Solar Energy
...l. The hot water supply at the house in Freiburg is generated by solar collectors on the roof and hot water boilers in the basement. The electricity supply is based on photovoltaic generators on the roof which do not only meet immediate needs but also charge up batteries for the night. They also operate an electrolysis unit to produce hydrogen which is stored for dark winter days. This very expensive step towards 100-percent self-sufficiency has been the subject of criticism because energy-independence geared to individual houses is not a rational model. Be that as it may, the house incorporates an entire range of technologies in an experimental, but highly intelligent, way. It also demonstrates that it is possible to design housing without an external, non-solar energy supply. Experimental houses of this kind--as well as their more economically viable relatives, i.e., low-energy houses which require a maximum of 7.5 liters of heating oil per square meter per year (a new norm for state subsidies)--do make great demands on construction physicists to the extent that they call for much more than relatively good heat insulation. In the meantime, solar collectors are becoming a more common sight on rooftops. Not widely known is the fact that a small boom has also developed in Germany recently, with some 300,000 square meters of solar collectors being sold each year. Over one million square meters of collectors ha...