The Solar Decathlon Europe is an international competition for universities from all over the world to design and build a self-sufficient home, grid-connected, using solar energy as the only energy source and equipped with technologies that permit maximum energy efficiency. An interdisciplinary team of architects, interior architects, structural engineers and building physicians at the Hochschule für Technik Stuttgart accepted the challenge and is working on the design of the building since October 2008. The basic idea of our design is to use traditional means of dealing with the climate in hot and arid zones and to combine them with new technologies. Thermal mass, sun shading and evaporative cooling will help to achieve a comfortable indoor climate with passive means. The key element of our passive cooling concept is a new building component that we call “energy tower”, which is also an important feature of the interior design. In addition night cooling via sky radiation and evaporation is used to discharge PCM material. Active cooling is supplied by a reversible heat pump powered by photovoltaics.