Thursday 28th and Friday 29th September 2006

Imperial College London, South Kensington Campus, London SW7 2AZ

Decentralised Energy Systems

Matthew Leach(contributions from Adam Hawkes)

m.leach@imperial.ac.ukwww.iccept.ic.ac.uk

© Imperial College London

Imperial College Centre for Energy Policy and Technology

Imperial CollegeLondon

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ICEPTDirector: Professor Peter Pearson

Deputy Director: Dr Matthew LeachMissionResearch & policy advice at interface of energy policy & technology

An Interdisciplinary CentreCollaborating with Imperial’s Energy Futures Lab and with UK & international researchers

OutputsResearch findingsEvidence-based technology & policy reviewPostgraduate training

• strong PhD programme• MSc in Environmental Technology: Energy Policy Option

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Presentation outline

• What is Decentralised Energy?

• Decentralised Energy at Imperial

• Why interest in DE?

• ICEPT’s work: illustrative examples on micro-CHP

• Conclusions

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Source: based on Ofgem(2002)

Conventional power system

Industrial consumers

Residential consumers

Distribution network

Central power producers

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With decentralised energy

Active distribution

network

+ cogeneration =>consumers &

producers

+ microgeneration=>consumers &

producers

Source: based on Ofgem(2002)

+ embedded generation

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Importance of networks, components and people

One vision of the future of power systems (analogy to internet evolution:-

Source: Rebecca Willis. grid 2.0 the next generation. Green Alliance, 2006

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Decentralised Energy componentsSource: adapted from Mariyappan (2003)

(a) Power/heat conversion (both grid-connected and off-grid…)

Fossil fuelled (some with potential for bio-fuel substitutes)• Relatively large scale, conventional technology, eg:

– Combined-Cycle Gas Turbine (35 MW – 400 MW)– Internal Combustion Engines (5 kW – 10 MW)

• Smaller scale, eg:– Stirling Engine (1 kW – 10 kW) – Microturbines (35 kW – 1 MW)

• Fuel Cells: Solid Oxide or Proton Exchange (250kW– 5MW; 1kW–250kW)

Renewables, eg:• Small Hydro; Micro Hydro (1 MW – 100 MW; 25 kW – 1 MW)• Wind Turbines(200 Watt – 5 MW, to GW arrays)• Photovoltaic Arrays (20 Watt – 100 kW)• Biomass, e.g. based on gasification (100 kW – 20 MW)

(b) Energy storage devices

(c) Demand side: information systems, intelligent control

(d) Associated infrastructures (notably active electricity distribution networks)

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Decentralised Energy at Imperial• Strong technology programmes in many departments (eg Fuel Cells, PV,

wind, bioenergy, waste-to-energy, …)

• Department of Electrical and Electronic Engineering: strong group on power system control, DG integration and future of networks

• Centre for Energy Policy and Technology (ICEPT): focus on techno-economic, environmental and policy analyses of emerging energy options (eg H2, fuel cells, bioenergy, building integrated and off-grid renewables, and decentralised energy specifically)

• Particular areas of interest to ICEPT– Modelling approaches, and sensitivities of optimum design to economic, market and

environmental factors– Demand-Side participation– Micro-Grids and community heat networks– Small scale waste to energy systems (eg contacts with Ebara corp gasification)– Valuation and risk-management of decentralised energy investments– Transitions to DG power systems and scenarios– Policy aspects

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Why interest in Decentralised Energy (globally)?• Technology

– New, smaller, conversion devices– Can help overcome T&D network constraints– Stimulate development of ‘active’ networks

• Environment, economics– Some options inherently low carbon (eg renewables)– Can facilitate use of cleaner fuels (eg local wastes or biomass)– Avoidance of transmission losses– Opportunity to capture ‘waste’ heat for local heat loads– Facilitate closer end-user engagement with energy– Contribution to wider transition to low carbon future…

• Economics, commercial– Low capital, fast revenue stream = lower risk modular investments– Value of flexibility, adaptability and diversity in a competitive market– Integration of electricity, gas & heat suppliers/markets– Underlying need for new power investments, globally

• Security of supply– Possible improvement in power quality and security of local supply

*

*

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Power generation conversion losses

Gas to heat houses

Gas

Elec.

Petrol.

Industry

Transport

Resident.

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WADE (2003)

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Constraints facing Decentralised Energy (in UK)• Current market structures and rules

• Some high technology costs

• High gas prices

• Planning and connection constraints and public perceptions

• Network integration: capacity to accept is limited and not always where needed

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Growth in electricity generation from renewable sources since 1990 (Source: adapted from DUKES 2002 – 2005)

2015

1515

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Market size - Global DG capacity (< 10 MW) by market segment

• Possibly very significant shift in emphasis on the part of utilities to distributed power

• Large DG growth expected in industrial applications and extended electrification

• DG penetration in commercial and residential is lower, but characterised by a large number of smaller units

Key Findings

Source: Imperial College / E4tech Ltd

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

2005 2010 2015 2020

Cap

acity

[GW

]

Shift away from centralisedpower by utilities

Extended electrification tooff-grid locations

Residential / communityapplications

Commercial applicationsIndustrial applications<10MW

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Residential Micro-CHP

• Stirling engine, ICE, Solid Oxide Fuel Cell, PEM Fuel Cell

Source: WhisperGen

Source: Hexis

Source: Ballard

Source: Baxi

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System Diagram

Fuel Conditioner

Solid Oxide Fuel Cell

Afterburner (burns

excess fuel)

Heat Recovery System

Electrical Load

Hot Water

Storage&

extra Boiler

Heat Load

Fuel Input

Fuel Flow

Heat/power Flow

Grid PowerLosses

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Stack and BOP model

Water

Anode side

Cathode sideBurner

Steam generator

+

Power

3 phase AC

MixerFuel feed

Exhaust gas

Air blower

Air feed

Air pre-heater

Waste heat recovery

3 phase AC

Mixer

Air blower

Fuel pre -heater

Cooling waterHot water

Pre-reformer

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Optimisation Model Applications

• How to model residential CHP applications

• Key economic drivers for SOFC-based technology

• Influence of ramp constraints on economic and environmental outcomes

• Synthesise a least cost operating strategy

• How best to meet thermal demand (eg value of thermal storage)

• Capacity credit of micro-CHP: % of installed capacity that will reliably reduce peak system demand

• Relative performance of micro-CHP and community scale

• (Next) Influence of changing patterns of thermal demand

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Input data time-step assumptionsHourly Data Five Minute Data

0 5 10 15 20 250

20

40

60

80

100

120

140

time (hours)

Pow

er D

eman

d (k

Wh)

Electrical Power Demand

0 5 10 15 200

5

10

15

20

25

30

time (hours)P

ower

Dem

and

(kW

h)

Electrical Power Demand

Carbon emissions reduction is overestimated by analyses using coarser temporal precision by up to 50%, and economic case overestimated by around 10%.

Coarser precision overestimates export of low-carbon electricity, and underestimates import of high-carbon grid power.

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SOFC for DG in UK

• Ceres Power, a SOFC tech. company (& Imperial spin-out) recently won the Carbon Trust innovation award in the UK.

• SOFC has the potential for a relatively low cost/kW installed

• Fuelled by natural gas or hydrogen rich fuel

• Carbon-efficient technology, very low NOx, very low SOx

• Research underway across the capacity range (1kW – 1MW)

Sensitivity of optimum system size to installed cost per kW

Cost-optimal size for residential applications is roughly 0.5 kWe, for capital cost of £800/kWe

200 400 600 800 1000 1200 1400 16005000

5500

6000

Lifetime Cost (£)

SOFC base cost per kW installed (£/kW)200 400 600 800 1000 1200 1400 16000

1

2

3

4

5

6

Capacity (kW)

Optimum Generation Capacity of SOFC stack (kW)

Optimum (Minimum)Lifetime Cost of SOFC CHP system (£)

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DG generally has environmental benefits, but modelling helps reveal perverse effects…

If heat can be wasted to exhaust by micro-CHP, then it is often economically optimal to generate electricity to meet onsite loads and export to the grid, and to dump some of the heat generated. Wasted heat implies higher carbon emissions

Buyback Price vs CO2 Reduction for 1.1kW Stirling Engine (with 5kWh/h heat dump possible)

0

100

200

300

400

500

600

0 1 2 3 4 5 6Buyback Price (p/kWh)

CO

2 Em

issi

on A

void

ed (k

g) a

gain

st

Grid

/Boi

ler B

asel

ine

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Electricity Buyback (export) Prices

Current baseline cost

0 1 2 3 4 51250

1300

1350

1400

1450

1500

SOFC Stack Capacity (kWe)

MinimumAnnualised

cost (£) 0p/kWh2p/kWh4p/kWh

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Ramp Constraints

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.002 0.01 0.05 0.1 0.2 0.3 0.4 1

Rate of Change of Current Density Limit (A/cm2/min)

SOFC

Sta

ck C

apac

ity (k

We)

19.5

20

20.5

21

21.5

22B

oiler C

apacity (kW

th)Stack CapBoiler Cap

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Influence of thermal demands on micro-CHP

5 10 15 200

2000

4000

6000

8000

Time (Hours)

Spa

ce

Hea

t Dem

and

(kW

)

Case 1: Conventional Central Heating

5 10 15 200

2000

4000

6000

8000

Time (Hours)

Spa

ce

Hea

t Dem

and

(kW

)

Case 4: 3kW Underfloor Heating System

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Conclusions• Broadly, on DE

– Technology options are abundant, and improving– ‘System approach’ appropriate – demand/supply, infrastructures, people,

markets…Active networks and DSM will be an important aspect in future distribution network and DG penetration scenarios.

– Plenty of barriers: technical, market, regulatory, …

• Micro-CHP– Economic and environmental benefit… depending on…– Economics and environment aren’t everything. Space, quality of service,

etc– Rough and tough technology may be better than highly optimised

• Interesting questions:-– How do you quantify and model uncertainty in the new DE environment?

Eg portfolios, real options…– Technical and economic questions about infrastructure transition

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PublicationsA.D. Hawkes, P. Aguiar, C. A. Hernandez-Aramburo, M.A. Leach, N.P. Brandon, T.C.

Green, C.S. Adjiman (2006) "Techno-Economic Modelling of a Solid Oxide Fuel Cell Stack for micro-CHP" . Journal of Power Sources. Vol 156/2 pp 321-333

Castillo-Castillo A and Leach M (2006). Technology Scales and Types in Future Urban Waste Strategies: Is Compliance Sustainable and Feasible? In proceedings of ‘Waste 2006: Integrated Waste Management and Pollution Control Policy and Practice, Research and Solutions’, The Waste Conference Ltd, Warwick.

Hawkes A and Leach M (2005). Solid oxide fuel cell systems for residential micro-combined heat and power in the UK: Key economic drivers. Journal of Power Sources 149 72-83.

Hawkes A, Leach M, (2005). Impacts of temporal precision in optimisation modelling of micro-combined heat and power, Energy, Vol: 30, Pages: 1759 – 1779

Hawkes A and Leach M (2006). The Economic Value and Carbon Dioxide Emissions Implications of Community Heating Networks in the UK. 6th BIEE Academic Conference, St Johns College Oxford, September 20-21 2006. Submitted

Hawkes AD and Leach MA (June 2006 accepted). Cost Effective Operating Strategy for Residential Micro Combined Heat and Power, Energy

Hawkes A.D., Aguiar, P., Croxford, B., Leach, M.A., Adjiman, C.S., and Brandon, N.P. (September 2006 accepted ). Solid Oxide Fuel Cell Micro Combined Heat and Power System Operating Strategy: Options for Provision of Residential Space and Water Heating. Journal of Power Sources