and agree a schedule for the proper method of repair to the roof above Mr Anderson’s property
Draft Solar PV Panel Report Date: - 30th January 2015
Prepared by: - Alan Williamson BSc(Hons), CEng, M.I.C.E, M.I.Struct.E, F.I.O.R.
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SPECTRUM CENTRE – GUILDFORD
DRAFT FEASIBILITY REPORT ON SOLAR PV PANELS
Page 2 of 24 30.01.2015
This report has been prepared for the sole benefit, use and information of Guildford Borough
Council and the liability of A P Williamson Consultants Ltd, in respect of the information
contained in the report will not extend to any third party.
CONTENTS
Page 3 of 24 30.01.2015
1. Instruction / Introduction................................................
2. Statement of Truth........................................................
3. Qualifications of writer...................................................
4. Information Sources.....................................................
5. Executive Summary......................................................
6. Discussion on solar photovoltaic installations………….
7. Feasibility of installation of a solar PV system…………
7.1 Solar PV system on roof………………………………….
7.2 Roof glazing with solar PV………………………………..
7.3 Curtain wall glazing with solar PV………………………..
8. Conclusions / Recommendations………………………..
Appendix A – Roof Plans and elevations
Appendix B – Roof plan of proposed solar PV application
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1. INTRODUCTION/ INSTRUCTION
1.1 The building achieved practical completion on 19 January 1993, and as a result
of various defects associated with the building it has been recommended by
APWCL, in a feasibility report dated March 2014 (as instructed by Guildford
Borough Council (GBC)), to re-roof the building as well as carry out other
associated works to address these other defects (e.g. improve the air handling
to the swimming pool areas).
1.2 In 2008 repair works were undertaken to the roofs to provide adequate safe roof
access and since then a solar panel array has been erected on a part of the
roof on the south elevation, west end as can be seen in the cover photograph
on the cover page, and also marked on a plan in Appendix B.
1.3 Subsequent to that report instructions have been received from Guildford
Borough Council to report on the feasibility of introducing solar photovoltaics on
the roof and roof glazing, as a part of the re-roofing scheme.
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2. STATEMENT OF TRUTH
I confirm that in so far as the facts stated in my report are within my own
knowledge I have made clear which they are and I believe them to be true, and
that opinions I have expressed represent my true and complete professional
opinion.
Signed:
A P Williamson
Date: 30.01.2015
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3. QUALIFICATIONS OF WRITERU
3.1 The writer of this report, Mr. A. P. Williamson B.Sc. (Hons), C.Eng. M.I.C.E.,
M.I.Struct.E., F.I.O.R. has been employed in the Construction Industry for the
last 47 years.
3.2 The work experience has varied from working for Civil Engineering Contractors
on various projects such as motorways and airports, working for a Local
Authority on Highway designs, working for a firm of Consultant Engineers on
various Structural designs, working for a Transport Authority on the design and
installation of various railway structures and maintenance of properties, and for
the last 28 years being involved specifically in the Roofing and Cladding
Industry.
3.3 Experience in the Roofing and Cladding Industry was with a Roofing and
Cladding Contractor for a period of 16 years, involved in Design and Build
contracting for many varied Clients such as Railway Authorities, Housing
Authorities, Banks, Main Contractors, Developers, School Authorities, Health
Authorities and many others.
3.4 Experience of roofing and cladding works has been gained in the design and
installation of Industrial Roofing and cladding, from renovation to new build,
using many varied systems ranging from self supporting pierce fixed
constructions to standing seam constructions, and various materials have been
used such as asbestos cement and fibre cement roof sheets, plastisol coated
steel, stainless steel and colour coated aluminium.
3.5 The roofing works have incorporated other elements such as various types of
glazing systems, including patent glazing and glazed curtain walling systems
and also various forms of roof drainage, ventilation systems, roof access and
safety systems and associated elements such as secondary steel supports.
Experience was also gained in other systems such as built – up felt, single ply
membranes, slating and tiling, and also the decking supports to many of these
coverings.
3.6 Experience of cladding works involved the design and installation of, for
example, twin skin metal constructions, with both over and under rail lining,
Page 7 of 24 30.01.2015
composite panels laid both vertically and horizontally, twin skin construction
using a variety of different board materials, curtain walling and various types of
glazing systems, acoustic sound attenuation louver screens, and other similar
constructions including insulated render systems.
3.7 These cladding works have also included integrated window systems and also
curtain walling.
3.8 I have also had experience in fully supported standing seam stainless steel
roofing, and have aided in the design of various elements of its construction,
such as eaves and verge details.
3.9 These works have been carried out on both new build and renovation projects
using various forms of contract in many different environments such as green
field sites and occupied premises and the value of the largest roofing and
cladding contract undertaken was £5m, which included over-roofing using a
standing seam pitched roof with cold rolled galvanised steel section truss
support over a flat roof to a Railway Depot.
3.10 I was a member of the B.S.I representing the National Federation of Roofing
Contractors on various Technical Code Drafting committees such as the
revision to BS 5247, and various CEN committees, and was a committee
member of the London and Southern Counties region of the N.F.R.C. and sat
on the drafting committee of the 3rd Edition of the Guide to Good Practise being
specifically responsible for the roof drainage section, and was the chairman of
the N.F.R.C. Technical Sheeting and Cladding Committee, and represented the
N.F.R.C. on a number of training committees with the C.I.T.B. involving N.V.Q.
qualifications and also safety related matters.
3.11 I was also a Technical Committee member of the ZELRO (zero leaks in roofing)
group established by leading developers and clients in conjunction with the then
Building Research Establishment to produce a good practise code to be used
with projects that were associated with the client group.
3.12 I was also a Board member of the Institute of Roofing and have act as a judge
at the National Federation of Roofing Contractors Roofing awards.
Page 8 of 24 30.01.2015
3.13 Apart from carrying out forensic inspections for many varied clients, as a
Consultant, I also carry out designs for gutters, secondary steelwork, various
cladding elements and curtain walling, and have acted as a Consultant for a
major manufacturer of roofing products.
3.14 I have also acted as an Expert Witness in cases involving disputes associated
with many of the above-mentioned disciplines.
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4. INFORMATION SCOURCESU
4.1. Information provided by GBC regarding current system operated with regards to
pay back of electricity generated using solar panels.
4.2. Information of Polysolar PV Glazing units (transparent and opaque amorphous
– silicon - thin - film glass laminate photovoltaic BIPV glazing unit).
4.3. Kalzip solar solutions.
4.4. SolarPv.co.uk. – Solar film
4.5. A-Sun – Innovative solar products.
4.6. Pilkington Solar Energy
4.7. International Renewable Energy Agency (IRENA) – Renewable Energy
Technologies: Cost Analysis series – Volume 1: Power sector issue 4/5 – Solar
Photovoltaic’s.
4.8. BRE Digest DG 489 – Wind loads on roof- mounted photovoltaic and solar
thermal systems.
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5. EXECUTIVE SUMMARY
5.1. I am of the opinion that the existing solar PV panels on the existing roof (i.e.
over the competition pools on the south side of the building towards the west)
should be maintained when re-roofing is carried out in the near future.
5.2. It would also be of benefit to introduce a similar area of solar PV panels over the
leisure pools on the south side of the building towards the east.
5.3. However, depending upon the system offered by a Contractor (as there are
various types), this installation would be subject to structural analysis of the new
roof cladding (and structure), as required by the Building Regulations, to
accommodate the new added loading of the system.
5.4. If this analysis shows that strengthening works were required (to accommodate
not only this dead load, and possibly the wind load effects) these costs have not
been included in the budget costings in section 8 of this report.
5.5. The use of solar PV panels on the other areas of the roof (i.e. particularly on
north facing slopes) by the nature of the way these panels works, they would
not be efficient and are not recommended.
5.6. Solar PV glazing could be introduced into the south glazed slopes of the
‘Street’, where it would be most efficient but its introduction elsewhere, because
of the shape of the roofs and glazing would have an adverse effect with regards
to shading and also orientation, all of which effects the efficiency of the system’s
electrical production and is not cost effective.
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6. DISCUSSION ON SOLAR PHOTOVOLTAIC INSTALLATIONS
6.1. For a number of years, the production of electricity using renewable methods has
becoming increasingly important and the conversion of solar energy into
electricity using photovoltaics is one solution that is particularly applicable to
roofing and glazing.
6.2. There are, basically, two different types of systems, with a number of sub-
divisions of type within these.
6.3. They work on the basis that they capture the sun’s energy using photovoltaic
cells. These cells convert the sunlight into direct current electricity, via a physical
reaction and because they do not need direct sunlight can do so even on a
cloudy day. These cells are normally connected in series to form photovoltaic
cells.
6.4. The direct current electricity is converted to alternating current, which is what
powers most electrical appliances and is how the grid is transmitted, and this is
achieved by using an inverter.
6.5. One type of system (which is the older and more established technology) is a first
generation PV system that uses wafer – based crystalline silicon (c – Si)
technology. This then takes the form of either single crystalline (sc-Si) or multi-
crystalline (mc-Si) technology.
6.6. This system takes the form of panel modules supported of off the roof structure,
which is the most common solar photovoltaic system used.
6.7. However, given the type of support, i.e. installed above the roof surface, checks
should be carried out in accordance with BRE Digest 489 to ensure that they and
the roof are able to safely carry the wind loads.
6.8. It is also necessary to check any additional loads imposed on the roof from the
self-weight of the modules and support system, wind-induced effects, weight of
snow and any loads imposed during construction. If a retrofit solar system
increases the applied roof loading by more than 15% then Approved Document A
of the Building Regulations requires that the structural integrity of the roof
structure and supporting structure be carried out.
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6.9. Given that the weight of solar panels are approximately 13Kg/m2 and the dead
weight of a twin skin aluminium roof is in the order of 12kg/m2, then, in all
probability, it would be necessary to carry out this check.
6.10. A typical type of 1st generation solar PV panel module attached to a trapezoidal
profile roof sheet is shown in image 1 below.
Image 1 1st generation solar PV module attached to a trapezoidal profile roof sheet
6.11. The other type of system (which is more modern, but less well established) is a
2nd generation system that uses thin films solar cells, which are composed of
successive thin layers (1 to 4μ thick) of solar cells sandwiched between large
inexpensive substrates such metal, glass or polymer.
6.12. As a consequence of this form of manufacture they require considerably less
semi-conductor material than crystalline solar cells to absorb the same amount of
sunlight.
6.13. There are a number of thin film photovoltaic technologies that have been
developed and these include amorphous silicon (a – Si), Cadmium Telluride (Cd
– Te) and Copper – Indium – Selenide (CIS) and Copper – Indium – Diselenide
(CIGS).
6.14. Amorphous silicon solar cells are the most developed and used thin-film solar
cells and are bonded to substrates such as glass and aluminium.
6.15. When bonded to aluminium they form a lightweight panel, which can be used as
an in-plane system mounted either longitudinally, or transversely to say
aluminium profiled roof sheets, see image 2.
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Image 2 2nd generation solar PV panel modules attached to an aluminium standing seam roof
6.16. When bonded to aluminium the thin-film solar panels weigh approximately half
that of wafer based crystalline solar cells, i.e. approximately 6Kg/m2 however they
will probably be more than 15% of the existing applied roof load and so checks
on the roof and its supporting structure may be needed.
6.17. There is yet another technical development of thin-film solar technology, whereby
the thin-film laminates are deposited onto a stainless steel foil and encapsulated
in an ethane vinyl acetate (EVA) co-polymer protective envelope. These are triple
– junction manufacture and each of the three cells converts a different part of the
visible spectrum, which has the result of efficient conversion in overcast
conditions.
6.18. These PV laminates are then factory-bonded to polyester or PVDF paint coated
aluminium standing seam roof sheets, such that they form a homogenous fully
integrated system, which includes an inverter and accessories. These roof sheets
are then used in a twin skin insulated roofing system, forming the top-weathering
sheet. See image 3.
Image 3 Integrally bonded solar PV roof sheeting
Page 14 of 24 30.01.2015
6.19. Currently, only one manufacturer, with only one type of standing seam profile,
markets this technology in the UK. The additional weight of the PV laminate is
only in the order of some 2.7Kg/m2 but a structural check would also probably be
required.
6.20. With this factory bonded system of roof panels there are two different types,
which produce different power outputs and these depend upon length.
6.21. PV solar technology is also available for glazing and the Spectrum Centre
contains roof glazing in the form of vertical glazing with pitched glazing above.
These areas run from east to west dividing off the pool areas from the ice rink
and arenas, the ‘Street’, and also from north to south forming dividing areas
between the competition and leisure pools and also between the arena and ice
rinks.
6.22. There are also areas of glazed curtain walling in the façade of the building where
PV solar technology could be used.
6.23. There are various types of PV solar technology available for glazing use and
these are as follows: -
Transparent Solar PV glass – Crystalline solar PV panels are opaque and
the background material is glass, and it is this that is transparent.
Semi-transparent solar PV glass – By adjusting the distance between the
solar PV cells it is possible to regulate the light transmission and when he
solar PV cells are positioned more closely together they become semi-
transparent and produce a dappled effect.
Solar PV thin film on glass – where thin film cells are printed on glass in
several thin layers.
6.24. The solar PV thin film technology, which consists of, in section, front glass, a
TCO (transparent conductive oxide) layer, PV thin film absorbing layers, a back
contact (white reflector), an encapsulant (lamination foil) and a back glass, is
transparent.
Page 15 of 24 30.01.2015
6.25. It is possible to have an additional white reflector that makes the unit more
opaque but this reflects light back into the unit to generate approximately 10%
more power.
6.26. Typical examples of different types of solar PV glazing are shown in Image 4
below:
Image 4 Solar PV glass Semi-transparent Solar PV glass Solar PV thin film glass
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7. FEASIBILITY OF INSTALLATION OF A SOLAR PV SYSTEM
7.1 SOLAR PV SYTEM ON ROOF
7.1.1. There are, basically two types of solar PV systems that can be used on the roofs.
One type is that of using solar panels (as is currently used on the roofs), the other
type is to use thin-film solar technology on roof panels.
7.1.2. However there are differences between the two systems with regards to their
costs, efficiency and energy generation.
7.1.3. The 1st generation systems (using wafer – based crystalline silicon (c – Si)
technology) is more efficient (≈ 15%) than compared to thin film technology (≈
10%), albeit it costs more to manufacture 1st generation technology solar PV
modules than 2nd generation ≈ 1.4$/W (0.93£/W) compared to 0.8$/W (0.53£/W).
7.1.4. The area needed to generate 1KW of electricity for a 1st generation system is
approximately 7m2 and that of a 2nd generation system is 15m2. So a 2nd
generation system will require approximately 2.14 times more area to produce
the same amount of electricity as a 1st generation system.
7.1.5. This means that it would require 2.14 times more 2nd generation modules to
generate the same amount of electricity as a 1st generation module, at a cost
ratio of 2.14 x 0.8 to 1.4 = 1.71 to 1.4 ≈ 22% more cost.
7.1.6. However when using thin film solar PV bonded onto aluminium standing seam
roof sheets something in the order of 18.5m2 is required to produce 1KW and so
this would require approximately 2.64 times more area to produce the same
amount of electricity as a 1st generation system.
7.1.7. However the cost noted in 7.1.5 above does not represent a true total cost, as the
total cost of a solar PV system comprises of two basic components, i.e. the PV
module cost and the Balance of System (BOS) cost.
7.1.8. The BOS cost includes items such as structural support, installation, and
electrical system costs etc.
7.1.9. All of these costs can vary widely depending upon the site location etc, but as a
rough guide the module cost is some 50% of a total cost, but in the case of 2nd
generation technology, where the roof panel contains solar PV technology, the
Page 17 of 24 30.01.2015
installation costs are reduced as the installation costs of the PV is contained
within the cost of installing the roof sheet.
7.1.10. However, when using roof sheets that contain solar PV technology, although the
cost of the roof sheet is increased there is no need for the costs of panel support
and any other possible structural costs.
7.1.11. Also, with either type of system there are limitations as to the use of solar PV
technology and one of the main limitations is that of the orientation of the system
to adequately collect solar power.
7.1.12. The optimum position is facing due south at an angle of some 30° from the
horizontal. However the majority of the roofs at the Spectrum Centre are at
approximately 11° from the horizontal and if laid at the optimum angle would
require not only additional support work to accommodate this but in turn the
supports would need to be even stronger as the solar panels would act as free
standing canopies (as per BRE Digest DG489) which would mean greater wind
uplift loads.
7.1.13. The building is virtually orientated such that the elevation facing Parkway Road is
facing south and from the south side of the ‘Street’ (which runs virtually east –
west) the roof slopes towards the south, whereas on the north side of the ‘Street’
the roofs slope towards north, so if solar PV panels were installed parallel to the
existing roof surface (south facing) then this would mean an efficiency of
approximately 97% when compared to 100% for 30° inclination facing south.
7.1.14. A plan and elevations of the building are shown in Appendix A.
7.1.15. It is possible to orientate solar panels to face the west or the east but at 11°
inclination these would only be some 84% as efficient as at 30° inclination facing
due south. So it is more efficient so site any solar PV system such that it is
located on the south side of the ‘Street’.
7.1.16. Shading also has an adverse effect on the output of solar PV panels. When
partially or temporarily shaded, amorphous thin-film laminates (2nd generation)
have at their disposal a bypass circuit, so that the total system power is not
significantly reduced, approximately 10% loss.
Page 18 of 24 30.01.2015
7.1.17. This is not the case with similarly – shaded crystalline panels (1st generation)
which in the event of partial shading loses a significantly greater output,
approximately 50% loss.
7.1.18. It is a fact that the west side of the site is bordered by reasonably mature trees
and that is probably why the existing solar PV roof panels do not extend over to
the west.
7.1.19. Yet another factor that effects the output of both 1st and 2nd generation solar PV
panels is that of the cell temperature and a higher cell temperature produces a
greater loss in 1st generation when compared to 2nd generation and as the
temperature increases so does the loss (by as much as approximately 20% for
an 80°C cell temperature (there is no loss at 25°C).
7.2 ROOF GLAZING WITH SOLAR PV
7.2.1. As with the roof solar PV orientation, all south facing glass will receive more
sunlight and be more efficient than any other direction.
7.2.2. However there is vertical glass, which of solar PV glazing were used on the south
elevation will be approximately 65% efficient compared to the south facing
sloping roof 30° inclination (100%) and there is also roof glass which varies from
approximately 13° to 27°, depending upon which way it faces.
7.2.3. For west or east facing glass at 27° inclination from the horizontal the efficiency is
approximately 78% that of the optimum and for south facing roof glass at 11°
inclination from the vertical the efficiency is some 97% of the optimum.
7.2.4. There is considerable shading to the vertical glazing on this roof on the east face
of the west of the North-South glazing runs over the Leisure Pool and also to the
west face of the east of the North-South glazing runs over the Leisure Pool, as
they form an almost enclosed area.
7.2.5. Similarly there is shading to the west and east faces of these vertical glazing runs
albeit not to such an extent.
7.2.6. The optimum location for solar PV glazing is on the sloping roof glazing to the
south side of the ‘Street’, where it will work at maximum efficiency.
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7.2.7. This type of glazing also reduces solar gain, which however given the proposed
location of the installation would not provide much of a benefit.
7.3 CURTAIN WALLING GLAZING WITH SOLAR PV
7.3.1. The curtain walling to the south elevation of the competition pool and to the area
between the competition and Leisure pools would be the optimum locations for
solar PV glazing, however as this glass is vertical, it is only 65% efficient, when
compared to solar PV glazing at an angle of inclination of 30° to the horizontal.
7.4 On east and west facing elevations (regardless of shading) the efficiency of
vertical solar PV glazing is only 50%.
7.5 Now, although the 2nd generation solar PV technologies that are used in glazing
are more tolerant of shading than 1st generation technologies, shading still
reduces output.
7.6 So vertical solar PV glazing, is inefficient when compared to roof solar PV glazing
8. CONCLUSION/RECOMMENDATION
8.1. There is an existing solar PV system on the south slopes of the roof over the
competition pool, which will be removed and re-fixed in conjunction with the new
roofing works.
8.2. This system (according to data supplied by GBC) currently provides some
27000KWh per annum and covers an area of approximately 190m2. This system
was only recently installed and so the retention would still provide a benefit. The
cost of removing and replacing this system has been accounted for in the March
2014 report on re-roofing.
8.3. 2nd generation solar PV coated aluminium roof sheets, are less efficient than
solar PV panels, albeit they are cheaper. However, currently, there is only one
manufacturer and so in order to ensure continuity and integrity of the roof
sheeting, if this system were to be used, the entire area (where solar PV is to be
introduced) would have to be roofed in the same material, albeit without the solar
coating.
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8.4. The optimum area of roof for solar PV is that of the areas over the pools, i.e. the
south side of the building and a reasonable area of this is shaded during various
times of the day, which would reduce electricity production.
8.5. The use of this type of roof sheeting (i.e. solar PV integral coated) would restrict
competition with regards to the manufacturer and its use is limited.
8.6. The introduction of solar PV panels, similar to the existing, on the east side of the
roof over the leisure pool would however generate similar amounts of electricity,
approximately 20000KWh at an approximate installation cost of £40000 and it is
estimated that payback would be achieved after a period of some 13 years.
8.7. This is based on the assumption that after a structural analysis of the existing
roof and structure, to accommodate the likely increased loadings, that no
structural works are required.
8.8. The introduction of solar PV glazing to the south slopes of the ‘Street, whilst re-
roofing and re-glazing were being carried out would basically only attract an extra
over cost of the solar PV to the outer of the insulated glazing units.
8.9. It is estimated that this area of solar PV glazing would generate some 6900KWh
of electricity at an approximate extra over cost of installation of £16000 (the
glazing costs are incorporated in the previous estimates for re-roofing) and it is
estimated that payback would be achieved after a period of some 14 years.
8.10. It is not recommended that solar PV glazing is introduced into the curtain walling
as very little benefit would accrue and the payback period would be similar to the
roof glazing.
8.11. A summary of the anticipated electrical generation, cost and payback period is
tabulated below: -
Electrical generation KWh
Cost £ Payback years
Existing system re-fixed
28000 15000 -
New roof solar PV 20000 40000 13
Solar PV glazing 6900 16000 14
TOTAL 54900 71000
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8.12. The proposed solar PV applications for this building are shown on the plan in
Appendix B, this is, however subject to a calculation checks to determine the
integrity of the roof (and supporting structure) depending upon the system chosen
by the successful contractor, should these works proceed.
8.13. No allowance has been made for the cost of any structural works that may be
required as a result of solar PV panel installation on the roofs.
A P Williamson BSc (Hons) CEng MICE MIStructE FIOR
Page 22 of 24 30.01.2015
APPENDIX A – Plan and elevations
Plan of Spectrum Centre – Glazing Roof sheeting
Page 23 of 24 30.01.2015
North elevation – Glazing Roof sheeting
South Elevation
East Elevation
West Elevation
Page 24 of 24 30.01.2015
APPENDIX B – Proposed solar PV plan
