducing the energy use of the data

centre and the application of renewables, many examples can be provided. Below

some examples of data centres where some kind of renewable is applied.



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Table 7.1 Overview of Examples of Applied Renewables in Data Centres

ATES

Sea water

cooling

River

cooling

Reuse of

heat Solar Wind

Indirect Air-to-air

cooling

Direct Air

Cooling Free Cooling

Google, Hamina X X X

KPN. Haarlem X X

Rabobank, Boxtel X X X

T-Systems,

Magdenburg X X X

University Medical Centre

Groningen

X X

University of Utrecht

X X

Curacao data

centre X

Equinix,

Amsterdam X X

Facebook, Sweden

X X

Facebook Altoona, USA

X X

Facebook

Prineville, USA X X X

Atos data centre

Helsinki X

District Heating System

Rabobank Best X X

Interconnect,

Amsterdam X

ING, the

Netherlands X

Data center group, the

Netherlands

X X

ING Roosendaal X X

Telecity London X

Data centres in

Helsinki, Finland X

District Heating System

Avalon networks,

Germany X

German web hosting providers

X Purchase X Purchase



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7.2 CONCRETE EXAMPLES OF DATA CENTRES

KPN Data Centre (Haarlem, the Netherlands)

The applied cooling concept is based on a rotary heat wheel, providing a very

effective, simple and robust means of cooling the data centre. Main

characteristics:

White space size 1.800m2

White space temperature 24˚C

HVAC N+2

Powerfeets 2N

UPS 2N

Generators N+1

220 & 400V AC

Figure 7-1 KPN data centre, Haarlem

Google Data Centre (Hamina, Finland)

A unique high-tech cooling system is being used, where only sea water from the

Bay of Finland is cooling the data centre [85].



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Figure 7-2 Google data centre in Hamina, Finland [85]

Rabobank Data Centre (Boxtel, the Netherlands)

ATES to heat the office buildings next door and to provide extra cooling when

needed during the summer. The ATES is filled with waste heat and free cooling.

When a person is not present, the lights will shut off, implying a lights out

principle. Heating and cooling of the office complex using residue heat from the

data centre.

Figure 7-3 Rabobank data centre Boxtel

T-Systems Data Centre (Magdenburg, Germany)

Indirect air-to-air cooling, the waste heat of the data centre is used for the

heating of the secondary buildings on site. When construction completed this will

be the largest data centre of Germany with a size of 150.000 m2.



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Figure 7-4 T-Systems Data Centre in Magdenburg

University Medical Centre (Groningen, the Netherlands)

Indirect air-to-air cooling. Combined central electrical systems with neighbour

laboratory. Main characteristics:

500 m2 white space

2,000 W/m2

1 MW IT power

Indirect air to air cooling

Figure 7-5 University Medical Centre Groningen



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University of Utrecht (Utrecht, the Netherland)

Increased energy efficiency by using an active power static-UPS system with

flywheels, using free cooling with hybrid coolers and connection to thermal

aquifer system. Main characteristics:

White Space 256m2 (Day-1 Power 360kW , End situation 720kW)

Gross floor plant areas (in basement) 600m2

Total ground floor area (Electrical systems + generators) 600m2

Total gross floor area 1.200m2

Roof area 1.200m2

Redundancy feeds N (10kV)

Power systems 2N

Generators N

UPS = 2N (UPS , back-up Flyweels)

Redundancy cooling N+1

Figure 7-6 University Utrecht

Equinix Data Centre (Amsterdam, the Netherland)

Tapping ground water in an Aquifer Thermal Energy Storage (ATES) system [86].

Main characteristics:

Data floor 3.400 m2

Gross 5.500m2

Electrical Capacity – 1.8 kVA/m2 (4.5 kVA per cabinet average)

UPS Configuration – AC supply: Static UPS System with up to 6x 30 kVA in

N+1 per string. 5 strings available - 10 minutes of autonomy on full load



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UPS Topology – N+1

# of Utility Feeders – 2

# of Power Transformers – Five transformers at 2 MVA per feed + 1 swing

feed at 2 MVA

Utility Voltage – 10 kV

Power Feeds – 2x 10 MVA medium voltage, 10 kV utility supply

Power On-site – 230 V one phase AC or 400 V three phase AC

Generators – N+1 configuration - 2.1 MVA each. 1 generator per feed. 5

feeds available + 1 swing feed. 48 hours on-site fuel autonomy (120 m3),

refuelable during use

Standby Power – 6x 2.1 MVA

Standby Power Config. – N+1 conform distributed redundancy model

Lighting – High frequency, minimal 300 Lux

Cooling Capacity – Up to 2 kW/m² (6826 BTUH)

Cooling Plant – Cooling towers in N+1. Chillers in N+1. Cooling circuits in

2N. CRAC-units in N+1.

Figure 7-7 Equinix data centre Amsterdam



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Facebook Data Centre (Luleå, Sweden)

Water energy from Dams in the Luleå river.

Figure 7-8 Facebook Luleå

Facebook Data Centre (ltoona, USA)

Wind energy by a wind project located less than two hours away. The data centre

is 100% carbon neutral according to Facebook [87] .

Figure 7-9 Facebook Altoona

Rabobank Best Data centre (the Netherlands)

ATES and free cooling. Main characteristics:

White space area: 6.000 m2 divided over two floors.

Building is realised in an old letter production and office facility with little

free space. Roughly 10.000 m2 or parking area is available that could be

used for solar panels

A fusion concept is used for the power supply. This means that there is a

static UPS feed and a DRUPS power feed.



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Figure 7-10 Rabobank, Best

Interconnect (Eindhoven, the Netherlands)


Established in 2011, designed as a Data Centre with own parking area.

3,000m2 which can be expanded to 6.000m2.

Power: 10 MW, separate A- and B-feeds, each feed has its own UPS,

generator and transformer available. There is also a third power feed to

maintain redundancy during maintenance work.

Cooling: Up to 10 kW per rack, based on cold corridor and direct free

cooling.

Interconnect Data Centre Den Bosch (Hertogenbosch, the Netherlands)


Established in 2005/2006, designed as a data center with an own parking

area.

Power: 1 MW, separate A- and B-feeds, each feed has its own UPS,

generator available.

Cooling: Up to 10 kW per rack, based on cold corridor and free cooling (all

at least N+1)

Facebook Data Centre (Prineville, USA)

Solar energy, direct air cooling [88]. This results in a data centre that requires

52% less energy to operate than a comparable facility built to code requirements



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Figure 7-11 Facebook Prineville

Telecity Data Center (West-London, UK)

Free cooling chillers

Figure 7-12 Telecity Data Centre West London, UK

ING (Roosendaal, the Netherlands)

Direct air free cooling

Atos Data Centre (Helsinki, Finland)

Sea water cooling, the servers is fed into the municipal heating network [89].

7.3 VARIOUS OTHER USE OF RENEWABLES WITHIN DATA CENTRES

In Helsinki, several data centres are connected to the district cooling network

where the chilled water is produced with a renewable share of 60 % (e.g. cold

sea water) [91] . The heat from the data centres is transferred to the district

heating network and used for heating buildings and domestic water.



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The German web hosting provider Avalon satisfies 20 % of its power demand by

their own PV field, the remaining 80 % are green electricity which is purchased

[92].

Almost all German web hosting providers are running their data centres with

green electricity (majorly hydropower, but also wind and solar power) supplied

by outside companies [93].

The stylish tech giant has long been committed to reducing its environmental

impact, as it fulfils 3 of their needs: reducing costs, reducing impact on the

environment and rehabilitating its green image which has been tarnished by

various news stories. 3 of Apple’s data centres now run on 100% renewable

energy (Maiden NC, Newark CA and Prineville OR) and their efforts are so great

that the largest nonutility solar and fuel cell installations in the US are Apple’s.

The solar power at Apple’s Maiden facility ensures that during peak hours its

energy come from renewable sources. To ensure energy security in case of a loss

of power on the grid, their biogas fuel cells provide a vital safety net to prevent

loss of supply to essential systems. Of course the story is slightly more

complicated than it appears with Apple in some cases buying from non-

renewable sources and then offsetting that elsewhere. [94]

To reduce the fresh water consumption, Google equipped two of its data centres

with system that use a 100% recycled water. Google is also working on systems

to collect the rain water to cool a third data centre. The idea is very simple,

instead of using drinkable water for the cooling systems, non-drinkable water is

used and filtered up to the point that is acceptable for the cooling systems.

Within the two data centres, water of different sources is used. In Douglas

County, the city waste water is used, while within the Belgian Facility water from

an industrial canal is used. Here a large tank, filled with fine sand is used to filter

small particles from the water which results in clear, although non drinkable

water. Although it is not always profitable to use recycled water, Google remains

optimistic in relation to finding durable solutions for a large part of their water

consumption. [95]

In June this year Google said it had entered a deal with German insurance

company Allianz and Swedish wind-farm developer O2 to provide wind power for

the facility for ten years from September 2015, using a wind farm in Northern

Sweden providing 72MW of power. [96]

http://www.datacenterdynamics.com/focus/archive/2013/06/google-buys-wind-power-finland-data-center

http://www.datacenterdynamics.com/focus/archive/2013/06/google-buys-wind-power-finland-data-center



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8 CONCLUSIONS

The incorporation of on-site renewable energy sources to satisfy the high energy

demand of Data Centres is not sufficient, since this energy production is highly

dependent on the space available in the Data Centre building which is usually

really small. Therefore there is a limitation of the energy capacity

installed/produced mainly for solar and wind energy. A first step before the

installation of renewable energy sources is the implementation of energy

efficiency measures to reduce the electrical consumption and the cooling

demand.

Once the consumption has been reduced with the mentioned energy efficiency

measures, Data Centres operators have basically two options to deal with

renewable energy: either they generate their own renewable energy or they

decide to buy it to a third party through different legal instruments. In the case

of buying it from third-party suppliers, the different energy mixes of European

countries have to be taken into account, as we have seen in chapter 3. For

example, when installing a Data Centre, it can be easier to find adequate prices

from third party renewable energy supply in certain countries with high

renewable energy penetration in the electricity mix (like Sweden or Spain) than

in countries with much lower renewable energy penetration (like Italy). In any

case, it is important to see the variability of this penetration, and its likeliness to

evolve rapidly in the near future, as well as the need of regular revisions of its

values in regulations. As far as on-site or off-site renewable energy production,

there are a vast variety of technologies that can be used, either to produce

electricity alone, cooling alone [50] or to produce at the same time electricity

and cooling. This document shows all the possibilities with a holistic perspective,

though in future deliverables, the most promising schemes will be pointed out.

It is noticed that most of the examples of renewable energy technologies applied

to real Data Centres only focus on the improvement of the HVAC part of the

energy demand, but it is very important to understand that a high portion of the

demand is mainly electrical. An essential effort has, thus, to be put during

RenewIT project to analyse the coverage of the purely electrical part of the

consumption with renewable energy supply, either with local resources or with

the combination of HVAC renewable energy technologies and third party

renewable electricity supply. This will be the only way to reach for Nearly Zero

Energy Data Centres.



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Deutschland,” Agentur für Erneuerbare Energien e.V., 2010.

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of 159

ANNEX 1. DETAILED RENEWABLE ENERGY

RESOURCE DATA ANALYSIS FOR DIFFERENT

LOCATIONS

In the present annex, comparable figures are provided for visualising the

potential of solar radiation, wind speed and air temperature. They consist of

three charts giving the following information:

a) Daily mean value during the year (daily sum for solar radiation): This

chart illustrates the differences between the availability of the resource in

summer and in winter. Fluctuations from one day to the next can also be

assessed.

b) Duration curve: This chart shows for how many hours a certain value of

irradiation, wind speed or air temperature is reached or exceeded during

the year.

c) Hourly mean value (sum for solar radiation) during three days: The

fluctuation of the resource during three days in winter and in summer can

be seen. For winter, the period from 20th to 22nd January is shown while

the days for summer are selected for each location in the following way:

o solar radiation: the day with the highest sum of solar radiation is

shown in the middle of the period (occurs in June or July)

o wind: period from 20th to 22nd July

o air temperature: the day with the highest daily mean value is shown

in the middle of the period (occurs in July or August)

The charts were created from Meteonorm data [97] which represent typical years

at the particular locations.



of 159

SPAIN

Solar energy

The annual global irradiation in Spain is higher than in almost all other European

countries. The mean global irradiation2 is 1,600 kWh/m²a, some regions in

Southern Spain receive 2,000 kWh/m²a [98] [99]. Thus, there is an enormous

available potential for power generation which has been estimated to 3,000

TWh/a each from PV systems and from concentrating systems. In 2020, 12 TWh

and 14 TWh of power could be generated by PV and concentrating systems,

respectively [99]. Additionally, 170 TWh of solar heat are available whereof 7

TWh could be harnessed in 2020.

As the sun chart in Figure A0-1 shows for the example of Barcelona, the sun

reaches relatively large elevation angles even in spring and in autumn. Thus,

usable solar radiation is available year-round as visualised by Figure A0-2 a) and

c). The highest potential of solar radiation is available from April to September;

the annual global irradiation sums to 1,600 kWh/m². From subfigure b) it can be

seen that global radiation to horizontal surfaces exceeds 400 W/m² for more

than 1,800 hours. About 60 % of the solar irradiation is direct radiation and thus

available for harnessing with concentrating technologies.

Figure A0-1 Sun chart for Barcelona, Spain

2 The irradiation data presented here refer to horizontal surfaces. With optimal tilt angles

of PV modules/thermal collectors or even tracking systems, more energy can be

harnessed.

-120 -90 -60 -30 0 30 60 90 1200

20

40

60

80

Solar azimuth angle [°]

Sola

r ele

vation a

ngle

[°]

December

March/September

June



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Wind energy

Wind power has a significant potential in Spain. The available potential of

onshore and offshore wind power is estimated to 780 TWh/a [99]. In 2020, 72

TWh and 2 TWh of power could be generated onshore and offshore, respectively.

Figure A0-3 shows that wind speed at the reference location of Barcelona goes

up and down during the whole year. The annual average of the wind speed in a

height of 10 m amounts to 2.7 m/s.

Figure A0-2 Availability of solar energy in Barcelona [97]

Jan 1 Mar 1 May 1 Jul 1 Sep 1 Nov 1 Dec 310

2

4

6

8

10

Day

Sola

r ra

dia

tion [

kW

h/m

2d]

a) Daily sum of solar radiation to a horizontal surface during the year

direct

global

0 1000 2000 3000 4000 5000 6000 7000 80000

200

400

600

800

1000

Duration [h]

Sola

r ra

dia

tion [

W/m

2]

b) Duration curve of solar radiation to a horizontal surface

direct

global

0 6 12 18 24 30 36 42 48 54 60 66 720

500

1000

Time [h]

Sola

r ra

dia

tion [

W/m

2]

c) Intensity of solar radiation (horizontal surface) during three days in January and July

direct Jan global Jan direct Jul global Jul



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Figure A0-3 Availability of wind energy (wind speed at 10 m above ground) in Barcelona, Spain

[97]


5

10

15

Day

Win

d s

peed [

m/s

]

a) Daily mean value of wind speed during the year

0 1000 2000 3000 4000 5000 6000 7000 80000

5

10

15

Duration [h]

Win

d s

peed [

m/s

]

b) Duration curve of wind speed

0 6 12 18 24 30 36 42 48 54 60 66 720

5

10

15

20

Time [h]

Win

d s

peed [

m/s

]

c) Hourly mean value of wind speed during three days in January and July

Jan

Jul



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Biomass

In 2000, the available energy potential of biomass has accounted for 120 TWh

from the different resources shown in Figure A0-4 [37]. The prospective available

potential is estimated to 310 TWh whereof in 2020, 12 TWh of power and 54

TWh of heat could be produced [99].

Figure A0-4 Spanish biomass energy resources in 2000 (total: 120 TWh) [37]

Geothermal energy

Spain has a significant potential of geothermal energy estimated to 300 TWh,

mainly from dry (petrothermal) and low-enthalpy resources [99]. In 2020, 0.3

TWh of power and 0.1 TWh of heat could be generated from geothermal energy.

Additionally, 5 TWh of geothermal heat could be harnessed by heat pumps.

Marine energy

The potential of marine energy at the Spanish coasts is estimated to 5 TWh and

essentially limited to wave power [99]. In 2020, 0.2 TWh of power could be

generated from waves.

Environmental energy

In Figure A0-5, dry-bulb and wet-bulb air temperatures in Barcelona are shown.

The variation of daily mean values between summer and winter amounts to

about 25 K. Temperature differences between day and night are about 5 to 10 K

both in winter and in summer.

Figure A0-5 b) shows that dry-bulb and wet-bulb temperatures lower than 15 °C

are available for 4,000 and 5,400 hours, respectively.

Sea water for cooling is available in Spain along the coasts of the Atlantic and the

Mediterranean Sea.



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Figure A0-5 Availability of ambient air for free cooling in Barcelona, Spain [97]

Jan 1 Mar 1 May 1 Jul 1 Sep 1 Nov 1 Dec 31-10

0

10

20

30

Day

Tem

pera

ture

[°C

]

a) Daily mean value of air temperature during the year

w et-bulb

dry-bulb

0 1000 2000 3000 4000 5000 6000 7000 80000

10

20

30

Duration [h]

Tem

pera

ture

[°C

]

b) Duration curve of air temperature

w et-bulb

dry-bulb

0 6 12 18 24 30 36 42 48 54 60 66 72

0

10

20

30

40

Time [h]

Tem

pera

ture

[°C

]

c) Air temperature during three days in January and August

w et-bulb Jan dry-bulb Aug w et-bulb Jan dry-b. Aug



of 159

GERMANY

Solar energy

The annual global irradiation in Germany totals 900 to 1,200 kWh/m² which is

enough to contribute to power and heat production considerably. In 2020, 40

TWh of power and 30 TWh of heat could be generated [100].

As the sun chart in Figure A0-7 shows for the example of Chemnitz, the sun

reaches only a small elevation angle and covers a small azimuth angle range

during winter. Thus, little solar radiation is available in winter as visualised by

Figure A0-6 a) and c). The highest potential of solar radiation is available from

May to August; the annual global irradiation sums to 1,120 kWh/m². From

subfigure b) it can be seen that global radiation to horizontal surfaces exceeds

400 W/m² for about 1,000 hours. Slightly less than 50 % of the solar irradiation

is diffuse and thus cannot be harnessed with concentrating technologies.



of 159

Figure A0-6 Availability of solar energy in Chemnitz, Germany [97]


2

4

6

8

10

Day

Sola

r ra

dia

tion [

kW

h/m

2d]


direct

global

0 1000 2000 3000 4000 5000 6000 7000 80000

200

400

600

800

1000

Duration [h]

Sola

r ra

dia

tion [

W/m

2]


direct

global

0 6 12 18 24 30 36 42 48 54 60 66 720

500

1000

Time [h]

Sola

r ra

dia

tion [

W/m

2]

c) Intensity of solar radiation (horizontal surface) during three days in January and June

direct Jan global Jan direct Jun global Jun



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Figure A0-7 Sun chart for Chemnitz, Germany

Wind energy

Wind power has a high potential in central and northern Germany. In 2020, 112

TWh could be generated onshore. The 2020 offshore potential on the North Sea

and the Baltic Sea amounts to 37 TWh [100].

Figure A0-9 shows wind availability at the reference location of Chemnitz. The

annual average of the wind speed in a height of 10 m amounts to 3.4 m/s.

Biomass


from the different resources shown in Figure A0-8 [37]. In 2020, 54 TWh of

power and 150 TWh of heat could be produced from biomass [100].

Figure A0-8 German biomass energy resources in 2000 [37]

-120 -90 -60 -30 0 30 60 90 1200

20

40

60

80


Sola

r ele

vation a

ngle

[°]

December

March/September

June



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Figure A0-9 Availability of wind (wind speed at 10 m above ground )energy in Chemnitz, Germany

[97]


5

10

15

Day

Win

d s

peed [

m/s

]


0 1000 2000 3000 4000 5000 6000 7000 80000

5

10

15

Duration [h]

Win

d s

peed [

m/s

]


0 6 12 18 24 30 36 42 48 54 60 66 720

5

10

15

20

Time [h]

Win

d s

peed [

m/s

]


Jan

Jul



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Geothermal energy

95 % of the geothermal energy potential in Germany is petrothermal, i.e. dry

[100]. As shown in Figure A0-10 a), the reservoirs are mainly located in the

south and the east of Germany while hydrothermal sources are available in

Northern Germany (see Figure A0-10 b). In 2020, 4 TWh of power and 42 TWh

of heat (including heat pumps) could be generated from geothermal energy.

Figure A0-10 Geothermal resources in Germany [100]

Marine energy

The German potential of tidal and wave power as well as salinity gradient energy

is very low and will not be used commercially within the next decade [101].


In Figure A0-11, dry-bulb and wet-bulb air temperatures in Chemnitz are shown.

The variation of daily mean values between summer and winter amounts to more

than 35 K. In summer, temperature differences between day and night are

higher (ca 10 K) than in winter (< 5 K). Thus, even if the day-time air

temperature is too high for free cooling, it might be cold enough during the

night.

Figure A0-11 b) shows that dry-bulb and wet-bulb temperatures lower than 15

°C are available for 6,000 and 7,300 hours, respectively.

Sea water for cooling is only available at the North German coast. The average

temperature of the North Sea varies between 6 °C in winter and 17 °C in

summer [102].

The temperature of superficial groundwater in Germany is generally between 8

and 12 °C but can be higher under city centres [103].



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Figure A0-11 Availability of ambient air for free cooling in Chemnitz, Germany [97]


0

10

20

30

Day

Tem

pera

ture

[°C

]


w et-bulb

dry-bulb

0 1000 2000 3000 4000 5000 6000 7000 80000

10

20

30

Duration [h]

Tem

pera

ture

[°C

]


w et-bulb

dry-bulb

0 6 12 18 24 30 36 42 48 54 60 66 72

0

10

20

30

40

Time [h]

Tem

pera

ture

[°C

]

c) Air temperature during three days in January and July

w et-bulb Jan dry-bulb Jan w et-bulb Jul dry-bulb Jul



of 159

NETHERLANDS

Solar energy

The annual global irradiation in the Netherlands is about 1,000 kWh/m² and thus

allows significant power and heat production. By 2050, the potential for power

and heat production is estimated to 76 TWh and 8 TWh, respectively [104]. In

2020, 0.6 TWh of power and 0.3 TWh of heat could be generated [105].

The sun chart in Figure A0-13 shows for the example of Amsterdam that during

winter, the sun reaches only a small elevation angle and covers a small azimuth

angle range. Thus, little solar radiation is available in winter as visualised by


May to August; the annual global irradiation sums to 980 kWh/m². From


400 W/m² for about 850 hours. Nearly 60 % of the solar irradiation is diffuse and

thus cannot be harnessed with concentrating technologies.



of 159

Figure A0-12 Availability of solar energy in Amsterdam, Netherlands [97]


2

4

6

8

10

Day

Sola

r ra

dia

tion [

kW

h/m

2d]


direct

global

0 1000 2000 3000 4000 5000 6000 7000 80000

200

400

600

800

1000

Duration [h]

Sola

r ra

dia

tion [

W/m

2]


direct

global

0 6 12 18 24 30 36 42 48 54 60 66 720

500

1000

Time [h]

Sola

r ra

dia

tion [

W/m

2]





of 159

Figure A0-13 Sun chart for Amsterdam, Netherlands

Wind energy

Wind power has a high potential in the Netherlands, but onshore use is restricted

by available land area. Thus, the offshore potential is particularly interesting. By

2050, 130 TWh/a of power could be generated offshore at the North Sea in

addition to 20 TWh/a onshore [104]. In 2020, 13 TWh and 19 TWh could be

harnessed onshore and offshore, respectively [105].

Figure A0-15 shows wind availability at the reference location of Amsterdam. The


Biomass

In 2000, the available energy potential of biomass accounted for 33 TWh from

the different resources shown in Figure A0-14 [37]. By 2050, 44 TWh/a of

domestic biomass could be available while further heat and power generation

relies on imports of biomass [104]. In 2020, 17 TWh of power and 18 TWh of

heat could be produced from biomass [105].

Figure A0-14 Dutch biomass energy resources in 2000 (total: 33 TWh) [37]

-120 -90 -60 -30 0 30 60 90 1200

20

40

60

80


Sola

r ele

vation a

ngle

[°]

December

March/September

June



of 159

Figure A0-15 Availability of wind (wind speed at 10 m) energy in Amsterdam, Netherlands [97]

Geothermal energy

Eligible geothermal resources in the Netherlands are mainly aquifers

(hydrothermal resources) at the locations shown in Figure A0-16.


5

10

15

Day

Win

d s

peed [

m/s

]


0 1000 2000 3000 4000 5000 6000 7000 80000

5

10

15

Duration [h]

Win

d s

peed [

m/s

]


0 6 12 18 24 30 36 42 48 54 60 66 720

5

10

15

20

Time [h]

Win

d s

peed [

m/s

]


Jan

Jul



of 159

The potential of geothermal energy is quite uncertain. By 2050, 36 TWh/a could

be available including heat harnessed by means of heat pumps [104]. In 2020,

each 3 TWh of heat could be produced both directly and via heat pumps [105].

Figure A0-16 Geothermal resources in the Netherlands [106]

Marine energy

The Netherlands have a very low potential of wave energy and a relatively low

potential of tidal energy. However, the theoretical potential of salinity gradient

energy is relatively high with an estimation of 16 TWh/a [107]. By 2020, marine

energy is not yet expected to play a considerable role in Dutch power and heat

generation [105].


In Figure A0-17, dry-bulb and wet-bulb air temperatures in Amsterdam are

shown. Daily mean values vary by more than 20 K between summer and winter.

In summer, temperature differences between day and night are higher (ca 10 K)

than in winter (< 5 K). Thus, even if the day-time air temperature is too high for

free cooling, it might be cold enough during the night.



Sea water for cooling is available at the Dutch coast. The average temperature of

the North Sea varies between 6 °C in winter and 17 °C in summer [102].

The temperature of superficial groundwater in the Netherlands is generally

between 9 and 12 °C [108]. A lot of systems are existing which use aquifers as

heat and cold storages.



of 159

Figure A0-17 Availability of ambient air for free cooling in Amsterdam, Netherlands [97]

SWEDEN

Solar energy

The annual global irradiation in Sweden adds up to 1,000 kWh/m² in the south

and 800 kWh/m² in the north [109]. By 2050, 10 TWh/a of heat and 5 TWh/a of


0

10

20

30

Day

Tem

pera

ture

[°C

]


w et-bulb

dry-bulb

0 1000 2000 3000 4000 5000 6000 7000 80000

10

20

30

Duration [h]

Tem

pera

ture

[°C

]


w et-bulb

dry-bulb

0 6 12 18 24 30 36 42 48 54 60 66 72

0

10

20

30

40

Time [h]

Tem

pera

ture

[°C

]





of 159

power could be generated even in the Northern European country [110]. In

2020, each 4 TWh of power and heat could be harnessed [111].

The sun chart in Figure A0-19 shows for the example of Luleå that the sun’s path

along the sky is very short during winter due to the location close to the Arctic

Circle. Thus, solar radiation is almost not available in winter as visualised by


June to August, the annual global irradiation sums to 870 kWh/m². From


400 W/m² for about 750 hours. About 50 % of the solar irradiation is diffuse and

thus cannot be harnessed with concentrating technologies.



of 159

Figure A0-18 Availability of solar energy in Luleå, Sweden [97]


2

4

6

8

10

Day

Sola

r ra

dia

tion [

kW

h/m

2d]


direct

global

0 1000 2000 3000 4000 5000 6000 7000 80000

200

400

600

800

1000

Duration [h]

Sola

r ra

dia

tion [

W/m

2]


direct

global

0 6 12 18 24 30 36 42 48 54 60 66 720

500

1000

Time [h]

Sola

r ra

dia

tion [

W/m

2]





of 159

Figure A0-19 Sun chart for Luleå, Sweden

Wind energy

Wind power has a high potential in Sweden. It is estimated that 58 TWh/a of

power could be generated by 2050 at onshore and offshore locations [110]. In

2020, 20 TWh and 10 TWh could be generated onshore and offshore,

respectively [111].

Figure A0-21 shows wind availability at the reference location of Luleå. The


Biomass


from the different resources shown in Figure A0-20 [37]. In 2020, 17 TWh of

power and 110 TWh of heat could be produced from biomass [105].

Figure A0-20 Swedish biomass energy resources in 2000 (total: 92 TWh) [37]

-120 -90 -60 -30 0 30 60 90 1200

20

40

60

80


Sola

r ele

vation a

ngle

[°]

December

March/September

June



of 159

Figure A0-21 Availability of wind (wind speed at 10 m) energy in Luleå, Sweden [97]


5

10

15

Day

Win

d s

peed [

m/s

]


0 1000 2000 3000 4000 5000 6000 7000 80000

5

10

15

Duration [h]

Win

d s

peed [

m/s

]


0 6 12 18 24 30 36 42 48 54 60 66 720

5

10

15

20

Time [h]

Win

d s

peed [

m/s

]


Jan

Jul



of 159

Geothermal energy

Generally, the geothermal temperature gradient is relatively low in Sweden

[112]. Thus, electricity generation is not feasible at present. Some potential for

direct heat production is available at certain locations e.g. in Skåne County

(Southern Sweden), but it is not considered in the planned heating and cooling

energy supply in 2020 [105]. However, a significant amount of heat is produced

by means of geothermal heat pumps in Sweden.

Marine energy

Wave energy could deliver a significant contribution to power generation by

2020, but it is difficult to estimate. The long-term potential is estimated to at

least 10 GWh [111].


In Figure A0-22, dry-bulb and wet-bulb air temperatures in Luleå are shown. The

variation of daily mean values between summer and winter amounts to about

35 K. In summer, temperature differences between day and night are higher (ca

10 K) than in winter (ca 5 K). Thus, even if the day-time air temperature is too

high for free cooling, it might be cold enough during the night.



Sea water for cooling is available along the Swedish coast. The average

temperature of the Baltic Sea varies between 2 °C in winter and 16 °C in

summer [113].

The temperature of superficial groundwater in Sweden is generally between 4

and 12 °C [114].



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Figure A0-22 Availability of ambient air for free cooling in Luleå, Sweden [97]


0

10

20

30

Day

Tem

pera

ture

[°C

]


w et-bulb

dry-bulb

0 1000 2000 3000 4000 5000 6000 7000 80000

10

20

30

Duration [h]

Tem

pera

ture

[°C

]


w et-bulb

dry-bulb

0 6 12 18 24 30 36 42 48 54 60 66 72

0

10

20

30

40

Time [h]

Tem

pera

ture

[°C

]



deliverable d4.1 report of different options for renewable ...figure 4-2 annual sum of global...

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