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7/27/2019 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
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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
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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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11A place in the sun
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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12A place in the sun
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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13A place in the sun
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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14A place in the sun
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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15A place in the sun
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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16A place in the sun
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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18A place in the sun
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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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
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