Suitable exteriors for solar arrays exist nearly everywhere. A south-facing surface is ideal for the installation of a solar power plant, but not necessary. The angle of the surface is even less important: solar modules can be mounted on either flat or peaked roofs as well as on facades. More critical is that no trees or other buildings cast shade on the solar cells and thus reduce their efficacy.

Summer Sun - Winter Sun

The sun in its daily east-west traverse over western Europe describes a high, almost vertical arch in summer, and a flatter, more southerly path in winter. The angle of the sun's rays, therefore, changes gradually with the seasons. An ideally directed pv-system would follow the sun's path, as the performance of solar cells depends not only on the intensity of the radiation, but also on the angle of incidence. The density of the rays is highest when the photons reach the cells at an angle of 90°, where energy loss through reflection is also at its lowest. Static solar power arrays must compromise -- panels can sometimes be adjusted to a winter or summer position. For a larger array, the investment in an automatic tracking system with electrical motors is worth it.

Innovative Solutions, New Concepts

In order to optimize the solar "harvest" all day long, the solar modules track the sun vertically and/ or horizontally. The energy yield can be thus increased -- depending on the geographical location -- by around 23% in northern Germany and up to 30% in southern Germany. Hamburg's SunTechnics GmbH has developed tracking solar power systems which should fulfill the highest technical and aesthetic standards.

SunTechnics GmbH erected solar power plants on the roofs or grounds of 12 Shell gas stations, 3 of which are tracking systems.
A "PV-Pylon" (mast) was placed at the Shell-Autohof in Herbolzheim on the Autobahn Frankfurt-Basel (A5) in September 1999. It has a panel surface area of 21 m² and follows the sun's path from east to west and high to low. Another system of this type was built on Sylt in the North Sea. In March 1999, the "Sun Sail" on the roof of the Shell station "Steilshooper Allee" was christened.

Shell sets the Sun Sail

Shell AG, which operates the world's most modern solar cell factory in Gelsenkirchen, continues to send wide-ranging signals. The "Sun Sail" is one of several projects which emphasize the oil concern's engagement for renewable energies. It combines the optimal use of the gas station roof with a distinct increase in the solar "harvest" in comparison to an anchored pv-system. After all, the Sun Sail produces around 1950 kilowatt hours per year, with a peak capacity of 1.8 kWp. Expected is a total yield of 3500 kWh per year from the power plant on the gas station roof, together with a conventional pv-system. In addition, the aesthetically convincing system stands out visually -- and such visibility was a consciously desired effect of this investment in modern solar technology.

The details were carefully researched. The newly-developed controlling concept reduces the energy consumption of the tilting mechanism to less than 0,3 % of the yearly output. The module surface of 20m² has an angle of inclination of 30° and can be swiveled 55° to either side. The output of the solar generator is listed at 1,8 kWp.

From East to West -- and Up and Down

A differently conceived sun-tracking pv-system stands on a 10 meter high mast on the Autobahn 5 -- or more precisely at the rest stop Herbolzheim. Here the modules move horizontally as well as vertically. Yet the system still functions with only one motor. An optimized rail guide lowers the system's own power consumption to a minimum of 0,3% of the yearly output.

An advantage of this solution: the mast only requires one square meter of space on the ground -- thus can pv-Pylons be installed where no suitable roof is available, or little open ground is free.

SunTechnics GmbH has already applied for patents on their innovative construction. The company will soon go into factory production, fulfilling contracts in Germany and abroad.

Material and graphics: SunTechnics GmbH, Hamburg. Text: Rolf Hug, Red. Solarserver. Translation: Genevieve Cory.