Hydrogen fuel for fuel cell vehicles can be produced by using solar electric energy from photovoltaic (PV) modules for the electrolysis of water without emitting carbon dioxide or requiring fossil fuels. In the past, this renewable means of hydrogen production has suffered from low efficiency (2-6%), which increased the area of the PV array required and therefore, the cost of generating hydrogen. in this research, the efficiency of the PV-electrolysis system was optimized by matching the voltage and maximum power output of the photovoltaics to the operating voltage of proton exchange membrane (PEM) electrolyzers. The optimization process increased the hydrogen generation efficiency to 12% for a solar powered PV-PEM electrolyzer that could supply enough hydrogen to operate a fuel cell vehicle. (C) 2008 GM Global Technology Inc. Published by Elsevier Ltd on behalf of International Association for Hydrogen Energy. All rights reserved.