BIPV Built-In Solar Energy

Feature article

14 renewable energy focus Green Building supplement November/December 2008

BIPV: Built-in solar energyIN A TIME WHEN SOLAR PV IS CHARACTERISED AS BEING A

PROHIBITIVELY EXPENSIVE ALTERNATIVE FORM OF ENERGY SUBSIDIES

NOTWITHSTANDING, ONE APPLICATION AREA THAT COULD MAKE

A REAL DIFFERENCE TO PERCEPTIONS IS BUILDING INTEGRATED

PHOTOVOLTAICS BIPV. AND SUCH SYSTEMS HAVE NOT ONLY BECOME

MORE EFFICIENT, BUT ALSO MORE ATTRACTIVE AND ADAPTABLE. Andreas Henemann

In the past, having solar panels on the roof of your home was the prerog-

ative of the eco-warrior. The modules may have meant that you were

producing energy cleanly from a renewable source, but it was also a social

and political statement. The solar panels were obtrusive, did not fi t in

harmoniously with any home design and long discussions between

spouses preceded any decision.

However, R&D in photovoltaics has led to enormous steps forward. And the

outcome is Building Integrated Photovoltaics (BIPV), a method by which

the PV modules can be incorporated into the external fabric of the

building.

BIPV is growing in popularity as more and more architects and

constructors begin to understand the possibilities available to their

clients. The incentive structures in specific markets can also make

larger-scale PV development attractive to both building owners –

who can offset electricity costs/generate money through feed-in-

tariffs (FiTs) by investing in their roof space – as well as equity

investors who see the opportunity to make money from large scale

BIPV projects.

Various current initiatives in Europe off er high levels of subsidies for BIPV, or

seek to mandate the construction industry to integrate more renewables in

buildings, eff ectively a green light for BIPV. And the USA could also become

an improved market with the recent announcement of an eight-year Invest-

ment Tax Credit (ITC) for solar initiatives. Even in markets where incentive

schemes don’t tend to favour PV, BIPV can help building owners save on

their electricity costs.

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BIPV


BIPV seeks to create as much function as possible from the building space.

One example is the PV solar facade; these can in many cases be cheaper to

construct than normal building facades (not to mention able to generate

electricity), and the appearance can be attractive and modern, something

that overcomes a key barrier to PV takeup in the eyes of some potential

customers.

BIPV could be a transformational technology, slashing the high propor-

tion of conventional energy consumption accounted for by buildings,

cutting CO2 emissions and easing pressure on fuel reserves. But further

progress requires a high level of innovation to truly bring solar PV into

buildings, and make the technology aff ordable.

What is BIPV?

Essentially, BIPV refers to photovoltaic cells which can be integrated into

the building envelope as part of the building structure, and therefore can

replace conventional building materials, rather than being installed after-

wards. Rather than sticking out like a sore thumb, BIPV modules can be

naturally blended into the design of the building, creating a harmonious

architecture. The beauty of BIPV lies in the name: it can be used in any

external building surface. According to Udo Möhrstedt, the ceo and founder

of IBC SOLAR, “BIPV represents great contemporary, innovative potential,

an excellent way for the buildings of the future to be truly ‘green’.”

Why BIPV?

At fi rst glance the most distinctive attribute of BIPV is its appearance.

Until now, PV has been a compromise between energy and aesthetics, as

despite being effi cient energy providers, the modules were not always

pleasing to the eye. However, BIPV modules can be colourful and visually

arresting. Using BIPV creates a strikingly futuristic building. Its fl exibility is

such that it can respond to the architect’s imagination and result in a

building that is both impressive and environmentally friendly. It improves

the image of a building and increases the resale value.

BIPV systems can either be connected to the available utility grid or

designed as stand-alone, off -grid systems. Buildings that produce power

using renewable energy sources decrease the demands on traditional

energy generators, reducing the overall emission of climate-change gases.

And the consumer can makes savings through lower electricity bills – due

to peak shaving (matching peak production to periods of peak demand).

Other advantages include:

Photovoltaic modules can be integrated into the building envelope in

a so-called “non-ventilated facade”, both on public buildings such as

offi ce complexes, production buildings, shopping centres or schools,

and on private buildings such as indoor gardens or terraced houses.

The modules replace traditional building materials (e.g. spandrel glass)

in new build and create an ambient inside temperature all-year

round;

“Ventilated facades” can be installed on existing buildings, giving old

buildings a whole new look. These modules are mounted on the

façade of the building, over the existing structure, which can increase

the appeal of the building and its resale value;

Solar modules can be incorporated into saw-tooth designs and

awnings on a building façade. The angle of the awning increases

access to direct sunlight, meaning increased energy. These can be

used in entrances, terraces or simply as awnings to shade the rooms

inside;

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Commercial BIPV technologies

Today, mono and polycrystalline forms of silicon are the mainstay of

the solar PV array industry. One strand of innovation is to incorporate

these materials into modules that double as building elements, tiles and

shingles in particular.

While crystalline silicon remains the dominant building PV technology, its

position is being challenged by thin-fi lm alternatives. Thin-fi lm solar

materials that can conform to the building envelope can potentially

supplant the rigid ‘add-on’ arrays that adorn buildings today. Initially this

trend is based on the exploitation of amorphous (non-crystalline) and

micromorphous forms of silicon. The ability to deposit such material

extremely thinly onto suitable substrate materials can yield solar cell

wafers many times thinner than those produced from conventional

crystalline silicon, which cannot be sliced from ingots to anything like the

same degree of fi neness.

Thin solar materials not only maximise the amount of active surface area

exposed to solar radiation for a given volume of silicon, they also lend

themselves to integration with buildings because they can be made

fl exible and readily-bondable to the surfaces of conventional materials.

Some are thin enough to be incorporated into glass while retaining

transparency, eff ectively freeing solar PV from the confi nes of the roof

and bringing it into facades.

Producing thin-fi lm materials in continuous roll-to-roll processes – rather than

the batch step-and-repeat processes associated with conventional crystalline

silicon – off ers the prospect of cost-effi cient production and reduced system

cost per installed power capacity. Producers can leverage innovations in

large-area deposition, roll coating and other processes used in the fl at panel

display and architectural glass industries. Using amorphous silicon (a-Si or

ASI) has the added advantage of sidestepping diffi culties currently faced by

manufacturers regarding the global shortage of crystalline silicon wafers.


BIPV

renewable energy focus Green Building supplement November/December 2008 17

Using photovoltaics in a building envelope replaces traditional building

materials and building processes. For example using BIPV in roofi ng

systems may replace batten and seam metal roofi ng, and traditional

3-tab asphalt shingles;

Glass-glass modules can be utilised as balustrades on balconies, for

example for large rented accommodation or terraced houses, creating

an eye-catching structure;

Using photovoltaic cells for skylight systems in entrance halls, atria or

courtyards, can be both an economical use of solar energy and an

exciting design feature. BIPV cells have the advantage that their trans-

parency can be varied so that if desired, the module can provide

shade or be semi-transparent;

Modules protect against the weather, giving shade from the sun as

well as protection from wind and rain. They also protect against light-

ning, being an electrical resistor;

When the weather gets cold (or hot) non-ventilated modules act

as thermal insulation through the sandwich-construction of the

modules themselves, the layer of air within the modules and the

ray absorption by the crystalline silicon and thin film solar cells.

This means that less energy is wasted by heat loss from the inte-

rior, reducing heating costs and keeping the building at an ambient

temperature;

Equally, the cells repel unwanted noise pollution and create a

screen against potential electromagnetic interference, including

so-called electro-smog. This makes them particularly useful in situ-

ations with large amounts of sensitive electrical activity, for

example hospitals or airports.

Technologies for BIPV

The technology a building owner would need to select for BIPV depends

on factors related to the roof’s location. For example, crystalline modules

would be recommended for scenarios where the building in question has a

southern orientation (plus or minus 45%), with an inclination of between 20

and 60 degrees.

However, on other projects with less than optimal positioning – for

example premises that have fl at roofs, industrial roofs, semi-fl at roofs, or

east/west facing roofs and façades (to name a few examples), thin fi lm

technology could be an eff ective solution to maximise power output

available while off setting the capital investment of installation. Thin fi lm

solutions also tend to be used on large roofs and industrial premises

where space and area isn’t a problem. As a general rule of thumb, thin

fi lm technologies need roughly double the amount of area of modules

for the same kW output.

Another current challenge for the BIPV industry is to combine the latest

module technologies with the best roofi ng materials to develop/create a

new solar system – such as solar roofi ng systems that utilise roofi ng

membranes with cables on the underside, for example.

Current BIPV policy

Both business and Government are aware of the need to change how we

look at the buildings around us. Technological innovation has paved the

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way for the adoption of solar systems, and we have fi nally reached the

situation that The European Charter for Solar Energy in Architecture

and Urban Planning called for in 1996:

“The aim of our work in the future must […] be to design buildings and

urban spaces in such a way that natural resources will be conserved and

renewable forms of energy − especially solar energy − will be used as exten-

sively as possible. […] In order to attain these goals, it will be necessary to

modify existing courses of instruction and training, as well as energy supply

systems, funding and distribution models, standards, statutory regulations

and laws in accordance with the new objectives. […] New systems and prod-

ucts in the fi eld of energy and construction technology should be capable of

simple integration into a building and should be easy to replace or renew”

– (Norman Foster, Frei Otto et al., Solar Energy in Architecture and Urban Plan-

ning. Prestel Verlag, München, New York 1996).

It is with ideas such as these in mind that public bodies look favourably on

photovoltaics. BIPV is currently one of the fastest-growing areas of the photo-

voltaic industry. BIPV improves the energy use of a building and can generate

income through compensation for electricity fed into the grid.

In France, as of 2008, general feed-in-tariff s for non-integrated solutions come

to 31.193 €ct/kWh on the mainland and 41.591 €ct/kWh in the DOM-TOM

and Corsica. Building integrated feed-in-tariff s are higher at 57.187 €ct/kWh

on the mainland, and 57.187 €ct/kWh in the DOM TOM and Corsica. The

In the Netherlands, IBC SOLAR was involved with the installation of a ventilated façade – this

incorporated 108 5.8 kWp of Kaneka 54 modules onto a production building, creating a

visually-arresting working environment.


BIPV


Future BIPV technologies – the organic connection

Progress in organic PV continues to accelerate.

These solar cells made from plastics show great promise for decreasing

the cost of solar energy to the point where they are expected to become

widespread in the decades ahead; they will cover skyscraper façades and

car roofs, or even be a part of clothes.

The traditional silicone-based PV used today are expensive, as the

price of crystalline silicone is rising due to high demand for computer

chips. As this need is not likely to decrease, the prospect of a cheaper

alternative which comes in a flexible and light film – and that could

even be sprayed or printed onto a surface – attracts the interest of

many universities, national laboratories and several companies around

the world. Organic photovoltaic cells (OPV) are solar cells made

mostly of organic molecules. Polymer OPV devices are typically made

by solution-processing blends of two conjugated polymers, or a

conjugated polymer with a molecular sensitiser. The most common

materials are PPV – Poly(p-phenylene vinylene), polyfluorenes, or

polythiophenes. Polymer or plastic solar cells are the most heavily

researched of all OPV technologies because they are the most

promising when it comes to low cost.

However, researchers predict that the day when buildings are energy

self-sufficient due to organic PV is still far away. While great progress

has been made towards understanding the chemistry, physics, and

material science of polymer organic PV, more work is needed to

improve their performance. Organic photovoltaic cells have not yet

been developed to attain the same conversion rate (how much of the

sun’s energy is converted into electricity) as traditional PV cells, which

achieve around 15%. PlasticsEurope – the European Association of

Plastics Manufacturers – confirms that further research is needed to

bring plastic solar cells to the market. But the prospects look very

exciting, especially with the mounting investment put into this

technology.

There is one European country in particular which seems to be

positioning itself as a future market leader. In July 2007, the German

Federal Government announced its support for industrial partners

working on organic PV with €60 million – within the framework of its

High-Tech Strategy. Companies such as BASF, Bosch, Merck and

Schott are working together at full steam – planning to spend up to

€300 million out of their own budgets – to achieve mass-producible

plastic PV membranes which can be curved, rolled and bent around

corners.

All eyes on conversion and lifespan

In 2004, scientists at Princeton University produced organic photo-

voltaics of improved efficiency by stacking two types of organic cells

in a series. The absorption of light was maximised by tuning one type

of cell to absorb long-wavelength light, and another to preferentially

absorb short-wavelength solar energy. They achieved a maximum

power conversion efficiency of 5.7%. At the time, they suggested that

power conversion efficiencies exceeding 6.5% could be obtained

through this technique.

They were right. In 2007, a team of Korean and North American

researchers announced the solar cell they had created had an

efficiency of 6.5%, and could even make use of infra-red. This was

achieved by again placing one cell on top of the other but using

nano titanium oxide in between. The upper layer absorbs luminous

light, while the lower layer makes use of infrared. At the time,

scientists predicted that by using a special encapsulation process, the

lifespan of their plastic-based solar cell could be extended consider-

ably, overcoming the lifetime problems of most organic photovoltaics

to date. This two-layer cell is expected to achieve low manufacturing

costs by adopting a form of spin coating (the same spin coating that

German BASF is working on – see above).

Lifetime problems could very soon be a thing of the past. In June

2008, the Energy Research Centre of the Netherlands (ECN)

announced that an organic PV material called PowerPlastic – designed

by Konarka Technologies, Inc. demonstrated outstanding long-life

capabilities after comprehensive environmental testing under

accelerated conditions, including high temperature storage and

prolonged illumination. This technology (contrary to the belief of

many researchers that organic solar cells require packaging with

either glass or very expensive ‘super barriers’) has demonstrated an

outstanding lifetime for flexible cells packaged with commercially-

available, low-cost materials.

In four years, Konarka says it intends to have products for the building-

integrated photovoltaics market with “bifacial cells,” for placement on

windows, which can convert electricity from both sides. And according to

the Joint Innovation Lab – Organic Electronics in Germany, fold-up

chargers for laptops or mobile phones are right on the brink of large-

scale production. Plastics technology is well positioned to take on the

energy challenge, and the industry is sure that the world’s perspective on

energy will change dramatically once plastic-based photovoltaics gains

mass-market momentum.

Jan-Erik Johansson – Regional Director North of PlasticsEurope – the

European Association of Plastics Manufacturers.

A glass substrate is spin-coated. This involves coating the substrate with a material fi lm,

which is only a few nanometres thin, suitable for use in the colour solar cell. The previously

sprayed substrate is placed on an aluminum plate and coated with the prepared solution.

The plate is rotated at up to 6000 revs/minute to ensure that the solution is evenly distributed

on the substrate (Source: BASF)

Film of fl exible organic photovoltaics (Source: Konarka)


BIPV

renewable energy focus Green Building supplement November/December 2008 19

contracts have a duration of 20 years and are linked to infl ation. Additional

investment subsidies are available as tax credits.

On the other side of the Atlantic, in the USA, fi nancial incentives are organ-

ised at both State and Federal level – Federal tax credits of 30% are on off er,

capped at US$2000 for residential systems, but with no cap for businesses. A

new 8-year ITC has just been passed by the US Congress.

In Germany, the legal framework is the German Renewable Energy Sources

Act (Erneuerbare-Energien-Gesetz – EEG). Under this, the feed-in-tariff s for

BIPV from 2009 will go from 43.01 €ct/kWh for a system of less than 30 kWp,

to 40.91 €ct/kWh for a system between 30 and 100 kWp, to

39.58 €ct/kWh for a system of more than 100 kWp. Contracts last for 20 years,

during which time there is constant remuneration.

The German law was one of the fi rst to come into force and since then

similar models have developed all over the world. In Asia, Malaysia intro-

duced the Renewable Energy Power Purchase Agreement (REPPA) in

2001. The REPPA allows independent power producers to sell electricity to

the grid. The selling price for electricity for renewable sources was capped

at a ceiling of RM17 cent/kWh or US$0.045/kWh. To date, more than 60

project proposals have been approved by the Special Committee on

Renewable Energy (SCORE) chaired by the Ministry of Energy Communi-

cations and Multimedia.

Legislation like this has permitted corporations such as IBC SOLAR to

undertake projects all around the world. In Pusat Tenaga in Malaysia, IBC

SOLAR completed a BIPV project integrating PV into the roof of an offi ce

complex. Dubbed the “Zero Energy Offi ce”, the building is self-suffi cient,

with enough power from solar systems for the targeted building energy

index of less than 50 kWh/m²/year (4200 m² fl oor area, accommodating

up to 111 staff ). There are four diff erent PV systems installed in the

building, demonstrating the diff erent ways external surfaces can be used

to harness solar energy.

The fi rst and biggest comprises of 47.28 kWp polycrystalline modules on

the main roof, followed by amorphous silicon modules with a capacity of

6.08 kWp on the second main roof. The building atrium is made of glass-

glass semi-transparent modules with a capacity of 11.64 kWp. The use of

solar modules is not limited to the offi ces as the car park roof is inte-

grated with monocrystalline modules with a capacity of 27 kWp.

Looking to the future

In the future many more demands will be made of building envelopes.

They will not be merely required to shelter us from the weather, but they

will also need to meet the exacting requirements of the architects,

building designers, building owners and even buildings users.

Greater requirements for comfort (concerning light and temperature

inside the building);

Greater requirements for heat insulation and energy saving – buildings

will have the goal of equalising the energy input with the energy

output;

Protecting building users from negative environmental impact (e.g.

pollution, noise and smells);

Passive, environmentally friendly and noiseless solar energy use.

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As stated in The European Charter for Solar Energy in Architecture and

Urban Planning, it will “be necessary to modify existing courses of instruction

and training, as well as energy supply systems, funding and distribution

models, standards, statutory regulations and laws in accordance with the

new objectives.” (Norman Foster, Frei Otto et al., Solar Energy in Architecture and

Urban Planning. Prestel Verlag, München, New York 1996)

The future “green buildings” will look very diff erent to the landscape we see

around us today. BIPV responds to these needs by providing energy to the

utility grid as well as reducing the reliance on the grid. Furthermore, due to

the insulation benefi ts of solar modules, it reduces energy wastage. The new

buildings of today also represent a long-term investment in the future. The

buildings we erect now will still be standing in 2050 and so we must be

aware of the implications this has; they will defi ne our future living and

building environment.

Norbert Hahn, vice president marketing & sales at IBC SOLAR foresees a

growing interest in photovoltaics: “Thinking mid- to long-term, we anticipate

a strong demand for BIPV from abroad for new build − from Asia and the

United Arab Emirates in particular. We anticipate increased call for BIPV, both

in Germany and in Europe as a whole, in the restoration of existing building

stock. This is because of new carbon dioxide reduction targets, which building

regulations play a crucial part in.”

Despite currently being a young innovation, in the future BIPV needs to be

standardised in order to allow the mass production of modules, and the ease

of purchase and replacement. However, this standardisation must not inhibit

the creativity of the architect. BIPV modules should be constructed to allow

a gradual replacement of any traditional building material.

Above all, it is essential that there be close working relationships between

architects, planners and industry – through an exchange of information

and training so that the full potential of BIPV may be exploited. With BIPV,

solar systems are becoming a standard building component, just like

glass panes or doors. This allows homeowners and architects to take

energy consumption into account when designing a home, without

compromising energy effi ciency or aesthetics.

About the author:

Andreas Henemann is project manager of Building Integrated Photovoltaics, IBC SOLAR

it is essential [for a] close

working relationship

between architects, planners

and industry...so that the

full potential of BIPV may be

exploited.


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BIPV Built-In Solar Energy