in this paper it has been investigated the possibility to exploit the energy content of hydrogen released by green algae directly by a fuel cells stack. The power output can vary widely depending on the use of flow rate controls; since excessive dilution of hydrogen and power peaks can be avoided provoking a temporal delay between hydrogen production and the fuel cell stack feed. A 100 m(3) algae culture can give an average 240 W power for 100 h, taking in account also fuel cell efficiency. There are possibilities to increase the power output, overall rising algae efficiency to transform solar energy into chemical hydrogen energy. (C) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.