'Green' Energy From Algae

Microalgae are monocellular, plant-like organisms engaged in photosynthesis and converting carbon dioxide (CO₂) into biomass. From this biomass, both potential resources and active substances as well as fuels like biodiesel may be produced. While growing, algae take up the amount of CO₂ that is later released again when they are used for energy production. Hence, energy from algae can be produced in a CO₂-neutral manner contrary to conventional energy carriers.

Apart from CO₂-neutral closed loop management, algae have an-other advantage: Industrial CO₂ emissions may be used as a “resource”, as algae grow faster at high carbon dioxide concentrations and, hence, produce more biomass for energy production.

However, this is not their only advantage: “Compared to land plants, algae produce five times as much biomass per hectare and contain 30 to 40% oil usable for energy production”, says Professor Clemens Posten, who directs this research activity at the KIT Institute of Life Science Engineering. As the algae may also be cultivated in arid i.e. dry, areas not suited for agriculture, there is hardly any competition with agricultural areas. There, however, closed systems are required.

Presently, algae are being produced in open ponds in southern countries of relatively small productivity. This is where Posten’s new technology starts. “In terms of process technology, our approach is completely different, as we are working with closed photobioreactors”, underlines the scientist. “Our plants convert solar energy into biomass, the efficiency being five times higher than that in open ponds.” The plates in usual photo-bioreactors are arranged vertically.

“Every alga sees a little bit less light, but the plant is operated at increased efficiency”, emphasizes the biologist and electrical engineer. Modern designs under investigation will find more intelligent ways to light distribution.

Consequently, algae production does not only work in countries with an extremely high solar irradiation. Most algae need a maximum of ten percent of the incident sunlight intensity. According to Posten, the remaining fraction would just be wasted. Posten points out that the Sahara offers just twice as much sun as Central Europe. But there, the reactor contents would have to be cooled. Other advantages of the closed system are drastic savings of water and fertilizers. Double use of algae for the production of food or fine chemicals and subsequent energy production from the residual biomass may also be conceivable.

Posten’s institute hosts one of the two KIT working groups focusing on research in the field of algae biotechnology. “As far as the development of photobioreactors is concerned, we are among the three locations worldwide, where considerable progress is being achieved in both process technology and biology”, explains Posten.

To close the cycle for the complete use of algae biomass for energy production, KIT researchers have more in mind. The biomass remaining after extraction (60 – 70%) is planned to be converted into other energy carriers like hydrogen or methane by means of the hydrothermal gasification process.