Thermodynamic analysis of efficiency of power units using hydrogen as a fuel as well as basic results of high-pressure H-2/O-2-steam-generators experimental modeling is presented. It is shown that at capacities of power units more than 10 MW, steam-turbine hydrogen units are preferable than fuel cell power units. Experimental, up to 25 MW(t) capacity, H-2/O-2-steam generators were created and the peculiarities of their use in steam-turbine hydrogen power units were experimentally studied. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.