Algae are “lower” plants that live in water.

Algae can be very small (microalgae) and consist of only one cell, but they can also be huge and up to 100 m long (macroalgae, especially brown algae). Like “higher” plants, they also produce oxygen and therefore contribute significantly to the binding of atmospheric carbon dioxide. Algae can be found in fresh water, salt water and also in moist soils. Millions of years ago, blue-green algae or cyanobacteria helped to produce oxygen in sufficient quantities for life to develop. In addition to the food and cosmetics industry, algae can also be used as fertiliser in agriculture. However, algae, especially microalgae, can also be used to produce energy (biogas, biodiesel, bioethanol and hydrogen). Algae can be cultivated either in natural ecosystems, in aquacultures or in photobioreactors.

Compared to land plants, algae have a growth rate up to 30 times higher. Algae grow so fast that in industrial production, one third of the biomass can be harvested every three days. In photobioreactors they can be produced in a particularly space-saving way and under controlled conditions. There are different designs for this purpose; some of them are cultivated in kilometre-long tubular systems. These have the advantage that the algae receive light from all sides and, compared to open systems, are protected from environmental influences.