Self-Sufficient Solar House, Freiburg, Germany. This house utilises solar energy for all its energy needs. The building has several innovative features that give it a high thermal inertia (meaning it is slow to react to external temperature changes). In addition to this, hydrogen and oxygen (produced by electrolysis) are used in a storage system which enables the inter- seasonal storage of energy. The house was built as a demonstration project by the Fraunhofer Institute for Solar Energy Systems. Photographed in 2005.