Energy efficiency is the key to buildings with minimized environmental
impact. The combination of this approach with active and passive sola
r energy utilization can lead to purchased energy demand close to zero
. Nevertheless, energy autonomy under Central European climatic condit
ions requires seasonal energy storage, especially energy with a high e
xergy content. The Fraunhofer Institute for Solar Energy Systems built
an energy autonomous house in Freiburg, Germany, in 1992. Highly effi
cient solar systems are combined with a hydrogen-based seasonal-storag
e system. Long-term storage of low-temperature heat was avoided by ext
ensive passive solar energy utilization. After describing the project,
this paper focuses on the experience of nearly 3 years of operation.
Copyright (C) 1996 Elsevier Science Ltd.