Building Integrated Photovoltaics
New Developments and Trends in Europe

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.

INTRODUCTION

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.

Building Integrated Photovoltaic (BIPV)

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.

Building facade panels

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 2^nd to the 5^th 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

Semi-transparent facades

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.

Shading systems

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

Roofing materials

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

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

Photovoltaic Building Integration in the context of energy production

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].

Trends on the Building and Photovoltaic market

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:

Building Integrated Photovoltaic for Government Buildings

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.

Housing Estates with Photovoltaic

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 Integrated Photovoltaic Projects

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

Prefabrication of Building Components with 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.

Legal Base and Financial Support for Photovoltaic

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.

Increasing importance of Renovation of Buildings

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

Conclusions

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.

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 https://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