The "energy-autarchic solar house" (ISE, Freiburg 1991/92, Wilhelm Stahl) was built around the same time as the Passive House in Darmstadt. It is also very similar to the Passive House. The sometimes very complicated autarchic supply technology with hydrogen storage was not operated any more after the end of the measurement period. The passive technologies and the heat recovery proved to be very effective. Today the ISE tests the efficiency of Passive House compact heating units under practical conditions in this house. During the project construction, the Passive House Group exchanged information with the ISE and Wilhelm Stahl, and mutual support was provided by each.