To date, the topic of solar collector systems has primarily involved small-scale standard systems for single-family and double-family houses. Here, we would like to focus on the numerous large buildings which could also be provided with solar heat. While many blocks of flats, housing estates, hotels, halls of residence, hospitals and commercial buildings have large unused roof surfaces, the facades and balcony balustrades, or the roofs of adjacent buildings such as garages, are also surfaces which could be used for the heat supply.

Although photovoltaic systems of all sizes are currently in vogue, and the "small" solar collector systems are also selling well, the market for large-scale solar energy systems still needs to be stimulated.The chances of success are high, because large-scale solar energy systems offer a number of advantages: they provide more heat per square metre of collector surface, and are more cost-effective than small-scale systems. But which buildings are particularly suitable for large-scale solar energy systems? What is more profitable: to generate hot water only, or to also supply the heating system with solar heat? What dimensioning is optimal with regard to costs? Which system concept is the best? What are the typical planning errors or installation errors which should be avoided? What are the success factors for successful projects?

These questions are discussed here, on the basis of the German Federal Ministry for the Environment's energy research projects. The analyses relate to systems with a collector surface area of over 100 square metres, and buildings of various types. The emphasis is on the most cost-effective systems used purely for water heating, but initial results are also available for combined systems, which – with heightened heating costs – enable considerably more fossil energy sources to be saved.

Solar-supported local heating networks, systems for solar cooling or air conditioning, and process heat generation constitute another research area in the german Solarthermie2000plus programme, and are not discussed here.