Solar Energy System of the Month:

Power Generation with Perspective:
Transparent POWER-Cells for Innovative Solar Architecture

German Sunways Inc. in Constance is moving to a new direction. The company, which has been listed on the stock market since February 9, 2001, develops products and solutions for the production of solar electricity. The award-winning POWER-Cell (Polycrystalline Wafer Engineering Result) offers architects and planners new possibilities for the design of aesthetic, high quality facades, which produce energy from sunlight.

POWER-cells, Sunways Inc.
POWER cells from Lake Constance, Germany
Photo: Sunways Inc

Active and Attractive Facades

Glass façades on office buildings, winter gardens or sunroofs on automobiles will become energy suppliers with the transparent solar cell. Modules with translucent POWER-cells can be directly integrated into the façade. All commercial types of glass are suitable, from laminated safety glass to heat insulation glazing; even curved surfaces can become solar generators with POWER-cells. The use of the transparent, dark blue solar cells allows a beautiful play of light and shadow. Innovative architects and building owners can even install colored POWER-cells.

The standard product lets a tenth of the light pass through and has a 10 percent efficiency rate. In the future, cells which will allow up to 30 percent of the light to pass through, will be manufactured on demand. Large-surface Photovoltaic systems will be possible with the new technology, and it will still be sunny inside the building. The incoming light will be absorbed only a bit-an effect that will certainly be pleasing. The transparent modules replace the traditional shadow-creating elements, contribute to the lowering of building costs and reduce energy expenditure for cooling rooms. The special surface structure of the POWER-cell should, if vertically mounted, increase the energy yield of PV systems even more.

POWER-cell transparent
Photo: Sunways Inc.

New Production Technology

The transparent solar cells were made possible by a new manufacturing process. Peter Faht and Gerhard Willeke of the University of Constance investigated the basics of this process as one of the European Community's sponsored projects. Hair-thin grooves are cut into the silicium wafer, the foundation of the cell, in both directions. A translucent, microscopic structure of holes is formed where the 90-degree indentations meet. The basic raw material for the solar cells is polycrystalline silicium. The standard POWER-cell measures 10 by 10 centimeters and is about 0.3 millimeters thick. It produces, according to the type of cell, between 0.6 and 0.9 watts. The Sunways cells can be integrated into modules in various sizes-up to 2 by 3.5 meters. They yield a peak output of 80 watts per square meter. Sunways Inc. emphasizes that ecological issues are being taken into account during manufacturing. The silicium wafers, on which the cells are based, originate from European facilities, which largely use CO2 neutral energy, that is produced in hydraulic power stations.

full-scale POWER-cell

Photo: Sunways Inc

POWER for Inside and Outside

Transparency, energy production and shadowing effects should improve the use of solar energy systems, also in practice. The first example of a successful integration of POWER cells can be viewed in Kirchzarten near Freiburg. There, the guests of the "Solar Café" can enjoy their cappuccino on the shady terrace in summer, while the solar energy system located above their heads delivers a peak output of 1 kilowatt. Four vacuum pipe collectors supply hot water and also support the heating system. A wood pellet boiler is used for back up heating.

The Constance company recommends its double-sided photosensitive solar cells not only for facades, but also for noise protection walls. The POWER-cell should be able to be used independent of orientation, in contrast to traditional, opaque cells, which have the most optimal production if oriented southward with a 35-degree angle. Automobile industry suppliers have also discovered the advantages of the translucent solar generator: they want to install the POWER-cells in sunroofs.

Sunways Inc. estimates good market opportunities and wants to expand production considerably. Using the additional capital from going public and the support of the German Federal Foundation for the Environment (Deutsche Bundesstiftung Umwelt - DBU), POWER cells shall be mass-produced and the efficiency rate is to be raised. The launch on the stock exchange was successful: the Photovoltaic specialists' first stock quotation rose to 13 Euros. The "solar stocks" had, with that, an 85% increase from their issuing price of 7 Euros.

Solarcafe Kirchzarten
Solar Café in Kirchzarten
Photo: Sunways Inc.

Material and Photos: Sunways Inc.
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Translation: Mary Meier


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