There is a variety of different possible designs for autonomous power supply systems. The final choice depends on several factors. The present investigation focuses on a typical combination of equipment and only deals with electricity production. The possibility of generating heat for hot water and heating supply is not addressed.

Hence, the model system basically comprises a photovoltaic unit, an electrolyzer, hydrogen storage, and a fuel cell. Wind energy converters and motor generators can be added as energy sources. All parts are connected to an internal grid by power conditioning units. A DC/AC-inverter produces the alternating current required for end-use. A final, but very important component is the controller for managing the energy flows.

Hydrogen can be stored as a compressed gas or a cryogenic liquid. Both forms are not economic at a small scale. Therefore, instead of a single house a small community (e. g. a village) figures as consumer.

Apart from the equipment already mentioned the system requires an additional storage to meet load fluctuations and peak demands, since a fuel cell or a combustion engine generator have relatively long start-up times. Therefore it is reasonable to install a smaller but faster energy storage unit such as a battery or a high capacity capacitor. Even the utilization of a small PEM fuel cell may be considered.

The overall system configuration, as treated by the simulation program, is shown in Figure

1.