Experimental and theoretical investigations of a new integrated solar tower system for photocatalytic hydrogen and power production

Abstract

Solar energy conversion via photocatalytic hydrogen production from water is an attractive route for the propagation of a hydrogen economy. Increasing the efficiency of such systems to meet the target of 10% is essential for industrial their adoption. A new hybridized system employing a photocatalytic reactor and photovoltaic cells in a cavity receiver of a solar tower system is proposed. A fully functioning lab scale system, capable of handling continuous flow processes, is built, and experiments are conducted to investigate the behaviour of this system. Production of hydrogen in the photo-reactor is observed to increase with an increase in temperature and a decrease in the pressure to below the atmospheric pressure. A maximum quantum efficiency of 1.9% is achieved with a 77% - 23% ratio of CdS – ZnS mixture under a visible light source. With power output from the light harnessed by the photovoltaic cells, the energy efficiency is increased from 0.2% to 2%, respectively. The optimal flow rate for an electrolyte concentration of 0.3 M and reactor volume of 90 ml is determined to be 50 ml/h. A thermodynamic study of a proposed large scale system is conducted. This system combines a photocatalytic process, a photovoltaic process, and a heat engine to efficiently utilize solar radiation. For a given solar tower system that requires a reflective area of 913, 289 m2, energy and exergy efficiency values up to 40% and 30% are achieved respectively. Based on archived solar data, for a given summer day the system produces 50 tonnes of hydrogen if outputs from the photovoltaic process and the heat engine are used to run an electrolyzer.