Energy efficiency is the key to buildings with minimized environmental impact. The combination of this approach with active and passive solar energy utilization can lead to purchased energy demand close to zero. Nevertheless, energy autonomy under Central European climatic conditions requires seasonal energy storage, especially energy with a high exergy content. The Fraunhofer Institute for Solar Energy Systems built an energy autonomous house in Freiburg, Germany, in 1992. Highly efficient solar systems are combined with a hydrogen-based seasonal-storage system. Long-term storage of low-temperature heat was avoided by extensive passive solar energy utilization. After describing the project, this paper focuses on the experience of nearly 3 years of operation.