Post on 20-Oct-2015
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
16 renewable energy focus Green Building supplement November/December 2008
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.
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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.
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BIPV
18 renewable energy focus Green Building supplement November/December 2008
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)
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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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