By Willi Ernst

Inseparable--Own Consumption and Building Integration

Numerous PV systems on building fronts and roofs prove that the integration of solar modules directly into a building is possible. The modules do not only produce clean energy, they fit into the building in an optically attractive manner. However, photovoltaic systems that are part of buildings and the integration of solar modules into buildings also have clear technical advantages:

Especially, photovoltaics fit the daily consumption profile perfectly. The energy is produced where it is consumed. There are no additional line losses, and no losses through the transformation into the high and/or medium voltage grid or from the grid to the service line level.

This makes a relief of the grids and thus the occasional increase of the grid capacities possible, as well as prolonging the service life of the grid infrastructure.

In addition, building-integrated PV systems can make a substantial contribution to the substitution of other building materials and are thus ecologically desirable for new buildings and rehabilitations.

These facts are all well known in the solar industry. Architects and planers, on the other hand, still get bellyaches at the thought of photovoltaics in buildings. In politics, the realization also has not yet hit how positive a BIPV remuneration category--similar to the ones in France or Italy--would be as guidance. This approach is also missing so far in the draft of the EEG amendment, although an expansion of the own consumption regulation already points in the right direction, namely away from the mainstream of purely yield-driven (industrial-scale) installations with crystalline standard modules or bargain thin-film systems towards the application of solar energy generation at the main consumption location of electrical energy, from residential to industrial buildings.

Own Consumption--Great Potential for Solar Roofs

In view of the enormous price pressure the PV industry in Germany faces at present, solar roofs are an important aspect. For when standard installations reach the limits of profitability, solar roofs that also have additional functions beside the generation of energy, are the clever alternative. The use of thin-film systems with the described advantages (good return rates even on flat roofs and in case of unfavorable locations) is ideal for huge areas of slightly inclined industrial roofs, even with a north-south apex.

This is especially exciting in light of the own consumption regulations in the EEG. Power generated with solar modules that is consumed on-site before feeding it into the public grid is overall better compensated than directly fed-in power due to the combination of avoided costs for purchasing power and the feed-in remuneration. This promotes not only the generation of power close to its consumption, i.e., photovoltaic systems that are part of buildings, but also a change in behavior regarding energy consumption. Load shifts, i.e., a shift of energy consumption during production peaks of the PV system, relieve the grids and are therefore a first and important step towards ‘Smart Grids‘, with which the generation and consumption of energy is controlled intelligently and adapted one to the other.

BIPV--Long, Perfected History

Markets with different political guiding principles for the expansion of photovoltaics already realized this some time ago: after the boom of free-standing installations, Spain introduced a higher remuneration for building-integrated systems; South Korea, Italy, France, Switzerland and increasingly other countries make the following version appealing through increased feed-in rates and/or special subsidies: photovoltaic components for the generation of electricity that have at least one other function in the building. The forerunner country is, as it is so often, Japan. Since PV systems there were installed primarily on private residential roofs based on ecological motivation rather than financial considerations, they paid much more attention to a successful combination of technically efficient and at the same time aesthetically attractive roof integration. This is why the former PV world market leader still is the doyen concerning building integration today. According to estimations by experts and information from Japanese market leaders, significantly more than 10 MW PV modules in different shapes are integrated in roofs there: from narrow and oblong modules the height of bricks, to rectangular standard module shape to square solar roof tiles. The latter is widespread in a system called ‘Tatami’, which takes up the square shape--and thus a cultural standard as it is immortalized in the rice straw mats of the same name.

Solar Roof Tile

Another home country of the solar roof tile recently introduced a feed-in regulation that also considers this leading work: Switzerland now offers significant premiums for building-integrated modules. The Newtec solar roof tile with a special plastic profile, which is still holding its own on the market today, and the Solrif aluminium frame system, which makes the refinement of every glass module into a ‘solar roof tile’ possible and represents probably the largest volume in the in-roof area, were already developed here at the beginning of the 90’s. This makes it possible for some module manufacturers to use their basic product also as a roof-integrated solution. Since recently, there is also a CIS thin-film version by Sulfurcell available. With the in-roof systems by Solarfabrik, Schott, Photowatt and CentroSolar, meanwhile already 1-2 MW modules are turned into solar roof tiles in one month alone. Here, successful classy looks with black mono crystalline cells, black Tedlar foil and black covering frames are in demand, as shows the great success of the C 21e by SolarCentury in England and the in-roof system S-Class Deluxe by Centrosolar throughout Europe.

PV roofs are becoming ever larger, trend turned towards solar roofing systems.

However, the rapid price deterioration that can be observed at the moment and the resulting pressure on effectiveness for PV systems also help to advance the development of new BIPV technologies. For only when photovoltaics are multifunctional and able to offer substitution costs for saved building materials, is it viable in the long term. This is the most obvious and easy in the area of roofing. Here, solar modules can quite easily be turned into water-draining layers, make a positive visual contribution to a building and in addition generate power. The oldest BIPV technology is, therefore, the roof integration, from what are known as solar roof tiles to complete-roof systems. The fears to have to accept worse yields due to missing ventilation have long since been refuted: the well thought-out design of the solar roof shows at least adequate yields and has paved the way for the triumphant march of the solar roof tile.

Thin-film, the Perfect Solution for Building Integration

New systems such as TF Plate Professional and TF Multi Professional by Centrosolar are so light due to the flexible thin-film laminates on carrier plates that they are used by the square kilometer on bitumen or trapezoidal roofing of industrial roofs, where the installation of classic PV systems is not possible for static reasons. This applies in addition for the latter system to all types of foil roofs. The TF membrane system, which contains PV laminates directly on a PVC-free plastic membrane, was developed for even larger installations, since it is possible to rehabilitate all types of flat roofs with it, in addition to bitumen, PVC-foil and EPDM roofing felt. This and similar ‘solar roofing felt’ has already been established for more than 10 years on German and American roofs and shows especially good yield.

The reason for this are namely the positive temperature characteristics of the cells used in the ‘solar roofing felt’ made of amorphous silicon, the only photovoltaic material that has not only an especially low temperature coefficient, but also undergoes a performance increase through what is known as the annealing effect due to high temperatures.

Symbiosis of Architecture, Aesthetics and Photovoltaics

The new Centrosolar office building in Paderborn, Germany--also as a Biohaus (ecological house)--shows clearly: modern ecological architecture in combination with solar power generation and an aesthetically pleasing look is possible. The three-story building--with particularly high insulation standard and ecological house technology a passive house--includes 11 different solar systems that are installed on, in and on top of the building in a visually appealing manner. Here, almost the entire range of the application options of PV is represented on and in the building: from semi-transparent entrance roofing, bi-facial balcony enclosures, ventilated facades with thin-film modules, and various cell types integrated into the glass curtain wall to solar roofing felt suspended above or integrated directly into the roofing to the tracking installation crowning the building and evacuated-tube collectors mounted on the facades, everything that demonstrates current and future trends in solar technology can be seen here. It is therefore considered a showcase for building-integrated photovoltaics and is mentioned as an example in presentations and publications throughout Europe.

A very special architectural concept has now been developed at the Bauhaus University of Weimar and represents an entirely new challenge for photovoltaics: the Screenhaus.Solar. In the context of ‘90 years of Bauhaus’ professors and a group of students designed, developed and realized this eye catcher in only one semester. The Screenhaus is a building for multimedia use in the shape of a hyperboloid, asymmetrically parabolic in longitudinal direction. This mathematically defined, efficient bowl shape is put together from rod-shaped elements--simple wood slats--that are arranged in the room distorted against each other and connected at certain points.

The impermeability of the building was produced by applying a colored membrane to the inside of the grid, which is connected to the structure at certain points on the bolted knots. The Screenhaus.Solar became solar by--temporarily--attaching solar roofing felt by Centrosolar AG, which generates the solar power for the screenings-based on calculations, since it is time-delayed. A planned further developed version, ‘Screenhaus.Solar 2.0’, is even to have a shell that is completely power generating. For meanwhile, the Swiss StartUp Flexcell has successfully integrated its amorphous silicon cells directly into tent fabric similar to awning material so that a tailor-made reddish building shell with consistently integrated photovoltaics seems realizable. The future has already begun after all.  

Willi Ernst is a member of the Advisory Board of Centrosolar Group AG (http://www.centrosolar.de/). Ernst is expert for Building-Integrated Photovoltaics (BIPV).