Renewable energy-hydrogen systems for remote applications constitute an early niche for sustainable hydrogen energy. optimal matching between the photovoltaic (PV) system and the electrolyser is essential for maximum electrical energy transfer and hydrogen production. This paper investigates the possibility of achieving near maximum power transfer between a directly coupled PV array and a proton exchange membrane (PEM) electrolyser stack by finding an optimal configuration of series-parallel connection of both the PV panels and the PEM cells. The application of this procedure to four 75 W PV modules directly coupled to five 50 W PEM electrolyser stacks (250 W in total) predicts an energy transfer of over 94% of the theoretical maximum. initial experiments indicate an actual energy transfer of around 95%. Clearly, energy-efficient direct coupling is advantageous economically since the costs of an electronic coupling system (around US$ 700 kW(-1)) are avoided entirely. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.