2011 ctg038 a place in the sun photovoltaic electricity generation

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Sharing our experience

A place in the sunLessons learned from low carbon buildings

with photovoltaic electricity generation

enter



Contents

Sharing our experience 01

Photovoltaics 02

What are photovoltaic modules?

Why choose photovoltaics? 04

The benefits of photovoltaics

Assessing site feasibility 07

How to assess the suitability of your

site, including solar access, planning

and technology choices

Procurement and installation 11

Why gathering the right experience,

setting up contracts, team dynamics

and cost control matter

Ensuring best performance 14

Factoring metering and maintenance

into the earliest design stages

Most of the casestudy projects that

installed photovoltaicsare saving between5% and 10% carbonper year. They wouldstand to save £3,700per year through the

feed-in tariff

http://clients/CARBON%20TRUST/Current%20Jobs/12688%20Buildings%20accelerator%20programme/12892%20Metering%20and%20monitoring/Design/3_Layouts/12892%20Metering%20and%20monitoring.pdf

http://clients/CARBON%20TRUST/Current%20Jobs/12688%20Buildings%20accelerator%20programme/12892%20Metering%20and%20monitoring/Design/3_Layouts/12892%20Metering%20and%20monitoring.pdf



1A place in the sun

Sharing our experience: About this booklet

‘A place in the sun’ is part o the ‘Sharing our experience’

series. These booklets provide advice and tips to help

you to plan, build and manage cost-eective low carbon

buildings that really work to save you money and carbon.

The insights are based on real data rom 28 case

studies rom the Department o Energy and Climate

Change’s Low Carbon Buildings Programme and our

work on reurbishments. The projects cover many

sectors including retail, education, ofces and mixeduse residential buildings.

Further information

To find out how we can help with

your low carbon building project,

contact us on 0800 085 2005 or visit

www.carbontrust.co.uk/buildings

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2A place in the sun

Photovoltaics

Photovoltaic (PV) modules are panels o solar cells which convert sunlight intoDC electricity. This is then converted into the AC electricity used in buildings.

Site and orientation

PVs are reliable, low maintenance and silent.

They are an efficient source of zero carbon

electricity for new build and refurbishmentprojects. Ideally, PV arrays should be free from

shade, face within 45° of south and be inclined

at an angle of 30° of the horizontal plane.

Partially

shaded PV

Unshaded PV

35-40°

SE – SW

Shade

W

S

E

70 6550

65

1 0 0 9 59 0

9 5

% of maximum output

Figure 1 Shading, inclination and orientation impact PV array efficiency

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3A place in the sun

Mounting

A number of modules connected together are

referred to as an array. PV modules can be

designed into the building envelope, forexample, replacing walling, cladding or roofing

components, or can be mounted separately on

purpose-built frames. Thin film solar cell can be

applied to materials such as glass or metal.

Generation

PVs work well for buildings where electricity

is needed year-round in daylight hours, as

electricity generated can contribute to abuilding’s daytime demands. If more electricity

is generated than the building needs, this energy

can be exported to the National Grid.

Frame-mounted PVs on the roof of Stoke Local Services Centre (left), and building integrated PV into rooflight glazing at theLondon School of Hygiene and Tropical Medicine

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4A place in the sun

Why choose PVs?

I you have enough space or installation, access to sunlight, and no risk o overshadowingrom nearby buildings or trees, PVs may be a viable choice or your project.

Motivations

When we asked our project teams why they

chose PVs, we received a variety of responses:

•Once installed, PVs are silent and easy to run.

•Highly visible panels can make a bold

sustainability statement.

•Equally, panels can be integrated or hidden

where appearances matter.

•They are a tried and tested technology

with low maintenance costs.

Funding and payback period

None of the case study projects qualified for

the feed-in tariff as they received grant funding.

If The City Academy, Hackney, for example, had

been eligible to receive the feed-in tariff, it

would have received £3,690 a year, based on

a generation tariff of 31.4p/kWh and an export

tariff of 3p/kWh. This income is in addition

to an estimated £1,050 in electricity savings.

The payback period for The City Academy is

approximately 29 years. The payback for Stoke

Local Services Centre is 16.5 years. The payback

periods for the case study projects would be

shorter if current capital costs are used and if

the panels were all achieving their theoretical

performance (i.e. were not overshadowed and

were facing directly south):

•The capital costs for four of the case

study projects were between £6,200

and £6,500/kWp (a measure of system

size). Current capital costs are less

than £4,500/kWp.

•The performance of the panels at Hackney

is 552kWh/kWp when it could, theoretically,

achieve 850kWh/kWp. Stoke is achievinga good performance.

Taking into account these two factors would

reduce the payback periods to 23 years for

The City Academy and 12 years for Stoke.

Feed-in tariff

The feed-in tariff (or clean energy

cashback) provides an additional

incentive to install PV. If you opt in youwill be paid for generating electricity

from PV and receive further income for

exporting electricity to the National Grid.

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5A place in the sun

London School of Hygiene & Tropical Medicine’s SouthCourtyard Development view of the atrium looking upto the BIPV roof

Costs

Installed costs ranged between £6,200 and

£6,500kWp for standard ‘bolt-on’ types of panel.

The costs increased quickly on projects where:

•access was difficult

•PV was integrated into other building elements

•PV was used for aesthetic enhancement.

Live energy information

The City Academy engaged and

educated pupils, teachers and visitors

by installing a display panel in the schooldemonstrating the cumulative CO2 savings

from the PVs and other low and zero carbon

(LZC) energy sources on the site, with ‘live’

information about energy consumption.

Carbon reduction

The projects we looked at found their

PV installations contributed to reductions

in CO2 of up to 10% compared to 2006

building regulations.

Several sites were motivated by the fact that

PVs are easy to monitor and can provide ‘real

time’ data on their effectiveness.

Provided PVs were installed correctly and

overshadowing was avoided, they were found

to perform as expected or better.

The installations at One Brighton and Dandridges

Mill were tested and proven to generate levels

of electricity as good as, if not better, than those

predicted at design stage.

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6A place in the sun

Made to fit

In one project planning constraints meant

PV panels had to be integrated within

the rooflight system. This was more expensivethan predicted as the design was bespoke,

so a number of non-standard panels had to

be manufactured. This increased the capital

cost to £33,500/kWp.

The City Academy’s original renewable energy

strategy included a solar thermal system, but

this had to be rethought during the tender stage

due to escalating costs. They therefore

considered PV and found it was significantlymore cost-effective in terms of money spent per

kgCO2 saved than solar thermal and ground

source heat pumps (see Figure 2 ).

The total installed capital

costs of PV per kg of CO2

saved can be lower than

other renewable energy

technologies.

Lessons learned

• The PVs performed well when correctly

installed and when they weren’t

overshadowed.

• They are silent and easy to run

and maintain.

• Surplus generation can be sold back

to the Grid and financial incentives

are in place.

• When comparing CO2 reductions

against money invested, PVs can

compare favourably to solar hot water

and ground source heat pumps.

• PVs can be used to make a statement,

can be integrated into the building,

or hidden from view depending on

the demands of the project.

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7A place in the sun

Assessing site feasibilityThe success o PVs depends on the suitability o the site. It is important to

consider overshadowing, mounting and the visual impact o the installation.

Predicting output

It is easy to quickly estimate output from

a solar array, once you’ve assessed the potential

location, using the manufacturer’s data on

system efficiency and the solar data as shown

on Figure 2 .

Figure 3 shows a comparison of the predicted

and the monitored energy output from the PV

panels for the case study projects. Three case

studies overestimated the energy output and

two underestimated the use. The overestimates

are caused by a combination of the assumptions

and modelling tools used to predict energyoutput, and some underperformance due

to overshading.

Figure 2 Map showing available solar energy

across the UK

750

800

850

900

950

1000

1050

1100

kWh/m2 /year

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8A place in the sun

Avoiding overshading

Consultants and specialists are able to make

fairly robust predictions about the performance

of PV for most building types and locations.

However, it’s essential that you consider the

effects of overshadowing from trees and

neighbouring buildings. Even a small amount

can dramatically reduce the electrical output

of a PV array.

At Fairglen some housing units could not be

fitted with PV panels because they were in

the shade of existing trees.

At Stoke Local Service Centre the final panel

positions were determined by solar shading

analysis, taking into account surrounding

buildings and the Clock Tower.0%

1,500

3,000

4,500

6,000

7,500

9,000

10,500

12,000

13,500

15,000

E n e r g y o u t p u t ( k W h / y e a r )

Predicted energy output (kWh/yr)

Monitored energy output (kWh/yr)

Hackney

Academy,

London

Fair Glen,

Phase 1

(two houses)

One BrightonLondon School

of Hygiene and

Tropical Medicine

Stoke Local

Services Centre,

Stoke-on-Trent

5,400

10,122

1,915 2,101

15,000

11,641

5,750

2,500

7,930

6,936

Figure 3 A comparison of the predicted and the monitored energy output from

the PV panels for the case study projects

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9A place in the sun

PV panels at Stoke Local Service Centre are on framesto achieve optimum inclination and solar access. The panelsare hidden from view.

Mounting

PVs are a very flexible option. They can

be incorporated into buildings using:

• roof-based systems

• façade systems

•shading devices.

When PVs are added to an existing building

where the orientation and solar access are

already fixed, they can sometimes be mounted

on special frames to make sure they receive

maximum sunlight. The cost of framing and

integrating the panels onto the roof for Stoke

Local Service Centre was approximately

26% of the total capital cost (£52,000).

Dandridges Mill, The City Academy and Stoke

Local Service Centre used purpose-built roof

frames to ensure their PVs were south facing

and 30° to 35° from the horizontal plane.

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10A place in the sun

Roof-mounted PV panels at Dandridge’s Mill(a Grade II listed building)

Visual impact

If you’re considering PVs you’ll need to decide

whether you need to minimise the visual impact

to satisfy planning constraints – for example,in conservation areas or on listed buildings –

or to enhance it to promote the sustainable

nature of the building.

For Stoke Local Service Centre, planning

permission was straightforward because the

local authority endorsed the project’s low

carbon aspirations.

Dandridge’s Mill, a Grade II listed building, won

approval for panels after they were shown to be

an integral part of the low carbon strategy.

The South Courtyard Development at LSHTM

is surrounded on all four sides by Grade II listed

buildings, leaving the roof as the only viable

place for an array. For aesthetic reasons, the

planning authorities insisted on a Building

Integrated Photovoltaics (BIV) solution, but the

client raised concerns that this would block the

view from the building and prevent daylight from

coming in. Although it diminished the electrical

output, the designers reduced the density of the

PV cells within the laminated roof glazing,

retaining the daylight and views and overall

aesthetic appeal of the designed space.

Lessons learned

• It is quick and easy to predict the

output of a PV installation.

• It’s important to assess solar access

through solar modelling and/or site

investigations.

• A small amount of overshading

can dramatically reduce performance

if you don’t compensate for it in the

design of the array.

• PVs are flexible, with multiple

installation options.

• Frame mounting can allow elevation

or rotation for optimum exposure.

• Visible PVs are becoming increasingly

acceptable – even desirable.

• Speaking to planners early allows you

to resolve any aesthetic conflicts.

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Procurement and installationFinding experienced delivery partners, ostering good relationships and

setting up collaborative work practices are all essential to project success.

Building successful teams

To achieve a successful project it’s essential that

your engineers and contractors have experience

in designing and installing PVs.

At The City Academy the design team remained

mostly the same throughout the project, and the

expertise of the consulting engineers added

considerably to the success.

The way that contracts are managed can

also make a difference.

Contracts

At Stoke Local Service Centre the fact that the

contractor was appointed via the framework

agreement meant that he was able to provide

valuable input early in the design to manage risk

and improve the efficiency of the programme.

All work packages, including renewable energy

systems, were competitively tendered through

the main contractor.

The City Academy used a Project Partnering

Agreement (PPC2000) to foster mutual trust

and co-operation through the design, supply

and construction processes.

Coordination

Briefing contractors about the overall design

of the building enables them to take other

aspects of the design into consideration.

One project suffered from a lack ofco-ordination during the early design stages

and it later transpired that roof-mounted

ductwork overshadowed the PV array. This

reduced the amount of electricity produced.

The PV array is overshadowed by ductwork and access stairs

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Controlling costs

Early involvement of an experienced contractor,

quantity surveyor and engineer will help to give

better predictions of capital costs.

The tender process needs to balance experience

and knowledge with cost.

At One New Brighton, planning constraints

meant arrays could only be mounted on one

building. Fortunately, the design team was able

to source higher performing panels and generate

sufficient electricity from one rooftop array.

The higher performing panels cost more, but

a lower specification would have compromised

the entire scheme.

One New Brighton PV array with simple frame

Modules and equipment

Controls and equipment

Installation

Builder’s work

Commissioning

11%

8%

22%

50%

9%

Figure 4 Cost breakdown for PV installation

at Stoke Local Service Centre

Engage contractors early

and allow them to inform

the design

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Disparity between tender costs and final

costs is often down to overlooked ancillary

items from specialist equipment, installation

and commissioning costs to meeting planning

requirements and developing bespoke

design solutions.

At Stoke Local Service Centre the additional cost

of controls and equipment, installation, builder’s

work and commissioning were roughly equal

to the cost of the PV modules themselves.

On another project, the bespoke nature of the

integrated system demanded by planning meant

that final costs were as much as five timesthose predicted at earlier stages.

Lessons learned

• Organise tendering processes to score

on experience and commitment as well

as cost.

• Choose contractors and suppliers with

experience of similar scale installations.

• Ensure all suppliers and contractors

are briefed on the design intent and

bigger vision.

• Bespoke solutions and ancillary items

can cause costs to spiral.

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Ensuring best performancePeople oten overlook the need or commissioning, monitoring and engaging the Facilities

Management team. All three are vital to ensuring the building works as intended.

Metering

The projects demonstrate that successful

commissioning, monitoring and running of any

PV system is assisted by a good submetering

strategy – that is, a meter to monitor the

electrical output from every array.

Fairglen used submetering to assess the

performance of the renewable technologies

in a domestic setting so they could identify

technology choices for future sustainable

housing developments.

At One Brighton, the Green Caretaker has

to manually read the PV meters each monthand divide the savings between dwellings.

This could have been managed by an

automatic submeter.

Figure 5 A typical daily report showing building integrated PV output over a peak day

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Commissioning

Commissioning the PVs at the case study

projects was generally very quick and easy

and took less than a day. Generally, ongoingcommissioning is not necessary for PVs.

While commissioning PV systems is

relatively simple, it was found to be

worthwhile to keep specialists involved

through the commissioning stage.

Proper commissioning helps ensure the PV’s

electrical systems are safe. On one project, the

commissioning engineer suggested installing

railings on the roof to ensure inspections could

be safely carried out.

At The City Academy, commissioning was

shared by the electricity distributer and the

specialist PV installer to make sure both parties

were happy with safety measures.

Handover and monitoring

A PV system and the metering and monitoring

system may require fine-tuning to ensure

readings are calibrated properly.

Monitoring allows you to check that the PVs are

generating to predicted levels, and helps identify

shortfalls or faults.

Monitoring was an important consideration at

Stoke Local Service Centre. Local inverters

display the energy generated from each panel

and overall consumption data is converted and

logged onto the BMS.

Early collaboration between

the designers, PV suppliers

and commissioning specialists

will ensure an integrated

approach towards successfulinstallation and operation

of the PV system

Maintenance

One of the appealing aspects of a PV system

is that maintenance requirements are low.

However, the facilities management still needto clean the panels periodically, monitor

performance and check the electrical installations.

The performance needs to be monitored to

ensure that the panels and inverters are still

functioning. Inverters have a typical warranty

period of between five and 10 years, with some

covered for 15 years, but there were some early

failures documented in case study projects.

As a rough guide, inverters cost between

5% and 10% of the system cost. Some of

the case study projects have set up a fund

to cover replacement costs as part of the

maintenance budget.

The panels’ performance degrades by 0.5%

per annum. The PV modules are typically

covered by a 25-year limited warranty of 80%

power output or a 12-year limited warranty

of 90% power output.

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Constant supply

The electricity supply from PV modules cannot

be switched off, so you’ll need to take special

precautions to make sure that live parts are notaccessible during routine maintenance.

At The City Academy the building’s facilities

manager has allowed £500 per annum to

carry out the following maintenance:

•modules cleaned every six months

•output monitored

•periodic electrical inspections.

This accords with the rule of thumb that

assumes £20/kWp per year which includes

a fund to replace the inverters every five to

10 years.

At Fairglen low energy housing project the

residents are responsible for maintenance.

The customer manual recommends that PV

panels are cleaned every six months, and a full

electrical inspection carried out every 10 years.

Inverters installed under PV panels

Lessons learned

• Factor in adequate metering from the

outset to maintain performance and

to claim the feed-in tariff.

• Commissioning is quick, but some

post-commissioning monitoring is

necessary. The output should be

checked at least once a month.

• Consider who is responsible for

ongoing cleaning and maintenance.

• Make sure facilities management is

trained on how the system should

operate and perform.

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17Photovoltaics

Hackney Academy,

London

London School

of Hygiene and

Tropical Medicine

Stoke Local

Service Centre,

Stoke-on-Trent

Fair Glen, Phase 1

(two houses)

One Brighton

Description of

project

New build

school academy

Refurbishment of

Grade II listed

university building

New build extension

to community

building,

New build

residential houses

New build

residential

apartments

Rating of PV array 21.1 7.4 8.3 2.4 9.36

Area of PV array

(m2)

175 57 59.4 55 68

Predicted energy

output kWh/yr

15,000 5,750 7,930 1,915 5,400

Monitored energy

output kWh/yr

11,641 2,500 6,936 2,101 10,122

Monitored kWh/

kWp

552 338 836 875 1,081

Cost per kW £6,445 £33,496 £6,265 £6,940 £6,944

Total cost (supply,

installation, testing

and commissioning)

£136,000 £247,867 £52,000 £16,655 £65,000

Project summaries

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CIBSEUnderstanding Building Photovoltaics,

2000.

Intended to provide guidance for engineersand other building professionals

on the design of PV in buildings.

Capturing Solar Energy, 2009.

An overview of the available solar system

solutions, technologies and applications for

buildings. It considers design and installation

issues as well as commissioning andmaintenance requirements.

Carbon Trust Feed-in Tariffs Policy and Markets Guide.

Information for organisations interested

in applying for feed-in tariffs

Department of Tradeand Industry

Photovoltaics in buildings. Guide to the

installation of PV systems. 2nd edition,

2006.

Intended to assist supply system installers

to ensure that mains-connected

PV systems meet UK standards and best

practice recommendations.

Further information

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http://www.cibse.org/index.cfm?go=publications.view&item=46





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CTG038

The Carbon Trust receives funding from Government including the Department of Energy and Climate Change, the Department

for Transport, the Scottish Government, the Welsh Assembly Government and Invest Northern Ireland.

Whilst reasonable steps have been taken to ensure that the information contained within this publication is correct, the authors,

the Carbon Trust, its agents, contractors and sub-contractors give no warranty and make no representation as to its accuracy

and accept no liability for any errors or omissions. Any trademarks, service marks or logos used in this publication, and copyright

in it, are the property of the Carbon Trust. Nothing in this publication shall be construed as granting any licence or right to useor reproduce any of the trademarks, service marks, logos, copyright or any proprietary information n any way without the

Carbon Trust’s prior written permission. The Carbon Trust enforces infringements of its intellectual property rights to the full

extent permitted by law.

The Carbon Trust is a company limited by guarantee and registered in England and Wales under Company number 4190230

with its Registered Office at: 6th Floor, 5 New Street Square, London EC4A 3BF.

Published in the UK: March 2011.

© Queen’s Printer and Controller of HMSO..

The Carbon Trust is a not-for-profit company with the mission to accelerate the move to a low carbon economy.

We provide specialist support to business and the public sector to help cut carbon emissions, save energy and

commercialise low carbon technologies. By stimulating low carbon action we contribute to key UK goals of lower

carbon emissions, the development of low carbon businesses, increased energy security and associated jobs.

We help to cut carbon emissions now by:

• providing specialist advice and finance to help organisations cut carbon

• setting standards for carbon reduction.

We reduce potential future carbon emissions by:

• opening markets for low carbon technologies

• leading industry collaborations to commercialise technologies

• investing in early-stage low carbon companies.

www.carbontrust.co.uk

0800 085 2005

2011 ctg038 a place in the sun photovoltaic electricity generation

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