Algae can contribute to securing our future energy supply by providing biomass for biodiesel production. Besides, the biomass from algae can be used for generating electricity. Algae modified for production of certain proteins or pharmacologically active substances, moreover, are of interest to the cosmetics and pharmaceutical industries. For the above reasons, algae are increasingly grown in bioreactors. These reactors often consist of vertically arranged transparent plates or tubes holding the algae material and a culture medium. Due to their narrow upright shape, such reactors, however, do not optimally use the sunlight from above. Carbon dioxide-enriched air is introduced with high pressure into the tubular reactor or plate reactor. Using large amounts of energy, the algae material, in addition, must be circulated constantly by means of pumps. Algae can contribute positively to energy supply if the energy yield from biomass exceeds the energy expenditure for operation of the reactors. Researchers from KIT's Institute of Process Engineering in Life Sciences have developed a photobioreactor that enables an energy-efficient production of algae. The reactor is made up of two horizontal Plexiglas plates in between which one finds the algae mass and culture medium. It is due to this structure that only a minimum hydrostatic pressure is created in the reactor. Since the plates are designed like an accordion, the surface of the reactor is about four times as large as the area needed for the reactor setup. The angles of the zig-zag folds have been designed for optimal light incidence for algae growth. The algae grow so fast that in the open air, approximately one third of the algae biomass can be harvested each day. In addition, it is possible to provide the lower Plexiglas plate with a membrane for permeation of air and carbon dioxide. Due to this measure, the energy expenditure for supplying gas is much lower than when using tubular reactors.