Storage of heated water in rock caverns is judged to be an interesting alternative for solving the storage problems connected to large-scale utilization of solar energy and surplus industrial heat. For verifying and demonstrating the technique, a test plant with a storage volume of 15 000 m3 will be constructed, in which a comprehensive research programme will be carried through. The effects of various time/temperature cycles will be studied. Main items on the research programme are: heat losses, rock stability, heat exchange and material questions, water layer studies, and influence on the environment.
The use of solar and wind energy as well as surplus or waste heat from industrial processes, power production, sewage water etc is judged to be an important way of reducing the very strong dependency on oil for heating purposes in Sweden. The increasing price on oil and the risk of disturbances of the supply together with the political decision on the limitation of use of nuclear power have lead to very strong efforts in Sweden to develop new techniques for the use of new energy sources and to reduce the need for energy. As the main part of solar and waste heat is normally available only during summer, this technique nessecitates seasonal storage. Extremely inexpensive methods will have to be used to make seasonal storage of low temperature energy economical. For large scale storage there are today few other choices available than storage in water or rock and soil. Since the "energy density" of such ·magazines is low, huge volumes will be needed to cover even a small part of the energy requirement for heating in Sweden. In particular storage of heated water in rock caverns or storage of heat direct in penetrated rock masses are judged to be most interesting due to common occurrence of suitable rock formations in Sweden and the possibilities this entails for optional localization of the storage close to the producer or user of the heat. The storage of heated oil in large rock caverns used in Sweden for many years has shown us that the use of rock caverns offers storage at low costs and that the energy consumption for heating the oil is small compared to the above ground alternatives. It was therefore natural to choose the same concept for the first heat storage facility in Sweden. The conditions for storing heated water in rock caverns have been studied in several R&D-projects in the 1970's. These investigations indicate that a large-scale storage in rock caverns can be advantageous from both technical, economical and environmental points of view compared to storage above ground. So far the technique has not been tested on a large scale.
For verifying the results of earlier investigations and for demonstrating the technique under realistic circumstances, full scale tests are necessary. For this purpose a test cavern, equipped with a comprehensive instrumentation for research, is now being designed.