Due to their high efficiency fuel cells are considered as an important technology for the rational use of fossil resources and the reduction of greenhouse gas emissions. Apart from the mobile applications, fuel cell systems have been developed especially for stationary applications in residential buildings. The technical requirements for energy supply systems vary widely depending on the different heat and electricity demand of the buildings. Moreover conventional supply systems are already established in the market. Fuel cells are therefore required to compete with technical and-even more important-with economical parameters of the competing systems.