Energy storage is a key technology for establishing a stand-alone renewable energy system. Current energy-storage technologies are, however, not suitable for such an energy system. They are cost ineffective and/or are with low energy-conversion efficiency. Hydrogen generation and storage from water by sunlight is one of these technologies. In this study, a simple concept of hydrogen generation from water by using sunlight, “concentrated photovoltaic electrochemical cell (CPEC)” is proposed. It is experimentally shown that the CPEC operates stably and achieves conversion efficiency from light to hydrogen energy of over 12%.