Seasonal Thermal Energy Storage in Germany

Since 1993 German research work has been made in the Research and Development programs, "Solarthermie-2000" and "Solarthermie2000plus". One aim of the programs is to improve and demonstrate the technical and economic feasibility of different seasonal thermal energy storage concepts and technologies. The research work comprises basic Research and Development on storage concepts, design, construction, and long term monitoring and evaluation of (so far) eight large scale demonstration plants. The demonstration plants are designed to cover between 35 and 60% of the annual heat demand of new housing areas by solar energy. The first plants of the program are in operation since 1996. The data and experiences show that all investigated storage concepts are working without major technical problems. The annual heat output of the stores strongly depends on the return temperature of the connected district heating net which is determined by the heating systems of the connected consumers. Obviously a low temperature heating system in buildings is necessary to optimize the thermal output of the seasonal heat storage systems.