The use of solar energy is of great interest to many applications, but the discontinuous supply of energy is in general not tolerable, therefore, to provide a reliable energy source to consumers it is necessary to employ energy storage systems. Various types of energy storage systems are compared with respect to energy densities and cycling periods. Today there is no technology available for seasonal energy storage. A novel hydrogen/oxygen storage system is under development as part of the "Self-sufficient Solar House 2000", which will be built in Freiburg within the next two years. © 1990.