Hydrogen generation by water electrolysis was carried out using solar cells. As the electrolyte, sulfuric acid solution was used. As a reference, a single electrolyte cell of solid polymer membrane was used too. Mono- and poly-crystalline silicon solar cells were employed. The output of solar cells was connected to the electrolytic electrodes directly. The conversion efficiency of solar energy to generated hydrogen energy was evaluated. The hydrogen production for one year was estimated on the base of measured data of solar radiation, and the effect of reduction of CO2 production by exchanging fossil fuels (LPG and Town gas) with hydrogen was evaluated.