SOLAR PHOTOPRODUCTION OF HYDROGEN - A REVIEW

The concept of using solar energy to drive the conversion of water int o hydrogen and oxygen has been examined, from the standpoints of: pote ntial and ideal efficiencies; measurement of (and how to calculate) so lar hydrogen production efficiencies; a survey of the state-of-the-art and a technological assessment of various solar hydrogen options. The analysis demonstrates that the ideal limit of the conversion efficien cy for 1 sun irradiance is similar to 31% for a single photosystem sch eme and similar to 42% for a dual photosystem scheme. However, practic al considerations indicate that real efficiencies will not likely exce ed similar to 10% and similar to 16% for single and dual photosystem s chemes, respectively. Four types of solar photochemical hydrogen syste ms have been identified: photochemical systems, semiconductor systems, photobiological systems and hybrid and other systems. A survey of the state-of-the-art of these four types has been presented. The four sys tem types (and their sub-types) have been examined in a technological assessment, where each has been examined as to efficiency, potential f or improvement and long-term functionality. Four solar hydrogen system s have been selected as showing sufficient promise for further researc h and development: (1) photovoltaic cells plus an electrolyzer; (2) ph otoelectrochemical cells with one or more semiconductor electrodes; (3 ) photobiological systems; and (4) photodegradation systems. Several r ecommendations have been made for future work in this area. Copyright (C) 1996 Elsevier Science Ltd.