Hydrogen is a kind of green fuel, and is considered as the substitute oil fuel for future. Although many of literature of photocatalyst water splitting have been presented, little of the literature focused on their energy conversions. Therefore, investigation of their energy conversions is carried out by simulation in this paper. Large energy is consumed in the plant for 1000 m(3) hydrogen fuels. In where, the efficiencies of hydrogen fuel generation are 29.9%, 15.6%, 10.5% and 7.95%, corresponding to the cases of one, two, three or four photons are needed to excite and generate one free electron by artificial light. While nature sunlight is utilized, the efficiencies are 48.4%, 25.2%, 17.8% and 13.6% corresponding to the four cases respectively; and the ratio between the combustion heat of generated hydrogen fuels and the total electric energy consumption is 319.0-333.0 %. (C) 2015 Elsevier Ltd. All rights reserved.