Modelling of an Ultraviolet based Hydrogen and Oxygen Generation System

The solar spectrum contains a fraction of ultraviolet radiations that can cause serious health issues. A novel system is proposed and investigated to harness the terrestrial ultraviolet radiations to produce hydrogen and oxygen. The overall system, designed to work with radiations having UV index greater than 11, comprises of 1) an active optical subsystem to concentrate the solar radiations, 2) a desalinator to reduce the water salinity, 3) a steam generator to generate superheated steam, and 4) solid oxide electrolyzer to produce hydrogen and oxygen. The ultraviolet radiations are concentrated on a customized micro sized honeycomb structure of gallium nitride (GaN) that is mounted on the steam generator, made of Cu-Ni composite, in order to enhance the radiation absorptance. Through finite element modeling, the UV absorptance coefficient on the flat surface and honeycomb structure are found to be 48.98% and 93.43%, respectively indicating a considerable improvement in the ultraviolet radiation entrapment due to modification of the surface morphology. The simulation further revealed that the overall system requires 0.5 kW thermal power to generate superheated steam of 500·C and 1.3kW electrical power to generate 7 slpm (standard liter per minute) of hydrogen. The thermal power required to maintain a steady operating temperature of the electrolyzer is found to be 0.2 kW. The required thermal power can be obtained by designing an active optical system comprising Fresnel lenses offering 30 suns concentration of ultraviolet radiations and the required electrical power can be obtained by ultraviolet-based GaN tandem photovoltaic solar cell array comprising of 350 units with surface area of 0.1cm2.)