FUELS – HYDROGEN PRODUCTION | Photothermally and Thermally-Assisted Photovoltaic

Abstract

Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis; Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis; Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis; Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis; Photoelectrochemical Cells: Dye-Sensitized Cells; Fuels – Hydrogen Production: Photoelectrolysis. An overview of solar direct, solar indirect, and hybrid thermal processes for the generation of hydrogen is presented, and compared with non-thermal solar-based alternatives. The energy source (sun) and reactive media (water) for solar water-splitting are readily available and provide a renewable source, and the resultant fuel (hydrogen) and its discharge product (water) are each environmentally benign. In particular, a hybrid solar–thermal plus electrochemical process substantially increases the hydrogen that can be produced with solar energy via a decrease in the water-splitting voltage that occurs with increasing temperature. Unlike other processes, this uses the complete solar spectrum to increase solar efficiency, i.e., both the visible light to drive photovoltaics and also solar–thermal radiation that would normally be wasted as sub-bandgap energy. The hybrid process combines photovoltaics with the excess sub-bandgap heat to deliver efficient, elevated-temperature, solar water electrolysis to produce hydrogen. High-temperature electrolysis components are available, and solar concentration can provide the high temperature and diminish the surface area of the components for solar conversion to electrical energy.Fundamental thermodynamics are used to show that solar-to-hydrogen conversion efficiencies of about 50% are accessible over a wide range of insolation, temperature, pressure, and photovoltaic band-gap condition.