System engineering aspects and power electronics in an autonomous photovoltaic-hydrogen system

System engineering aspects have to be considered when designing an autonomous photovoltaic-hydrogen system (energy supply without grid connection). Power electronics plays an important role in such a system in order to achieve a high total efficiency of the system by decoupling via power electronics. Through that all the devices can be operated in their maximum power or maximum efficiency operation points. Large photovoltaic generators e.g. operate advantageously with a high system voltage to reduce wiring losses, whereas the development of high efficient electrolysers and fuel cells, optimised for operation in a solar system, leads to a low voltage layout. Therefore the use of Power electronics (DC-DC-converters) is convenient to transform the voltage levels and have an additional degree of freedom in designing the electrolyser/fuel cell which results in highest overall efficiencies. New DC-DC-converters are described, which use the autotransformers advantages. For the fuel cell the autotransformer is used in a boost circuit, whereas for the electrolysis a new high efficient, low cost, resonant DC-DC-converter based on the buck circuit is used. Examples of achievable efficiencies are given and the system layout and measurement results of the 40 kW-autonomous photovoltaic-hydrogen system in Julich (FRG) are presented.