Solar-hydrogen energy system is one of the promising energy alternatives for the future which enhances solar energy utilisation. In this study different solar–hydrogen energy systems were studied: photochemical, photoelectrochemical, photobiological, electrolysis (photovoltaic and electrolyser) thermolysis and thermochemical methods. A survey of the state-of-the-art of these methods has been presented. An integrated photovoltaic/electrolysis system and a photoelectrochemical (PEC) system have been selected as showing more potential and promise for further study. On the basis of theoretical studies and assumptions a mathematical model has been developed for an integrated photovoltaic /electrolysis system. The model includes electrochemical and thermal aspects of the system. The model has been analysed and simulated for a silicon solar cell integrated with a hypothetical electrolytic cell, and shows similar results compared with that of water electrolysis in a photovoltaic driven electrolyser.