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www.polysolar.co.uk

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PREFACE

Re-thinking the building envelope.

The integration of renewable energy systems into architectural design is a topical and

prevalent theme that presents opportunities for innovative approaches to urban design and

engineering while meeting current and future building requirements.

As consultants and drivers of innovation, architects and design engineers have a decisive role

to play in recognising the advantages and potential of building-integrated photovoltaics

(BIPV) and applying them to meet specific project requirements. This involves combining

architectural, engineering design, and economic considerations within the context of a

buildings total energy consumption.

Polysolar is a developer, manufacturer and distributor of next generation thin-film photovoltaic

glass and innovative solar glazing solutions. Our products are designed to meet project-

specific architectural requirements and place us well throughout the design, planning and

construction of energy-optimised solar solutions for the building envelope.

This document acts as a broad guideline for relevant projects and aims to provide an overview

of the design potential of BIPV and the factors that influence planning and Building Regulation

considerations.

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TABLE OF CONTENTS

PREFACE ........................................................................................................................................................................ 3

TABLE OF CONTENTS .................................................................................................................................................... 4

TABLE OF FIGURES ......................................................................................................................................................... 6

1 Defining BIPV ......................................................................................................................................................... 7

2 Building Integrated Photovoltaics ..................................................................................................................... 8

2.1 Technologies ................................................................................................................................................... 8

2.1.1 Crystalline Silicon ................................................................................................................................... 8

2.1.2 Thin-film Modules ................................................................................................................................... 8

2.1.3 New Developments .............................................................................................................................. 9

2.2 Efficiency & Yield ............................................................................................................................................ 9

2.3 Multi-functionality ......................................................................................................................................... 12

2.3.1 Light & visual ........................................................................................................................................ 12

2.3.2 Sun protection ..................................................................................................................................... 12

2.3.3 Architectural design ........................................................................................................................... 13

2.3.4 Thermal Control ................................................................................................................................... 13

2.3.5 Thermal insulation ............................................................................................................................... 13

2.3.6 Weather protection ............................................................................................................................ 13

2.3.7 Sound insulation .................................................................................................................................. 14

2.4 Module Design .............................................................................................................................................. 14

2.4.1 Transparency ....................................................................................................................................... 14

2.4.2 Colour.................................................................................................................................................... 14

2.4.3 Glazing Types ....................................................................................................................................... 15

2.4.4 Cell Contacts ....................................................................................................................................... 15

3 BIPV Applications................................................................................................................................................ 17

3.1 Carports ......................................................................................................................................................... 17

3.2 Street Furniture .............................................................................................................................................. 17

3.3 Sheds and Barns ........................................................................................................................................... 17

3.4 Conservatories .............................................................................................................................................. 18

3.5 Curtain wall & rain-screen façades .......................................................................................................... 18

3.6 Canopies ....................................................................................................................................................... 18

3.7 Skylights, atriums ........................................................................................................................................... 18

3.8 Greenhouses ................................................................................................................................................. 18

3.9 Road barriers ................................................................................................................................................. 19

3.10 Solar automotive ..................................................................................................................................... 19

4 BIPV Design Guidelines ...................................................................................................................................... 20

4.1 Design Strategies .......................................................................................................................................... 20

4.1.1 Architecture ......................................................................................................................................... 21

4.1.2 Urban Space ........................................................................................................................................ 21

4.1.3 Landscaping ........................................................................................................................................ 21

4.2 Glass Layer Structures .................................................................................................................................. 22

4.2.1 Glass/Glass-PV Modules .................................................................................................................... 22

4.2.2 PV Thermal Insulation Double-glazing ............................................................................................. 22

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4.2.3 Glass/film-PV Modules ........................................................................................................................ 22

4.3 Environmental Variables ............................................................................................................................. 23

4.3.1 Orientation ........................................................................................................................................... 23

4.3.2 Low-light Performance and Spectral Sensitivity ............................................................................ 24

4.3.3 Shading ................................................................................................................................................. 24

4.3.4 Temperature ........................................................................................................................................ 25

5 Economic Considerations ................................................................................................................................. 26

5.1 Panels in construction ................................................................................................................................. 26

5.2 CO2 Emissions and Regulations ................................................................................................................. 26

5.3 Feed-in Tariff .................................................................................................................................................. 26

6 Mounting System and Installation ................................................................................................................... 28

6.1 Linear Mounting Systems ............................................................................................................................ 28

6.1.1 Mullion-transom façades ................................................................................................................... 28

6.1.2 Structural sealant glazing (SSG) ....................................................................................................... 29

6.2 Point-Fixing systems ...................................................................................................................................... 29

6.2.1 Drilled spot fitting ................................................................................................................................. 30

6.2.2 Clamp fixings ....................................................................................................................................... 30

6.2.3 Undercut anchor fixings ..................................................................................................................... 30

6.3 Installation Situations.................................................................................................................................... 30

6.3.1 Sloping glazing .................................................................................................................................... 31

6.3.2 Vertical glazing .................................................................................................................................... 32

6.3.3 Glass barriers ........................................................................................................................................ 32

6.3.4 Walk-on glazing ................................................................................................................................... 32

6.3.5 Step-on glazing ................................................................................................................................... 33

7 Electrical System ................................................................................................................................................. 34

7.1 Solar panel .................................................................................................................................................... 34

7.2 Solar Array ..................................................................................................................................................... 34

7.3 Connections .................................................................................................................................................. 34

7.3.1 Serial connections............................................................................................................................... 34

7.3.2 Parallel connections ........................................................................................................................... 34

7.4 DC and AC load-break switch .................................................................................................................. 35

7.5 Inverter ........................................................................................................................................................... 35

7.6 AC load-break switch ................................................................................................................................. 35

7.7 Generation meter ........................................................................................................................................ 35

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TABLE OF FIGURES

Figure 1: Crystalline Silicon Module ........................................................................................................................... 8 Figure 2: Polysolar thin-film a-Si Transparent Glass ................................................................................................. 9 Figure 3: Polysolar Colourless PS-CT glass ................................................................................................................. 9 Figure 4: Polysolar BIPV thin-film facade ................................................................................................................ 10 Figure 5: PV performance at varying light intensity ............................................................................................. 11 Figure 6: PV performance at different temperatures .......................................................................................... 11 Figure 7: The multiple functions of BIPV as a building material.......................................................................... 12 Figure 8: Horticultural greenhouse utilising transparent PV panels ................................................................... 13 Figure 9: Insulation benefits of Polysolar Glass ...................................................................................................... 13 Figure 10: PV weather canopy ................................................................................................................................ 13 Figure 11: Polysolar Transparent PV walkway, Barbican ..................................................................................... 14 Figure 12: Thin-film a-Si Modules .............................................................................................................................. 15 Figure 13: Kromatix colour coatings on PV panels ............................................................................................... 15 Figure 14: PV panels being used as canopies for example in petrol stations ................................................. 16 Figure 15: Carport system ......................................................................................................................................... 17 Figure 16: Polysolar PV Glass Bus Shelter Canary Wharf, London ...................................................................... 17 Figure 17: Domestic garage roof ............................................................................................................................ 17 Figure 18: Polysolar PV Glass Hathersage swimming-pool solarium ................................................................. 18 Figure 19: Polysolar Curtain wall (middle) & rainscreen façade (left and right) ............................................ 18 Figure 20: Sainsbury’s Leicester canopy ................................................................................................................ 18 Figure 21: Polysolar Skylight ...................................................................................................................................... 18 Figure 22: Domestic greenhouse with PS-C panels ............................................................................................. 19 Figure 23: Sound dampening road barrier ............................................................................................................ 19 Figure 24: Solar roof on a car ................................................................................................................................... 19 Figure 25: Rainscreen Façade ................................................................................................................................. 20 Figure 26: CIS Tower, Manchester, UK - Retrofit PV Façade ............................................................................... 20 Figure 27: Glass Facade perfect for BIPV installations ......................................................................................... 21 Figure 28: Glass/Glass module structure ................................................................................................................ 22 Figure 29: Thin-film PV façade ................................................................................................................................. 22 Figure 30: Insulated PV glazing ................................................................................................................................ 22 Figure 31: Polysolar skylight ....................................................................................................................................... 22 Figure 32: Thin-film PV as windows .......................................................................................................................... 24 Figure 33: Shading due to environmental factors ................................................................................................ 24 Figure 34: Modules in series ...................................................................................................................................... 25 Figure 35: Modules in parallel .................................................................................................................................. 25 Figure 36: Return on investment .............................................................................................................................. 27 Figure 37: Installation of Polysolar transparent modules ..................................................................................... 28 Figure 38: Linear mounting systems ........................................................................................................................ 29 Figure 39: Ventilated rainscreen cladding system and fixing ............................................................................ 29 Figure 40: Different Point Fixing systems ................................................................................................................. 30 Figure 41: Mounting panels ...................................................................................................................................... 31 Figure 42: Freestanding protective barrier ............................................................................................................ 32 Figure 43: Polysolar glazed roof ............................................................................................................................... 33 Figure 44: Solar PV Diagram ..................................................................................................................................... 36 Figure 45: Curtain wall structure .............................................................................................................................. 36

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1 Defining BIPV

Building-integrated photovoltaics (BIPV) refers to

the concept of integrating photovoltaic

elements into the building envelope,

establishing a symbiotic relationship between

the architectural design, structure and multi-

functional properties of the building materials

and the generation of renewable energy.

The photovoltaic (PV) modules thus replace

conventional construction materials, such as

glass, taking over the function that these would

otherwise perform whilst also including the

additional function of energy production.

Although this idea is not a new concept, it has

until recently not been widely adopted due to

the extensive planning and architectural

challenges and an inertia in the building trade,

one that Polysolar aims to change.

In principle, BIPV can be used in all parts of the

building envelope. Although roof surfaces are

currently the preferred area for installing PV

elements due to their advantageous irradiation

values, façades, windows and other structures

often offer greater potential.

The ratio of façade surface area to roof surface

area increases with the building height. In

addition, the available roof area is often

reduced due to the installation of facilities and

superstructures, meaning BIPV façades are of

particular value in high-density urban centres.

Current incentives and regulations have largely

driven PV installations to date, predominantly

consisting of building-applied photovoltaics

(BAPV) systems where the PV is an addition

rather than performing any other function, for

purely financial returns.

The existing process of constructing buildings

and then bolting on renewable energy

generation devises is neither a good use of

material resources nor does it achieve the best

aesthetic, functional or cost-effective

outcomes. At Polysolar we believe that “bolt-

on” PV is a ‘stop gap’ measure until full

integration within the fabric of the building

becomes the norm. With a considered upfront

systems approach, there is no technical reason

why BIPV could not be integrated into any new

build.

Building integrated PV (BIPV) offers the potential

to make micro renewable energy generation

costs competitive with fossil fuels. By substituting

conventional building envelope construction

materials for solar PV modules, the additional

installed cost of the PV energy generation

element is marginal within the total build and in

some cases cheaper on a square meter basis.

Add on the multi-functional benefits afforded by

PV glass and the additional costs can become

non-existent. For these reasons, we believe the

future for PV is BIPV.

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2 Building Integrated Photovoltaics With regards to the aesthetics of the building, a PV

module should have a homogeneous

appearance and either blend discretely into the

overall design or dominantly shape it.

The appearance of the PV module is essentially

determined by the type of technology used in the

PV cell and by the design possibilities offered by

the selection of materials used in the module.

2.1 Technologies

The PV market, as an innovative and rapidly

growing industry, offers a widening range of

different technologies. Generally, these can be

divided into two main groups based on the type of

manufacturing technology, namely crystalline

cells and thin-film cells. In addition, there are

several new technologies under development

based on organic (man-made) compounds and

nano-structures that offer the possibility of cheaper

and more functional photovoltaic materials in the

future. Polysolar are leaders in next generation PV

modules through the development of organic

polymer (plastic) solar cells for application as fully

transparent colourless photovoltaic windows.

2.1.1 Crystalline Silicon

Crystalline solar cells, derived from growing silicon

crystals or ingots then slicing them into

semiconductor wafers, usually consist of

approximately 150 X 150 mm (6” X 6”) square

plates with a metallic blue or black surface that is

subdivided by silver-coloured contact grids, which

collect the current. There are two key types; mono-

crystalline and poly-crystalline cells. The former

being hexagonal and higher efficiency and the

latter being square and slightly lower efficiency.

Special anti-reflective coatings can be applied to

create other metallic shades/colours. Modules are

created by connecting several silicon cells to form

larger strings.

For semi-transparent modules, light transmission

through the panels can be achieved and adjusted

by altering the spacing between the cells. Since

the size of the cells is not variable, any change in

the module size leads to a change in the overall

light transmittance or results in a suboptimal

arrangement of cells. Various shapes and pattern

variations can be achieved.

2.1.2 Thin-film Modules

Thin-film modules consist of a semiconductor, a

few micrometres thick, typically installed on

conductive glass by means of vapour deposition

with a metal backed structure. The resulting

coating is then subdivided into individual thin linear

cells; these cells are broken up by metallic or

transparent lines. The size of the modules is

predetermined by the size of the carrier plate and

is therefore difficult to divide into smaller segments.

Bespoke panel sizes can be achieved by

depositing on a smaller area of conductive glass or

by laminating multiple panels together.

Semi-transparency can be achieved in some thin-

film panels by selective removal of the PV module

material layers using laser ablation. This creates a

pattern in the panel and allows light to pass

through the gaps. By nature of removing the active

material, there is a proportional reduction in

power.. Various levels of clarity can be achieved

with finer patterning and more ablation.

The approach undertaken by Polysolar in contrast

to other companies is to utilise a variety of thin-film

materials to offer direct functionality. These include

amorphous silicon a–Si, micro-morph l a-Si/μc-Si

and Cadmium telluride CdTe.

2.1.2.1 Amorphous silicon (aSi)

This technology utilises the equivalent of powdered

silicon in very small quantities. This is vacuum

deposited along with transparent, conductive

oxides on both glass surfaces with the active PV

material between as a semiconductor. The glass is

then laminated together as a sandwich to create

a uniquely translucent module.

The PV panel allows around 20% light (T200-700)

transmission across the whole surface, without

requiring additional processing or material

wastage. Combined with our mass production

process, this makes the Polysolar PV Panels cost

comparable with conventional crystalline silicon

modules.

Figure 1: Crystalline Silicon Module

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The modules themselves are tinted and uniquely

work on both sides, making them ideal in situations

where there is reflective light on the underside.

Polysolar also produces opaque versions of the

same module design, using the addition of a white

paint interlayer in between the laminate so the

back of the module appears as white glass and

the light is reflected internally giving a 10% uplift in

panel performance.

2.1.2.2 Micromorph (Si/µc-Si)

This technology consists of a multijunction structure

of two layers of amorphous silicon and

microcrystalline silicon. The a-Si absorbs in the blue

light spectrum and the μc-Si absorbs in the red,

with the result that the panel performance per

square metre is improved significantly. The

appearance of the opaque panels is black, while

the transparent version appears colourless.

2.1.2.3 Cadmium Telluride (CdTe)

Polysolar also uniquely manufactures a transparent

thin-film PV glazing based on cadmium telluride,

CdTe. This offers significant performance

improvements over a-Si and even micromorph

panels. Absorbing light across the spectrum, the

colourless transparency is achieved through laser

ablation to deliver a fine pixelated effect.

Polysolar also works alongside other specialist PV

and glass manufacturers, utilising other PV

technologies to achieve the highest aesthetic,

structural and performance requirements our

clients require. Polysolar can therefore offer

product variants to enable architecturally unique

bespoke BIPV solutions for most applications.

2.1.3 New Developments

Whilst to date it is not possible to create completely

clear modules, Polysolar is working on the next

generation of organic polymer solar cells (OPV)

that capture light consistently across the light

spectrum as well as in the non-visible spectrum to

create truly transparent colourless PV Glass for the

future.

2.2 Efficiency & Yield

To compare the different types of cell technology

the rated yield of each module type is determined

based on standardised measurements, usually

conducted under ‘standard test conditions’ (STC).

This involves applying a light source of 1000 W per

m2 vertically to the modules, at an ambient

temperature of 25° Celsius. For the purpose of this

measurement, the spectral composition of the light

is 1.5 AM (air mass factor)..

.

The output measured under these conditions

determines the solar element’s rated module

output that the manufacturer is obliged to state.

The ratio of the applied radiation (1000 W/m2) to

the measured values gives the efficiency of the

solar module.

Generally, the older and already highly developed

crystalline technologies still provide the highest

commercially available efficiency values of12% to

17% for polycrystalline modules and up to 20% for

monocrystalline modules. The efficiency of thin-film

technologies currently lies below these values,

typically ranging from up to 7% for amorphous

silicon and up to 12% for CdTe modules.

Current research promises further optimisation of

the yield per unit area of solar elements and these

are rising by around 1% per annum on average.

Importantly, the STC efficiencies of different PV

panelsdo not necessarily reflect the yield, or

energy output that can be derived over a year in

a given location or position.

Figure 2: Polysolar thin-film a-Si Transparent Glass

Figure 3: Polysolar Colourless PS-CT glass

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In reality, PV installations are not exposed to

constant test conditions and consequently there

are significant variations in the amount of energy

that they actually generate.

Photovoltaic technologies performances vary in

different light intensities and temperatures. High

performance crystalline modules are optimised for

1000 W/m2 radiance but their performance tails off

significantly in lower irradiance. Thin-film

photovoltaics technologies in contrast tend to

operate optimally at 700 - 800 W/m2 radiance and

continue working down to very low radiance

levels. Unlike crystalline modules which require

direct sunlight, thin-film works in ambient and

reflected light as the individual crystals bounce the

light around within the cell.

Polysolar’s thin film modules, for example, operate

down to ~10% of sunlight ensuring they maintain

their efficiencies even on the dullest days, working

even indoors from artificial light.

The performance differentiation in different light

levels is not only important when considering the

position of the project geographically, but also in

relation to where on a building the PV panels are

sighted. PV panels on a vertical façade will receive

lower light levels than those optimally angled on a

roof. Equally, those facing north will receive less

direct light than those facing south and hence

different technologies need to be considered in

relation to the full spectrum performance they will

receive.

Conventional crystalline silicon modules tend to

need to be optimally positioned to maximise solar

radiance to operate effectively. Thin film

technologies on the other hand can often

effectively be positioned on the vertical or non-

south facing positions where they utilise ambient

light rather than direct sunlight.

Figure 4: Polysolar BIPV thin-film facade

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Figure 6: PV performance at varying light intensity

Figure 5: PV performance at different temperatures

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Further, while all PV cells tend to perform better at

lower temperatures, crystalline silicon cells can see

dramatically reduced performance in high

temperatures, while thin-film technologies tend to

be less affected by higher temperatures. Indeed,

there is a general avoidance of using crystalline

silicon modules in the tropics and hot desert

regions due to the high ambient temperatures

significantly impacting energy yields.

Temperature co-efficient data of the panel

technology is therefore an important consideration

when considering a BIPV project. The co-efficient

of temperature / power (%/°C) of c-Si crystalline

modules is -0.4 to -0.5 %/°C, while the thin-film a-Si

equivalent is -0.1 to -0.2 %/°C.

As panels may be mounted directly onto insulation

or offset slightly for airflow ventilation, these factors

need to be considered as module efficiency can

drop by more than half if the incorrect technology

is used. Even in the UK summer, pitched roof

mounted module temperatures can reach over 70 °C, significantly reducing performance. In contrast,

thin-film panels, and in particular, transparent or

double-glazed panels, can avoid the concerns

with high temperature build up and hence their

performance can be maintained even where

limited ventilation is possible.

2.3 Multi-functionality

Due to their mechanical properties, PV panels can

perform the functions of the building envelope in

addition to generating emission-free energy, thus

replacing/substituting for conventional

construction materials.

The extent of this multi-functionality as a building

material is determined by the design of the panel

structure, which in turn defines the technical,

economic and architectural design aspects of the

project.

By taking on additional functions, solar

construction elements can be used for various

applications in buildings, and can even be used as

a substitute for separate systems, such as shading

systems and Brise Soleil, that would otherwise be

required. Such substitutions therefore make BIPV

systems cheaper than traditional materials and

even produce a return on investment. Thus,

despite the additional electrical system and PV

material costs, building-integrated PV systems can

be in some circumstances significantly more cost-

effective than traditional construction materials.

2.3.1 Light & visual

The relationship between the interior and exterior

world is of great importance in architecture. The

use of translucent or semi-transparent solutions

combines shading with light and visual clarity with

screening. In contrast to purely opaque solutions,

the architectural design potential is increased here

to perform the function of a window. Panels are

available in semi-transparent, opaque or even a

variety of colours.

2.3.2 Sun protection

The PV panels provide sun protection, delivering

shading and glare control. The transparency can

be varied to provide the desired degree of light

transmission in accordance with a targeted

design.

Polysolar modules absorb light in the ultraviolet

(UV) wavelengths that causes bleaching and

degradation of physical objects, scorching in

plants, and sunburn. Polysolar panels have even

been proved to aid healthy plant growth.

Figure 7: The multiple functions of BIPV as a building material

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2.3.3 Architectural design

The wide range of designs of PV panels makes it

possible to use them as architectural design

elements and can be incorporated and managed

during the design stage.

Furthermore, the innovative nature of the panels

adds to the overall image of the building and

contributes to the impressive atmosphere within.

2.3.4 Thermal Control

The temperature of a photovoltaic module can

increase significantly when the module is exposed

to radiation. The heat that the modules then

radiate into the environment can be harnessed to

provide heating or can be utilized to enhance

passive ventilation systems.

A further attribute of transparent thin-film solar

panels is in the regulation of thermal gain within a

building. The conductive coatings on the glass also

acts to reflect the infrared light spectrum,

performing the function of low emissivity glass as

used in conventional commercial office windows.

This reduces the thermal gain (g-values) also

reflecting the heat back within the building to

ensure a more consistent temperature over the

day and seasons. Heat gain is also reduced by a

combination of shading and absorption,

converting some of the light to electricity.

2.3.5 Thermal insulation

Depending on their thickness, the multi-layer glass

structures of PV modules can be used to provide

thermal insulation. In addition, most modules can

also be integrated into double or triple glazing units

or used as alternative secondary glazing as front

cladding for curtain or roof insulation elements. An

air-filled double glazed Polysolar transparent

module has u-values of 1.2 W/m2.K and as low as

0.9 W/m2.K with argon-filled double glazed units

making their thermal performance superior to most

conventional glazing systems.

2.3.6 Weather protection

The glass structure of PV modules naturally provides

weather protection. With the correct choice of

glazing layers or films in combination with the

building-integration mounting system, PV panels

can provide rain-proofing, wind-proofing, wind

load resistance and ageing resistance as well as

offering residual structural integrity to the building.

Figure 8: Horticultural greenhouse utilising transparent PV panels

Figure 10: PV weather canopy

Figure 9: Insulation benefits of Polysolar Glass

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2.3.7 Sound insulation

PV panels can reflect or attenuate sound

depending on their construction. For this reason,

they can also be used as sound protection

elements. PV façades or roof elements already

possess sound insulating properties thanks to their

multi-layer structure, and the module design can

be adapted to meet specific local sound insulation

requirements. The sound reduction index can be

adjusted by increasing the thickness of the glazing

and by using asynchronous cover layers and

specific intermediate layers, such as

polycarbonate.

2.4 Module Design

Solar BIPV panels are generally available as

laminates made of glass/glass or metal/plastic film.

As a rule, façade and overhead glazing systems

use glass laminates only, while roofing modules are

glass/metal film or plastic/metal film.

In addition to providing protection for the solar

cells, these laminate elements can also meet

structural and design requirements.

Various parameters should be considered when

assessing BIPV suitability in a, such as:

❖ Module size

❖ Module shape (e.g. rectangles or special

shapes)

❖ Covering glass

o Glass quality

o Strength

o Structure

o Coating

o Colour

o Tinting

o Patterning

❖ Cell background or reverse side of module

❖ Transparency arrangement of solar cells in the

module, patterning, or material transparency

to give percentage light transmission

❖ Interconnections: Wiring and connectors

❖ Multi-layered superstructures such as insulated

glazing

❖ Cell colour

❖ Module aesthetics: uniformity, framing, cell

lines, etc.

2.4.1 Transparency

Transparency or semi-transparency can be

achieved in different types of PV modules using

different technologies.

The effect of transparency is commonly achieved

in the PV module by the combination of

transparent unoccupied areas and a pattern of

opaque solar cells. The arrangement and

distribution of the solar cells within the module thus

controls the degree of transparency. This makes it

possible to create interesting and innovative light

effects. If the module is required to have less

transparency, the intermediate areas not filled with

cells can also be coloured.

There are broadly three conventional approaches

to achieve semi-transparency. One is to take

individual crystalline silicon cells and embed them

in a glass laminate. The cells can bespaced

accordingly to allow the light through. The

alternative approach is taking thin-film glass

modules prior to lamination and patterning the

module using a laser to ablate (remove) the active

layer, allowing the light to pass through. The third

approach taken by Polysolar is to achieve

transparency of the active PV material by the

adoption of ultra thin-film deposition of the active

PV materials with two layers of transparent

conductive coatings. While the resultant module is

tinted, light can pass through the surface of the

module to create of transparent PV glass module

without loss in performance caused by ablation of

the materials or spacing the cells.

2.4.2 Colour Variations in the colour of solar modules can be

achieved. Conventional solar cells are generally

black or blue in the case of crystalline silicon and

brown or black with thin-film.

To achieve colour effects that differ from the cell

colour, coloured laminates, coatings or films can

be used. This makes it possible to create interesting

effects such as logos on PV modules or colours that

match the existing building.

Figure 11: Polysolar Transparent PV walkway, Barbican

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The following methods can be used for colouring

solar panels:

❖ The use of coloured glass

❖ Use of coloured polycrystalline modules

❖ Glass with full area print (glass enamel) with

various patterns

❖ The application of a coloured laminate film

(low resistance) in semi-transparent modules

❖ Refractive-reflective coatings such as Kromatix

These creative design measures on the surface of

the panels naturally result in a reduction in the sunlit

surface area or in the reflection of some of the

incident light. The output of the solar module is

therefore always reduced. For this reason, a

compromise between design and output must

always be found when designing coloured solar

panels. To minimise the reduction in efficiency, the

coverage rate of the colour printing, or the

intensity of the colouring, should be kept as low as

possible. That said, the trade-off for colour can be

only a 5% reduction in performance.

Polysolar currently offers a full range of colour

laminates and Kromatix coated thin-film tinted

panels (transparent and opaque). These are

designed to be complementary to local building

vernacular. We also have a transparent grey

module where printed designs and colours can be

incorporated into the module.

2.4.3 Glazing Types

While most solar modules have a fixed glass type in

their design, provided there are no process-related

limits, all available quality grades and types of glass

can be used for solar modules. This means that the

structural and safety requirements for specific

types of application can be met by using

toughened glass or different thicknesses of glazing.

To ensure optimum yield, the cover glass should

preferably be white glass with a low iron oxide

content and high transmission. The lower iron oxide

content also eradicates the typical greenish tint of

the glazing.

Using structured glass for the cover glass can also

increase the yield of a solar panel. The surface of

the structured glass is made up of wave-shaped,

rounded depressions that act as light traps. Some

of the radiation that would normally be reflected

into the environment and lost, is directed back into

the cell. This increases the amount of incident

radiation and can increase the output of the solar

modules by up to 3 %. From an architectural point

of view, however, the fascination of this type of

glazing lies in its matt appearance and non-

reflective surface. Similar looks can be achieved

though sandblasting to pattern the surface.

As most BIPV glazing is laminated, it tends to meet

the structural and safety requirements of overhead

glazing. Where additional strength is required,

Polysolar recommends either using a thicker or

strengthened back glass or even triple laminating

the unit to achieve the desired requirements – such

as balcony glazing.

Polysolar uses a mixture of standard float glass on

front of its modules as well as variety of heat

treated or tempered glass. It is important to

remember that if cut ‘dummy’ BIPV panels are to

be employed in the design that not all glass can

be cut onsite.

In addition, BIPV glazing panels can be double or

even triple glazed to achieve superior thermal

insulation values. Polysolar also offers double

glazed units with a full range of rear glass achieving

u-values of less than 1.0. Note that because of the

electrical contacts, automated double glazing is

usually not possible.

2.4.4 Cell Contacts

Electrically conductive contacts are required to

connect the individual cells and super cells within

the module. Often, these are made of conductive

materials such as copper and significantly affect

the appearance of the module. However,

depending on the type of technology used, these

electrical contacts can be made invisible if

required.

Figure 12: Thin-film a-Si Modules

Figure 13: Kromatix colour coatings on PV panels

16

Polysolar’s thin-film modules have the conductive

bus bars on the edge of the glazing module so are

non-visible. The connector blocks are either

housed on the back of the module or on the

edgeof the laminate for incorporation into window

frames.

Figure 14: PV panels being used as canopies for example in petrol stations

17

3 BIPV Applications

Since BIPV modules can be structured in many

ways, there is a correspondingly large variety of

possible applications for the integration of PV

systems in and on buildings. Solar PV cells can be

incorporated into just about any glass layer

structure, so that even walk-on glazing, bullet proof

glass and thermal insulation glazing systems are

possible.

Examples of possible and existing applications

include:

❖ Solar protection fins and louvres

❖ Sun protection panels and canopies

❖ Façade cladding - rain screens, curtain walling

& rear-ventilated façades

❖ Double glazed façades

❖ Translucent or semi-transparent windows

❖ Integrated Roofing

❖ Skylights

❖ Privacy protection panels

❖ Balustrades & fencing

❖ Sliding shutters

❖ Canopy roofs

❖ Street furniture

❖ Noise protection walls

❖ Greenhouses

❖ Advertising billboards

❖ And many more

By building with PV, unique and attractive

structures can be created that deliver form and

function.

3.1 Carports One of the biggest BIPV markets is for carports.

Here the PV panels are mounted onto a car park

canopy that both protects the vehicles and

passengers from the elements, but also provides a

large area on which to generate power. With the

advent of electric vehicles (EV); where the charge

points deliver free renewable electricity, these BIPV

car park canopies are set to grow significantly.

Polysolar has developed a range of canopies that

use both transparent and opaque PV panels as the

roof. With large scale installations, these can

deliver solar for less than £1.50/Wp installed.

3.2 Street Furniture The smart cities of the future will increasingly

incorporate stand-alone structures that generate

their own power. Examples of which are park

benches that can charge mobile devices. bus

shelters that power the information screens,

walkways that can be illuminated from batteries or

cycle shelters that can recharge electric bicycles.

3.3 Sheds and Barns Why stop at shelters when complete barns can be

built of PV panels enabling a low-cost construction

to a preformulated modular design;delivering not

only sufficient energy for the building but also

enabling export to the grid.

Figure 15: Carport system

Figure 16: Polysolar PV Glass Bus Shelter Canary Wharf, London

Figure 17: Domestic garage roof

18

3.4 Conservatories

The PV glass units replace the conventional

glazing, providing a weatherproof envelope,

reducing the thermal gain, and generating

electricity.

3.5 Curtain wall & rain-

screen façades Polysolar's photovoltaic glass panels are ideal for

incorporating into building façades due to their

frameless design and aesthetic finish. They are

more efficient at non-optimal angles than

crystalline silicon panels and so ideal for a vertical

mounting system. Panels can be incorporated into

a curtain walling framework or in a bonded

rainscreen system.

3.6 Canopies

Incorporating PV into canopies and walkways is a

great way of utilising what is often a large space

more productively. One advantage of using BIPV

in a canopy structure is that the PV has dual sided

operation, increasing the overall energy yield.

Petrol stations, carports and railway stations are a

few examples of idea candidates for this solution.

3.7 Skylights, atria With colourless, transparent PV options available,

skylights and glasshouses are an ideal way of

incorporating PV into a building. Transparencies of

up to 50%are available , making this solution both

aesthetic and functional. Polysolar works in

collaboration with leading glazing companies to

offer full solutions.

3.8 Greenhouses Greenhouses have also become an opportunity

for using BIPV, offering a large surface from which

to generate renewable energy whilst also forming

part of the structure. While conventional PV panels

have been deployed in greenhouses, Polysolar’s

transparent glazing directly replaces the

Figure 18: Polysolar PV Glass Hathersage swimming-pool solarium

Figure 19: Polysolar Curtain wall (middle) & rainscreen façade (left and right)

Figure 20: Sainsbury’s Leicester canopy

Figure 21: Polysolar Skylight

19

horticultural glass and in some cases, can improve

the plant yields through selective control of the

wavelengths of light and temperature control.

3.9 Road barriers

By dampening sound, Polysolar panels are ideal for

sound barriers along motorways or main roads.

3.10 Solar automotive

With solar panels on top of your car, you will never

run out of battery! The panels can be tailored to

the required aesthetic and structural components

of the vehicle, with retractability and transparency

an option.

Figure 22: Domestic greenhouse with PS-C panels

Figure 23: Sound dampening road barrier

Figure 24: Solar roof on a car

20

4 BIPV Design Guidelines

The design of a BIPV system tends to be a

more complex process than a standard

‘tack-on’ PV systemsince it is necessary to

reach a consensus between optimum

operating conditions for the photovoltaic

system, the architectural context, structural

requirements, economic considerations,

and building regulations.

The rated output data for the PV modules,

based on standardised measurements, is of

only limited relevance here and even more

restrictive in the case of standard assessment

procedure (SAP) calculations as the panels

are not optimally positioned and perform

differently to framed crystalline silicon panels

In the case of BIPV, it is more important to

carefully select the right system, to tailor the

design of the PV elements to suit the

requirements of the project, and to take

these elements into consideration at an

early stage in the planning process to

achieve electrically and architecturally

optimised systems.

Particular attention must also be paid to the

planning processes and to the allocation of

responsibilities before and beyond project

completion. The planning, design and

implementation of a building-integrated

system requires the cooperation of several

different trades, such as electrical installation

and façade construction specialists, which

traditionally have very little overlap during

the detailed design stage.

It is vital, therefore, that the services provided

by the different trades are precisely defined

and demarcated. Indeed, unlike

conventional PV array installations, BIPV

projects tend to utilise specialist contractors

that need to develop familiarity with PV

modules and their application.

As a basic principle, however, the steps and

questions described in more detail below

should be observed in the planning phase

and should be reflected in the design and

implementation:

❖ Design strategy

❖ Environmental variables

❖ Multifunctionality

❖ Construction system

❖ Installation situation

❖ Glass structures

❖ Module design

❖ Electrical components

❖ Economic aspects

4.1 Design Strategies The use of renewable energy sources in

architecture is by no means a new concept,

indeed the CIS Tower in Manchester (UK)

Europe’s largest BIPV vertical installation until

recently, dates to 2005.

The use of renewable energy sources in

buildings has, however, become more

Figure 25: Rainscreen Façade

Figure 26: CIS Tower, Manchester, UK - Retrofit PV Façade

21

topical recently, as architects, property

developers, and building users become

more inclined to consider issues of resource

conservation to meet building and planning

regulations along with rising energy bills and

awareness of environmental sustainability

and global warming.

Sustainable or energy-active systems in the

building envelope present the possibility of

meeting these requirements cost effectively

using innovative applications within the

context of the proposed building or

refurbishment project. The incorporation of

renewable energy systems in buildings is now

not only a necessity to meet regulations, but

offers the added advantage of providing a

return on investment from the building

envelope.

To integrate photovoltaic systems in a

sensitive and satisfactory way, architectural

and structural factors, as well as economic

considerations, must be considered and

reconciled at an early stage.

4.1.1 Architecture

In this context, architects have the important

task of recognising, as accurately and early

as possible, the advantages and the

potential of applications such as building-

integrated photovoltaics and of presenting

these to their clients in their role as consultant

and provider of ideas.

Photovoltaic systems can be integrated in

various ways to meet the energy

performance requirement of a building.

Depending on the desired appearance,

various strategies are employed that can

influence the overall effect of the building.

Common strategies include:

❖ Adjustment

❖ Contrast

❖ Dominance

❖ Dialogue

4.1.2 Urban Space

Aesthetically pleasing BIPV solutions are

particularly needed in the field of urban

development/Smart Cities. Many local

authorities are laying down design

regulations, either separately or in the

relevant development plan, which stipulate

requirements that must observed and met

before building permission is given.

Façades, visible roof areas and street

furniture determine the character of public

spaces. By designing BIPV systems to meet

the requirements, it is possible to incorporate

PV systems in the townscape in a visually

harmonious way. Coloured designs or

invisible fixings are often required in this

context.

The integration of PV systems in existing or

even protected buildings presents a

particular challenge, since the surfaces

available for PV integration are often limited

which is why building-integrated solutions

present an excellent opportunity.

4.1.3 Landscaping

The acceptance of PV systems is determined

to a large extent by their sensitive integration

in the landscape/cityscape. Conspicuous

systems can look strange and unfamiliar and

can be perceived to spoil the landscape.

This is particularly evident in the case of

typical free-standing systems that cover

large areas of land or ‘tack-on’ panels on

domestic rooftops that are designed and

installed taking only the economic aspects

of yield optimisation into consideration.

The fundamental issues of landscape or

cityscape integration relate to the type of

installation, the method used to fix the PV

elements, the aesthetics of the PV

technology used and, not least, the choice

of installation location.

If these parameters are controlled,

innovative and congruent solutions can be

Figure 27: Glass Facade perfect for BIPV installations

22

generated and even be used to enhance

landscape or cityscape and building design

features.

4.2 Glass Layer

Structures

The combination of solar cells with various

types of glass layer structures makes it

possible to use solar modules in many

different installation situations. Requirements

regarding overhead glazing and safety glass

can also be met in this way.

4.2.1 Glass/Glass-PV

Modules

Glass solar modules tend to comprise two

sheets of glass and use EVA (ethylene vinyl

acetate) or PVB as a bonding material. The

modules are classified as laminated glass,

due to their use of non-regulated bonding

materials with the solar cells sandwiched

within the panes. As laminated glass, they

are suitable for most façade and overhead

glazing applications.

Additional laminate layers can be applied to

perform additional functions, such as blast

proof glazing using multiple laminates and

polycarbonate interlayers. Furthermore,

Polysolar can create larger module sizes by

laminating multiple panels onto a large

expanse of glass. For colour effects, a

refractive glass from Kromatix can be

laminated onto the panels as a triple

laminate. Polysolar modules utilize the latest

PVB materials of 0.76 mm along with edge

sealing.

4.2.2 PV Thermal Insulation

Double-glazing

For the integration of solar modules into

transparent façades or roofs in occupied

buildings, the use of PV thermal insulation

glazing, or double glazing is often a standard

requirement. Both crystalline and thin-film

solar cells are suitable for the manufacture

of PV thermal insulation double-glazing.

Glass/glass PV modules can be used for

thermal insulation configurations. Fixed

either at the front or rear, dependent on

requirements (there will be a loss of

generating capability if additional glass is

placed in front of the panel), and on the

position of the module socket, these

modules include spacers, air or an insulating

gas and a single or laminated glass sheet.

A further possibility for overhead

applications is the use of solar modules with

three layers of glass. Modules with this type

of structure consist of two glass sheets

bonded together, as in the glass/glass solar

module units, plus an additional glass layer,

which is usually fixed at the front side of the

module. Such module constructions can be

used as walk-on glazing, although the same

limitations apply as for the glass/glass

module with regard to eligibility for approval.

4.2.3 Glass/film-PV

Modules

Figure 28: Glass/Glass module structure

Figure 29: Thin-film PV façade

Figure 30: Insulated PV glazing

Figure 31: Polysolar skylight

23

Glass-film modules are typically available as

standard conventional solar modules and

have the advantage of low module weight,

due to their combination of a lightweight

synthetic film on the rear side and a usually

thinner glass cover sheet. If toughened glass

is used for the cover glass and if the thickness

complies with the structural requirements,

then glass-film modules can also be used for

building integration. Indeed, glass-film

laminates are use in overhead roofing

situations.

4.3 Environmental

Variables

When designing a BIPV system, a

compromise must be reached between the

requirements of energy yield optimisation

and those of the architectural environment.

The rated output data for the PV modules,

which is based on standardised

measurements, can be misleading and is not

the most important criterion here.

The right type of technology for the

environment in question is more important.

Often, the less efficient thin-film PV

technologies represent the best choice ,

particularly in situations with suboptimal

environmental variables.

4.3.1 Orientation

The amount of incident solar radiation on a

surface of a PV module depends on its

orientation and angle of inclination. The

optimum angle of inclination varies

according to the latitude of the installation

site; the further the distance from the

equator, the steeper the optimum

installation angle. In Northern Europe,

surfaces that face south and are set at an

angle of around 35° to the horizontal receive

the maximum possible solar radiation.

However, slight deviations in angle, between

20° and 45°, and slight displacements to the

east or west often result in only minor losses in

radiation.

In the case of BIPV systems that are arranged

according to architectural criteria, optimal

positioning of the modules is rarely possible.

Nevertheless, good power yields can still be

achieved even with suboptimal alignments,

provided that the characteristics of the PV

modules allow this. Modules that perform

well in weak and diffuse light, for example,

can be used to good effect in situations

where the orientation is unfavourable.

Thin-film solar modules possess these

properties of operating in non-optimal light

and regularly generate higher yields in

suboptimal positions when compared to

crystalline systems. The use of thin-film

modules is recommended in situations

where there is ambient light and a significant

proportion of diffuse light due to reflection

and light scattering.

Further, different types of crystalline silicon

modules are available with better ambient

light capture or temperature coefficients.

Consequently, despite less than optimal

positioning in the vertical, façades represent

an excellent economic opportunity for PV

systems. They can be found in all types of

structures across the globe and, in contrast

to free-standing, open-field facilities, they

generate electricity in the immediate vicinity

of the user without the power losses

associated with transport and storage.

In urban settings, building façades represent

the greater area available for PV as high-rise

buildings have a much greater proportion of

façade area than roof area. The incident

solar radiation on south-facing vertical

façades in the UK is more than 80% of that of

a horizontal surface and is therefore well

suited to BIPV. Further reflection of light and

higher level of ambient light in cities can

make facades the key area of power

generation.

Yet, while roof topsgenerally offer a higher

energy potential, much of the available

area is already taken up by plant and

equipment for ventilation and air-

conditioning. Screening these areas

however provides further opportunities for

BIPV.

In Sheffield, UK, (which is classified as the

centre of average UK solar radiation),

Polysolar is currently having its modules

independently and publicly tested by

Sheffield University Solar Farm, one can

expect to generate 850-1000kWh per kWp of

solar electricity. http://www.solar.sheffield.ac.uk/panel-data/

24

4.3.2 Low-light

Performance and

Spectral Sensitivity The sun delivers enough energy in one day

to power the earth’s entire energy

requirements for over a year. This direct light

is ideal for most solar modules, and highly

efficient silicon solar cells are very good at

converting this energy to electrical power.

The direct sunlight is scattered, however, by

water vapour, dust and soot particles as it

reaches earth and is reflected from the

objects it strikes. This results in indirect or

diffuse light. The ability of solar cells to

convert diffuse or scattered light into energy

is referred to as low-light behaviour.

Thin-film solar modules demonstrate higher

efficiency in low light and produce greater

relative energy yields in comparison with

crystalline systems. They are therefore

recommended for applications with a

significant proportion of diffuse light and in

cloudy or dull weather climates. They also

enable suboptimal or even north facing

façades of buildings to be included in the

BIPV project.

The sun’s spectrum ranges from short

wavelength UV light to long wavelength

infrared light. Different solar cells react

differently to the different wavelengths of

the sunlight.

In contrast to crystalline cells, which absorb

primarily long wavelength radiation (red

light spectrum), thin-film solar cells can

absorb a wide spectral range. In diffuse light,

there is therefore less difference in efficiency,

since the short wavelength blue light is

absorbed well by the thin-film solar cells on

cloudier days or when the sun is low in the

sky. Polysolar offers a range of technologies

which vary in their spectrum absorption and

efficiencies.

4.3.3 Shading

Shading can significantly affect the yield of

a PV system. It can have many different

causes, such as vegetation, neighbouring

buildings, layers of dirt, self-shading due to

construction elements, or overhanging parts

of the mounting system. This shading can

also change overtime due to plant growth,

new buildings or dirt build-up.

Such sources of shade can be minimised by

careful planning to maximise the incident

solar radiation. Simulations of the daily and

yearly path of the shadows can be carried

out to enable the position of the solar

modules and the orientation and structure of

the building to be optimised accordingly. If

shading cannot be completely avoided, its

effects can be mitigated by using the

appropriate module technology, module

design and the electrical connection of the

modules best suited to the environment.

A key difference between crystalline silicon

modules and thin-film technologies is their

shade resistance due to string length. Thin-

film modules are designed to be high

voltage and so are linked in parallel rather

than long series strings meaning if one

module is shaded, the rest of the system is

not affected. This effect can be replicated

on crystalline modules with the use of micro-

inverters placed on each module to achieve

a parallel connection. In BIPV applications,

this is important as few building surfaces offer

long, uninterrupted facings for long series

linked arrays and therefore achieving the

required voltage levels to optimise a system

Figure 32: Thin-film PV as windows

Figure 33: Shading due to environmental factors

25

can prove difficult.

When linking modules in series, shading of

one module will lower the performance of

the entire string.

In contrast by linking in parallel, one module

being shaded does not affect the

neighbouring modules. This effect can be

achieved with the use of high voltage

modules or micro-inverters.

4.3.4 Temperature One feature of PV modules is their tendency

to increase in temperature rapidly, causing

a reduction In output. The output losses vary

depending on the type of cell technology.

The losses from silicon cells are

approximately 0.5 %/oC, which can have a

significant impact on array performance

and equates to more than twice the amount

lost by most thin-film modules. Polysolar

modules are Pmpp -0.21%/oC.

This temperature coefficient effect must be

considered since the standard output

measurement for solar modules is taken at 25

°C, whereas even in the UK modules

temperature commonly reach 55 °C – 70 °C

on a Summer’s day. From an energy yield

point of view, , it would be beneficial to

increase the ventilation to keep the module

temperature as low as possible. The different

module temperature issues mean that with

thin-film modules, you can insulate directly to

back of the module, thus avoiding the need

for additional ventilation. Additionally, the

temperature differentiation of a module can

be incorporated into the whole building’s

thermal control system as a passive

ventilation system.

Thin-film PV is often specified in hot climates

to overcome the temperature issues. With

crystalline silicon cells, a further issue to

consider is the thermal characteristics of

different elements of the module. For

example, in double glazed units with

embedded cells, the temperature

differential and differences in thermal

expansion can cause damage if poorly

manufactured.

Figure 34: Modules in series

Figure 35: Modules in parallel

26

5 Economic Considerations A common misconception is that the costs

for BIPV systems are significantly higher than

those for standard PV systems. New

technologies, manufacturing processes,

and component standardisation have

reduced the cost to a comparable level with

conventional PV systems.

Yet, the architecturally compatible design of

BIPV elements, using application-specific

module structures and high-quality

appearance, results in a corresponding

increase in value.

When considering the economic factors,

therefore, functional and architectural

contributions must be considered, as well as

the savings from electricity generation. Since

BIPV systems are used in place of other

construction components, the cost of

procurement and installation of these

components can be subtracted and offset

from the PV system.

Furthermore, in addition to the remuneration

received for the solar energy generated, this

energy can also be included in the energy

balance calculation for the building, in

accordance BREEAM and other regulations,

meaning costs for alternative energy

efficiency measures can be avoided. Further

effects, such as the impression that the

building makes due to its manifest

environmental awareness, can also add

value and shape its image. Therefore, it is not

unusual for the economic viability of a BIPV

system to be determined by its architectural

integration.

5.1 Panels in

construction Solar modules that are integrated into the

architecture of a building replace other

essential elements of the external skin, such

as façade cladding or shading elements,

with respect to design and function. To

achieve this, the structure of the BIPV

modules is specially designed to perform the

specific function(s) required.

When considering issues of economic

efficiency, the value of the construction

elements replaced by the modules can be

subtracted from the overall investment. To

profit from these economic benefits, this

construction component character must be

considered in the initial design phase.

Depending on the type of application, the

value of the replaced components can be

decisive with respect to the marginal

additional or even reduced cost of the

system.

5.2 CO2 Emissions

and Regulations Photovoltaic systems are extremely

environmentally friendly, since the amount

of energy they generate is significantly

higher than the amount used in the

manufacture. A further environmental

aspect is that PV installations require no fuel

and consequently emit neither dirt nor CO2.

This means that for every kilowatt-hour, the

emission of approximately seven tonnes of

CO2 is avoided. The reduction of CO2

emissions is regarded as one of the most

important measures required to combat

climate change. Today’s CO2 emissions

stem mostly from the construction and

operation of buildings. BIPV solutions are

helping to resolve this conflict by making

sustainable and emission-free energy

conversion possible at the point of use.

The combination of clean sources of

electricity, energy-efficient devices and the

expedient management of electricity

demands presents the potential for further

savings in the energy consumption of

buildings, both now and in the future.

This is also considered by regulators, which

allows the electricity supplied to the building

by the BIPV system to be included in the

calculations required to meet environmental

performance. Consequently, it may be

possible to dispense with other alternative

measures that may have been proposed for

optimising the building’s energy

consumption.

5.3 Feed-in Tariff

Most countries now provide for the

obligation of local energy supply companies

to purchase and provide remuneration for

electricity generated by PV systems. This

type of remuneration for photovoltaic

energy is paid per kilowatt-hour of electricity

27

generated, and depends on the date of

commissioning and the size of the plant. The

tariff rate varies by country.

Figure 36: Return on investment

28

6 Mounting System and Installation

The specific properties of each BIPV project,

such as location and application, along with

differing regulatory specifications for safety

and loading capacity of materials used,

combined with specifications on PV

installations within each country, will all have a

decisive impact on the BIPV technology or

panel specification employed along with the

chosen method of fixing/mounting the BIPV

panels.

The façade systems highlighted are by no

means the only solutions available, with many

clamping, bonding, and framing systems

available for all types of façade cladding.

Additionally, insulation considerations must be

taken into account as well as ducting for wiring

and connectors.

6.1 Linear Mounting

Systems

Polysolar work with several freely available

curtain walling and bonded glazing systems,

such as Nvelope, Technal, Kawneer, Comar,

SAPA, Reynaers, SAS, and Schüco. These

aluminium profiles require slight adaptations to

accommodate the wiring and connectors, but

standard products are used for both windows

and walls and can even be adapted for

opening windows.

6.1.1 Mullion-transom

façades

Mullion-transom constructions commonly

known as curtain walling, consist of vertical

mullions and horizontal transoms. The mullions

transfer the main loads and the transoms act

as horizontal bracing. The solar PV glazing

modules are set in this framework structure as

fill elements (either as a double-glazed unit or

single laminate). Clamping rails are fitted from

the outside as linear fixings for the modules with

capping over.

The circumferential profiles of the capping,

however, can shade the solar modules and

result in the accumulation of dirt and snow. The

costs for maintenance and cleaning should

also be taken into account if applicable,

particularly for roofing/skylight applications.

Additionally, the curtain walling capping

should be able to accommodate the wiring

and connectors. They can be internal or

external to the building. The gap in the

aluminium capping profile should be around

19 mm to accommodate MC4 connectors

and 11 mm for Phoenix Contact micro

connectors.

The dimensions of the façade grid will vary

from project to project and customised or fill in

“dummy” modules are sometimes required.

Mullion-and-transom façades count as

“warm” or thermally insulating façades.

Consequently, not only should the profiles be

thermally separated, but also the U-values of

the fill elements must be correspondingly low.

For this reason, PV modules can be integrated

in a thermal insulation glazing structure.

Curtain wall systems are a major consideration

in energy-efficient façade renovation projects

as well as new builds. Consideration should be

made that the system itself, whilst possibly

requiring additional initial funding, often pays

for itself within its lifetime and as such should be

regarded not as an additional expense but as

a lower lifetime cost option that can provide

the same functions and more.

Polysolar works with most commercially

available curtain walling profiles, both for

facades and overhead glazing, usually

requiring only minor adaptations to

accommodate the PV cabling in the design.

Figure 37: Installation of Polysolar transparent modules

29

6.1.2 Structural sealant

glazing (SSG)

With structural sealant glazing façades, the

solar modules are fixed in place on a metal

frame by means of circumferential load-

transferring bonds. This bonding process is no

different from standard structural facades.

This produces façades or overhead structures

with a homogeneous and smooth

appearance. Furthermore, SSG façades have

no external protruding parts, ensuring shading

and dirt traps are avoided.

These façades tend to be mainly deployed as

bonded rainscreen cladding, using aluminium

back bars, and specialist glass glues, but

bonding can equally be used in other

applications and materials.

A layer of air between the load-bearing wall

(or the insulation layer attached to it) and the

building envelope ventilates the solar modules

from the rear and can be used for laying

electrical components and connectors.

Many different types of material, such as

plaster, ceramic tiles, bricks, glass or metal can

be used for this kind of construction. Façades

can thus be created using a wide variety of

material combinations together with PV

modules or as modules alone. Additionally, LED

lighting and imaging can be incorporated into

translucent facades.

In some countries, regulations require

additional mechanical safeguards to prevent

panels installed above a height from falling. In

addition, provision for the mechanical transfer

of loads must be made.

6.2 Point-Fixing

systems

Particularly delicate designs can be achieved

using point-fixed façade systems. Typical

point-fixing systems are clamp fixings and

undercut anchor-fixing systems.

Mullion Transom Façade Structural Sealant Glazing

Mullion Transom Façade Structural Sealant Glazing

Figure 38: Linear mounting systems

Figure 39: Ventilated rainscreen cladding system and fixing

30

Although point-fixing systems cause hardly any

shading in comparison to framed systems and

are less prone to accumulating dirt, they can

only be used with certain types of solar module

or in certain applications.

6.2.1 Drilled spot fitting

Drilling in glass tends not to be possible as this

affects the semiconductor layer. Standard

thin-film modules are generally not suitable for

drilled spot fixing unless specified prior to

manufacture.

6.2.2 Clamp fixings

Clamp fixings are used in conventional PV

panel installations, where the modules are pre-

framed. In thin-film PV panels they are also

used with rubber brackets to provide support

and allow thermal expansion.

U-shaped brackets that fit around the edge of

glass panes dispense with the need to drill

holes in the glass. The fixings must overlap the

glass by at least 10 mm and the clamped area

must be greater than 1000 mm2. Depending

on application, loadings and size of panels,

fewer or greater number of clamp points or

continuous edge clamps are required to avoid

edge stress on the glass.

6.2.3 Undercut anchor

fixings

Undercut anchor fixings are mechanical point-

fixings that remain invisible, since the glass is

not drilled right through. This allows more

efficient use of the PV surface area. These

fixings generate higher stresses due the

reduced contact area of their cylindroconical

drilled holes, which means that toughened

glass, semi-tempered glass or laminated safety

glass must be used.

6.3 Installation

Situations

The demands made on BIPV systems vary

according to the type of fixing system and

installation situation. The rules governing

system installations vary by country and note

should be taken of the local regulations

applying. This report covers British guidelines

only.

Drilled spot fitting

Drilled spot fitting Clamp fixings

Clamp fixings

Undercut anchor fixings

Undercut anchor fixing system

Figure 40: Different Point Fixing systems

31

6.3.1 Sloping glazing

The orientation of glazing with respect to the

vertical affects the loads on the glass. The

effect of gravity means that glass on a slope is

more likely than vertical glass to fall from its

fixings following breakage. Sloping glazing is

defined in BS 5516 as glazing that makes an

angle of 15° or more with the vertical. Glazing

that makes an angle of less than 15° to the

vertical will still be subject to some out-of-plane

load that will tend to pull it from its fixings.

Sloping BIPV glazing commonly occurs on

roofs, skylights or canopies of glazed buildings,

but it may also arise in sloping walls of glazed

buildings.

Solar modules installed at an angle greater

than 15° are classified as overhead units and

must comply with specified requirements. As a

rule, laminated safety glass with a PVB

intermediate film should be used as standard.

Solar modules that have cells within the

intermediate film or have an intermediate film

made of EVA do not necessarily meet

regulations.

For roofing, canopy and skylight applications

Polysolar has developed several bespoke

mounting systems as well as using off the shelf

solutions from other manufacturers.

For roofing applications, there is a distinction

between Building Integrated (BIPV) and

Building Applied (BAPV), with the latter being

placed on a building without performing a

secondary function other than power

generation, requiring some other form of

weather proofing to the roof. ‘In Roof’ PV

mounting also falls into this category.

BIPV roof mounting systems also include:

• Plastic buckets flush mounting

These comprise plastic trays which

deliver the weather protection to the

roof while holding the PV panels flush

to the roof-line. Companies such as

GTE or specialist systems for new build

homes. These systems can take both

framed and unframed modules but

are unsuitable for transparent

modules.

• Clamps

Clamps are standard for mounting

BAPV but can also be used with

unframed glass laminate panels, with

roof sealing through an under-felt or

mastic glue. Glass clamps are often

suitable for canopies or carparks

where guaranteed water tightness is

not essential. A range of suitable glass

clamps can be acquired from

Polysolar or conventional glass

companies.

• Sealed framed aluminium mounting

systems

When assured water tightness is

required, such as a domestic dwelling

roof, a sealed edge framework is

necessary to mount the panels. These

can be either transparent or opaque

with back insulation. GB-sol and others

offer a suitable system for Polysolar

glass.

• Tiled framed mounting panels

As an alternative to the heavy

framework of the sealed aluminium

frame, an overlapping tile

arrangement is also available on

which to mount the panels. These

systems have a gasket and aluminium

frame around each panel to give a

low-profile roof. Supplied by

companies such as Schweitzer.

• Bonded unframed systems

Other systems are similar to bonded

rainscreen cladding with the panels

glued to a framework with a

waterproof underlay or mastic

sealants in canopies. Bonding can be

to metal, wood or composite

materials.

• Horizontal curtain walling

Like vertical curtain walling, aluminium

and PVB systems are available for

roofing applications, particularly for

skylights and conservatory/atria

roofing which have complete sealed

framed mounting systems.

Figure 41: Mounting panels

32

• Glazing bars

Conventional glazing bars are also

used to mount PV panels on roofs,

particularly in canopy arrangements.

These comprise an undermounting

bar, rubber gaskets with a top cap.

These can be self-supporting or

mounted on the rafters. Used with

glass laminate panels, Polysolar has

recently introduced a bespoke

glazing bar design from 123V PLC that

can span over 5 metres between

supports and has an integral conduit

for the wiring, in which to hide the

connectors.

6.3.2 Vertical glazing

Vertical glazing is defined in BS 5516 as glazing

that makes an angle of less than 15° with the

vertical. Glass at any angle to the vertical will

be subject to out-of-plane dead loads. It

commonly forms the walls, windows and

entrances of glazed buildings.

As described, BIPV can be mounted into

standard curtain walling, rainscreen cladding

and window systems. Vertical installation

applications significantly widen the scope for

PV in the urban environment making all

uprights potential power generating surfaces,

even if the energy yields are lower than a

pitched alternative.

6.3.3 Glass barriers

Barriers provide containment, this is the ability

of the glazing product to prevent persons who

accidentally fall against the glass from falling

through. Replacing conventional glass barriers

with PV panels provides a highly attractive

solution.

Three main types of barrier defined in BS 6180

use glass:

• Freestanding protective barrier

A barrier in which the glass performs all

the mechanical functions. There are

no posts; the glass is cantilevered from

the floor and often has a continuous

handrail mounted on the top edge.

Polysolar has recently introduced a

balustrade system with a floor

mounting and uninterrupted profile.

With transparent PV glazing gathering

light from both sides exterior

balustrades offer an attractive

alternative.

• Barrier with a glass infill

A barrier with a continuous handrail

and posts, which carry design loads,

and a glass pane underneath the

handrail that provides containment

but no structural support.

There are numerous off the shelf

component solutions for both

balustrades and fencing that contains

the glass. The glass and degree of

lamination can be varied for the

application such as road noise or

security barriers

• Full-height barrier

The glass forms part of or the whole of

a wall in a building. Again, there is a

range of glass available and coatings

to provide the desired look and

structure.

6.3.4 Walk-on glazing

Due to the type of use, walk-on glazing is at

greater risk of being damaged by knocks. Its

stability and fitness for use must be

demonstrated by means of structural analysis if

unfavourable loading conditions apply (1.5 kN

individual loading, 3.5 kN/m2 traffic loading).

Only laminated safety glass with at least three

layers should be used. The topmost layer

should be thicker than 10 mm and be made of

toughened or semi-tempered glass. The

bottom layers must be thicker than 10 mm and

be made of float glass or semi-tempered glass.

Figure 42: Freestanding protective barrier

33

6.3.5 Step-on glazing

Step-on glazing is usually only intended to

support loading during maintenance or

cleaning by one person at a time and must be

made of laminated safety glass panes with at

least two individual sheets.

If trafficked areas beneath step-on glazing are

not sealed off while the glazing is being walked

on, it is classified as overhead glazing.

Figure 43: Polysolar glazed roof

34

7 Electrical System In a PV array, several PV modules are usually

connected in a string to form the solar

generator. This solar generator generates a

direct current (DC), which is fed to an inverter

where the it is converted to alternating current

(AC). Provided it is not consumed or stored

directly on site, this electrical power is

registered via an electricity meter and fed into

the public supply grid. Within a large scale BIPV

project, most electricity produced will be used

on site.

7.1 Solar panel A photovoltaic module consists of several solar

cells interconnected within the module. The

way in which these internal connections are

made determines the relationship between

voltage and current and is usually limited by

process-related factors. Connecting the

individual cells in series increases the voltage,

while connecting them in parallel increases

the current generated by the module.

The electrical connection is usually made on

the rear side of the module via a connection

socket, which is normally fitted with a diode.

Edge sockets or connections on the front face

are also possible. To ensure easy and safe

installation, cables are used at the connection

sockets together with touch-proof plug

connectors that are protected against polarity

reversal.

7.2 Solar Array The solar array, or generator, is the name given

to the entire PV system, comprising all the solar

modules that are connected in a single

system. The type of connections between the

PV modules determines the cabling system,

the system stability and the necessary cable

dimensions. PV modules can be connected in

parallel or in series to form an array.

7.3 Connections As a rule, solar modules have two connection

cables with plug connectors that are

waterproof and protected against polarity

reversal. This makes it easy to connect the

different modules together. The requirements

to be met for PV module cabling are

significantly higher for direct current cables

than for alternating current cables, due to the

relevant safety regulations.

Cables for solar systems must be UV resistant,

protected against moisture and sufficiently

insulated. When determining the cross-section

of the cables that link the modules, possible

line losses in the system must be considered

and it must be ensured that the cables cannot

overheat.

The cable routing depends on the type of

façade or roof system. With rear-ventilated

façades, the connections and cables are

routed through the air gap. With mullion-

transom façades , and particularly if semi-

transparent modules are used, the cables are

often routed through the profiles of the

façade. In this case solar modules with edge

sockets can be used.

7.3.1 Serial connections When the solar modules are connected in

series, the voltage increases with each module

while the current remains constant. Since the

same current flows through all the series

connected modules, the same cable cross-

section can be used throughout.

7.3.2 Parallel connections When solar modules are connected in parallel,

the current increases with each module while

the voltage remains constant. This means that

the requirements for safe low voltage systems

can be met. On the other hand, larger cable

cross sections are required.

The interconnections for BIPV systems can be

complex due to the different orientations,

shading conditions, temperatures or even

output ratings of the individual modules. A BIPV

system should therefore be subdivided into

several segments with environmental

influences that are as similar as possible. The

smaller and more differentiated these

segments are, the more stably and efficiently

the installation will be able to run.

35

7.4 DC and AC load-

break switch The DC isolating circuit breaker allows all the

poles of the photovoltaic electricity array to be

switched off and is installed in the

interconnecting cables between the modules

and the inverter. Therefore, it is possible to

switch off the system on the direct current side,

for safety reasons.

7.5 Inverter The solar inverter converts the direct current

from the solar modules into grid-compatible

alternating current (frequency and voltage)

and thus forms the link between the PV

electricity generator and the public supply

grid.

Further important tasks carried out by this

component are the regulation and

optimisation of the output and the recording

of essential operating data.

Depending on their capacities, inverters can

be used as a central inverter for the entire

system, as array inverters for each module

array or as micro inverters for each individual

module. Inverters should be installed in

positions where they will remain as cool and

well ventilated and protected as possible. As

already mentioned, BIPV systems should be

divided into several segments or subsystems

with the same environmental influences and

output capacities. This means that centralised

inverter concepts are not usually possible. The

inverter must be selected, first and foremost, to

suit the optimum segment sizes, so that each

part of the systems has its own Maximum Power

Point (MPP) tracker. This MPP tracker ensures

that the solar array always operates within an

optimised output range.

In contrast to purely yield-optimised systems

with optimal environmental variables, the

inverters of a BIPV system that rarely operates

in maximum direct sunlight and is not optimally

aligned can often be scaled down or the

maximum module output assigned to the

inverter can be significantly exceeded.

7.6 AC load-break

switch The AC isolating circuit breaker allows all the

AC poles of the inverter to be switched off and

is installed in the interconnecting cables

between the inverter and the generation

meter. Therefore, it is possible to switch off the

system on the alternate current side, for safety

reasons.

7.7 Generation meter A generation meter is required if the solar

electricity is to be fed into the premises or grid.

In principle, this meter performs the same

function as a standard electricity consumption

meter, except that it measures the electricity

that is generated instead of the purchased

electricity. The meter readings are used to

calculate the payment received, on the basis

of Feed-in-Tariff (UK) or alternative systems

operating in different countries. Smart meters

are required to measure the amount of

electricity fed back into the grid rather than

used directly within the premise. The

connection of the solar plant to the public grid

must be carried out by a qualified electrical

specialist (MCS certified in the UK) and agreed

by the electricity supply company.

Grid connected PV systems can feed in either

all the generated electricity or just the excess

electricity that is not required on site.

Consequently, the plant operator can decide,

according to his requirements, whether to

store the generated electricity in batteries, use

the electricity directly or sell it to the electricity

supplier.

Net PV plants that have no connection to the

public grid are referred to as autonomous off-

grid PV plants or island systems, where all the

electricity generated is used by the plant

owner. As a rule, intermediate storage of the

solar electricity using batteries is necessary.

PV plants that are combined with other

systems for energy conversion are referred to

as hybrid systems. Wind power plants, diesel

generators, biogas plants, fuel cells or micro

hydro plants are typical systems.

36

Figure 44: Solar PV Diagram

37

Polysolar looks forward to receiving comments

and suggestions on this publication, which we

hope you will find useful as a tool to designing

with PV. Polysolar would be pleased to help

you with any questions or design requirements

regarding your BIPV projects.

It should be noted that these guidelines do not

refer to UK MCS specifications and are not

specific to any one manufacturers’ products.

Specific advice should be sought from the

manufacturer or certified installer before

commencing with a BIPV project.

Published by;

Polysolar Ltd

Hauser Forum

Charles Babbage Road

Cambridge

CB3 0GT

United Kingdom

Tel: +44 (0)1223 911534

iInfo@polysolar.co.uk

www.polysolar.co.uk

Replication permissible with the written permission of

Polysolar. We acknowledge the assistance of

Odersun AG in the production of this publication.

Figure 45: Curtain wall structure