Photo 1: PV-Cladding, 4,2kWp, Ökotech 3, Berlin
Photo 2: Semitransparent cold facade with PV, 8,5kWp,
Greenpeace, Hamburg
Building Integrated Photovoltaics
New Developments and Trends in Europe
Ingo B. Hagemann, Architect
Architekturbüro Hagemann, Annuntiatenbach 43, D-52062 Aachen, Germany
Phone: +49/(0)241/34530, Fax: +49/(0)241/30547
E-mail: Ingo.Hagemann@RWTH-Aachen.de
Abstract – Photovoltaic technology (PV) is today a popular part of the building vocabulary. It can be used on both existing and new buildings. Its use in the building envelope is very varied and open ways for creative designers. In particular semitransparent photovoltaic glass modules can be changed into a truly multifunctional building component which is able to serve in addition to an electricity production other functions of the building envelope as well. Such synergy effects of a photovoltaic module only turn out to be successful if its integration in the building fabric is carefully understood and the photovoltaic is fully integrated into the overall design and energy concept of a building. Presently in particular non-technical barriers still need to be solved to allow an intelligent and wide spread application of photovoltaic in the built environment.
There is an increasing awareness about the destruction of the natural
environment and a growing concern about the quality of the built environment in
Europe. As a result goals, specifications and requirements for the construction
and design of buildings do change. In the center of interest of necessary
changes is the building envelope. The rise of new technological developments
allow today completely different visions of a conventional facade or roof. With
respect to the multi-functionalism of the building envelope it is more and more
necessary to make use of different active and passive solar techniques. One
solar technique, which is increasingly becoming an important part of the
building vocabulary, is the photovoltaic (=PV).
A photovoltaic module is basically a covering material which
has the added value that given the right conditions it can produce electricity
during certain periods of the day. The production of electricity may be
considered thus a bonus to this unique exterior building material. On the other
hand there is also a clear vision, that photovoltaic will be able to contribute substantially to
the main stream power production, even though it is still five times more
expensive than grid power [1]. Building integrated photovoltaic (BIPV) offers
cost advantages and is attractive for urbanized regions in countries, like the
Netherlands or Germany with not sufficient unoccupied land available.
Photovoltaic is used today in different ways on both existing and new buildings.
It´s use on facade and roof areas are very varied and open ways for creative
designers.
Facades occupy the
majority of the surface area of the structural shell of the building. A facade
gives each visitor an initial visual impression of the building and architects
are keen in using a facade to express their concepts and translate their
client´s whishes into an appropriate language of shape and color. As such,
standard photovoltaic modules can be added on the existing wall to provide an aesthetically
successful facade. The photovoltaic modules are just added on to the structure
and there is no need to provide a weather tight barrier, this being performed
by the structure underneath the modules.
Photovoltaic systems
can also be an integral part of the building element of the facade. The main
features of a photovoltaic laminate used as a cladding material are basically
the same as tinted glass. Photovoltaic laminates provide long lasting weather
protection, they can be tailor-made at any size, shape, pattern and color and
they can give partial lighting inside the building. They can be configured as a
simple facade plate or as a multifunctional element for cold or warm facades,
sunshading devices or as windows within the outer skin of the building. In
Germany these multifunctional photovoltaic facade elements are available from different
companies and can be assembled with standard mounting systems which are adapted
to this particular purpose.
The Ökotech 3 building
in Berlin [Photo1] is an interesting example of the added value of a photovoltaic facade.
The building´s facades consist of granite and glass panels using a star-shaped
mounting device (SJ-Facade-System) to fix the panels. The parapet area of the 2nd
to the 5th flour are covered with photovoltaic panels which are partially reflective, having
the same appearance as other glass panels. The use of expensive cladding
material gives the building a certain class. Using photovoltaic material shows that the environmentally
conscious owner is also producing part of his energy.
Photo 1: PV-Cladding, 4,2kWp, Ökotech 3, Berlin
Photo 2: Semitransparent cold facade with PV, 8,5kWp,
Greenpeace, Hamburg
As windows, photovoltaic laminates
can realize its transparency function in two ways. The photovoltaic cell itself can be so thin or laser grooved
that it is possible to see through it providing a 20-50% filtered vision to the
exterior. Semitransparent amorphous silicon modules are especially appropriate
for this but have not yet used much for building integration in Germany.
Crystalline cell
modules on the other hand may have the cells on the laminate spaced in such a
way that partial lighting filters through the photovoltaic element and illuminates the room. This is now
realized by different manufactures which are selling standard or custom made
see-through laminates. Light effects from these panels lead to an ever changing
pattern of shades in the building itself (Photo 2). The room remains shaded yet
not constrained. By adding layers of glass to the base unit of the
semitransparent photovoltaic module thermal and acoustic insulation as well
as other special requirements can be designed according to individual
requirements of each application (Photo 3). This type of a truly
multifunctional building component with photovoltaic is most successful in Germany and is able to
serve a large market in the building sector.
There is a growing
need for carefully designed shading systems on the building market due to an
increasing use of large window openings and curtain walls in today’s
architecture. Photovoltaic modules
of different shapes can be used as shading elements above windows or as part of
a roof structure. Since many buildings already provide some sort of structure
to shade windows, the use of photovoltaic shades should not involve any additional load
for the building structure. The exploitation of this synergy effect helps to
reduce the total costs of such a photovoltaic installation and to create added values to the
photovoltaic
as well as to the building and its shading system (Photo 4). New market opportunities
for photovoltaic could be developed if a mass production of photovoltaic shading elements could be achieved [2]. Photovoltaic shading
systems may additionally use one way trackers to tilt the photovoltaic array for
maximum power and at the same time provide a variable degree of shading.
Photo
3: PV-Facade with insulating glass, 4,5kWp, Tobias Grau
KG, Hamburg
Photo 4: PV-Shading system, 1,5kWp, Metal Company Lehr,
Mainz
Roofs are ideally
suited for photovoltaic integration. There is usually less shadowing effects at roof heights
than at ground level and a roof usually provides a large unused surface for
integration. For photovoltaic integration purpose, a distinction between
pitched and flat roofs is made.
An ideal pitched roof
for photovoltaic integration must be tilted towards the south (northern hemisphere) at
an angle of ±15° latitude for best power production. Roofs which are looking
towards the south east or south west are also acceptable and my even be of
advantage depending on the power requirement of the building. Photovoltaic modules
can simply be fixed on top of pitched roofs providing that special care is
given so that the integrity of the roof´s protection is not broken. This by
itself is not a true architectural integration of the photovoltaic element but is permits the installation of photovoltaic modules
easily on existing buildings. This type of low-cost application is still used
most to mount smaller photovoltaic systems (approx. 5 kWp) on on existing roofs
and private homes.
A more elegant way to
integrate photovoltaic is to use PV-Shingles or PV-Tiles which permits the mounting of the photovoltaic module
like any shingle or tile by a roofing contractor. Successful developments from
Germany are the “Braas Solar Roof Tile” (Photo 5) or the “Laumans Solar Roof
Tile”. Both are available on the market.
Flat roofs have the advantage of good
accessibility and ease of installation. The classical way of integration has
been to mount the array on a substructure which is then fixed to the roof. As
with pitched roof, special care must be given to fix the array without breaking
the integrity of the roof. Additional care must also be given to the added
weight of the array on the roof and against uplifting force of the wind which
could blow the modules away. Experiments and developments in this field have
lead to lighter, easier and quicker to handle standard array structures, such
as SOFREL®, SOLBAC® or the PV-ConSole®. In
addition to such standard mounting systems still a number of custom made flat
roof structures are carried out (Photo 7).
Skylights structures
are usually the best from a solar point of view since they can combine the
advantage of light diffusion in the building while providing an unobstructed
surface for the installation of photovoltaic modules of laminates. The photovoltaic elements
thus provide both electricity and light to the building. The photovoltaic modules
and support structures used for this type of application are similar to those
of semitransparent glass facades. These structure, which may appear rather
unpretending from the outside, produces fascinating light hallway walks and
floors and allow a stimulating architectural design of light and shadow (Photo
6).
Photo 5: Example of “Braas
Solar Roof Tile”, 1,4kWp, Alzenau
Photo 6: PV-Rooflight,
4,0kWp, Local Utility, Halle
The integration
aspects of Photovoltaic elements needs to be fully understood and researched.
It cannot suffice to simply replace existing building elements by those which
additionally incorporate photovoltaic elements. Its integration must always be
planned in the context of the building as a whole. An overall energy scheme
must be developed for the building right at the beginning of the construction
project, when the building size, shape and orientation are being made. The
chance of having any influence on the future energy demands of the building decrease
with every step of the planning. Additionally, efforts to make any structural
changes to the building increases as the project takes form. The higher the
degree of synergy which can be achieved between the photovoltaic material and its electricity production, the
more cost-effective will be its integration [3].
Most buildings which
were carried out so far does not provide massive cost savings or do show cheap
approaches of utilizing photovoltaic. As an energy source, photovoltaic is still expensive compared to other grid
energy sources. At the same time photovoltaic and its different applications are in a rapid
process of development and its cost. In Germany a number of efforts are
undertaken to foster the acceptance and demand of building integrated photovoltaic. The goal
is to reach a mass production of photovoltaic. Steps in this direction are:
The new government
buildings in Berlin, Germany, serve as shining examples for building integrated
photovoltaics. Federal building projects such as the “Federal Ministry of
Economics” (100kWp, 1998), the “Reichstags Building” (39 kWp, 1998), the
“Office of the Federal President” (44kWp, 1998) or the “German Chancellery”
(300kWp, under construction) got a photovoltaic installation.
Demonstration projects
like “Auf dem Kruge, Bremen, Germany” (208kWp), “Niew Sloten, Amsterdam, The
Netherlands", "Niewland, Amersfoort, The Netherlands” (1MWp), for the
solar initiative of the state government of Nordrhein-Westfalen for 50 solar
housing estates help to introduce photovoltaic to home owners and to the general public.
These projects were either initiated on government level or by local utility companies, who also
provide the funding or other subsidies for these photovoltaic projects. The already existing
projects helped to deal with the responsibility and ownership of a photovoltaic
installations and it´s maintenance as well as to learn about legal problems,
which still exist in many European Countries.
Photo
7: PV-Flat roof integration, 44kWp, Office of the Federal
President, Berlin
Photo 8: PV-Roof integration, 72,6kWp, “Sonnensiedlung”, Hettstadt
Large building
projects attract the attention of the mass media. They serve therefor ideally
as an image carrier and information base for photovoltaic. Project examples in Germany are the “Mecedes
Benz Factory Bldg., Bad Cannstadt” (435kWp, 1996), the “New Trade Fair Munich”
(1016MWp, 1997), the “Education Center, Herne Sodingen” (1 MWp, 1999) or the
new “Central Railwaystation, Berlin” (300kWp) which is presently under
construction. Those who initiated such projects not only take the profit of the
electricity production into account but also the benefits from the green image
of photovoltaic.
Major cost savings are expected by an
increasing use of prefabricated and integrated building elements with
photovoltaic. They will help to cut down the labour as well as construction
costs. Cost reductions of this kind allow to find additional funding for the
extra costs of a photovoltaic system on a building. The vision is to have
completely prefabricated building elements with integrated photovoltaic
(modules, inverter, cables, etc.), which will be just carried to the
construction site and will be put together on it. The market for such prefabricated building
components will increase for both, the renovation of existing buildings as well
as for the erection of new buildings.
For example: Germany got a new federal law “Stromeinspeisegesetz
(StrEG)”, which provides the legal base for selling and feeding photovoltaic
electricity into the public grid. It guarantees today a price of 0,45 US$/KWh)
to each person who feeds PV into the grid. In addition a number of other
subsidy programs help as well to get even closer to a cost effective photovoltaic
electricity production. In 1999 the German government started the “100-000 Roof
Top Program”, which provides additional subsidies for the investment costs of a
photovoltaic
system. Other financing schemes are independent from public money, such as the
“Full Cost Rates (FCR) for Solar Energy - The Aachen Model”[4]. Legal
agreements, which allow a number of share holders to own together a photovoltaic system,
also help to make photovoltaic systems financially more attractive to a larger
group of people.
Further photovoltaic product
developments should primarily focus on suitable applications for existing
buildings as most of the buildings of the year 2050 are already built in
Germany and maintenance, repair and renovation of these buildings will become
much more important in building construction than the erection of new buildings
[5].
Photo
9: PV-Overhead glazing, 1MWp, Education Center, Herne Sodingen
Photo 10: PV-Roof
integration, 1MWp, New Trade Fair, Munich
It can be seen from
the given examples that an integrated approach which takes into account the
synergy of power production and weather protection by the photovoltaic material,
results into a new concept which can make photovoltaic attractive to builders
and their clients. But it must be made clear that such a true solar
architecture need to be developed with specific elements developed for this
purpose and engineers and architects collaborating fully to develop them. In
Europe quite a number of different building integrated photovoltaic products are available on the market now. At
the same time we can fall back on the experiences of quite a large number of
buildings with integrated photovoltaic systems. Today we are in the position to say: photovoltaic technology
is ready for the building market.
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REFERENCES
[1] Prasad D., Schoen T., Hagemann I. and Thomas PC (1997) PV in the
Built Environment - An International Review. In Proceedings of ISES 1997 Solar
World Congress, August 24-30, Expo Science Park, Taejon, Korea
[2] Hagemann, I. (1998) Shading Systems with PV - A New Market for
Prefabricated Building Elements? In Proceedings of PLEA 1998, Lisbon, Portugal
[3] Hagemann, I. (1996) PV in Buildings –The influence of Photovoltiacs
on the design and planning process of a building. In Proceedings of World
Renewable Energy Congress (WREN), Denver, USA
[4] Solarenergieförderverein
e.V. (1999) Full Cost Rates (FCR) for Solar Energy (The Aachen Model). In
http://www.sfv./infos/soinf171.htm, Aachen, Germany
[5] Hagemann, I. (2001).
Gebäudeintegrierte Photovoltaik. Architektonisch sinnvolle Integration der
Photovoltaik in die Gebäudehülle. Verlagsgesellschaft Rudolf Müller. Köln,
Germany
Photo 1, 2, 8: Ingo B. Hagemann, Aachen, Gemany
Photo 3: Tobias
Grau KG, Hamburg
Photo 4: Saint
Gobain Glass Solar (SGG), Aachen, Germany
Photo 5: Braas
Dachsysteme GmbH &Co, Oberursel, Germany
Photo 6, 9: Pilkington
Solar International GmbH, Cologne, Germany
Photo 7: Solon
AG für Solartechnik, Berlin, Germany
Photo 10: Siemens Solar GmbH, München, Germany