When exposed to sunlight purple bacteria produce hydrogen from water and organic substrates by photosynthesis. In this paper a technical approach to utilize this effect as an energy source is presented including the development of a suitable reactor concept. Phototrophic bacteria have special requirements concerning pH-value, temperature, light intensity etc.. Therefore natural or daily fluctuations of weather conditions cause severe problems for outdoor cultivation of this species. A new bioreactor concept with very low need of external energy was tested overcoming many of these problems and easing application of biological hydrogen evolution on a technical scale.