Energy and exergetic analysis of applying solar cascade utilization to an artificial photosynthesis energy supply system

Abstract

Although artificial photosynthesis can produce hydrocarbon fuels and reduce carbon emissions, current implementations cannot optimally utilize the solar spectrum and thus are inefficient. This research proposes a new hybrid energy system, which begins by applying the photovoltaic/thermal panel to simultaneously generate higher-grade electricity and lower-grade heat. Then, the electricity is supplied to the carbon dioxide reduction reactor, and the heat is supplied to carbon capture by adsorption and optionally the absorption chiller. By coupling the carbon capture and reduction reaction via the photovoltaic/thermal panel, efficient cascade utilization to generate solar fuels from a single solar energy source is achieved. The energy and exergy models that couple the individual devices are developed and the effects of photovoltaic conversion efficiency and the distribution of heat between the carbon capture by adsorption and absorption chiller are examined. Results show that the optimal power/heat ratio by the photovoltaic/thermal system to gain a proper mass balance characteristic is above 1.5 to yield 3.5 kg/m2 of methanol at 10 solar concentrations. Furthermore, carbon capture from the animal farm can contribute an additional 5% exergy efficiency over atmospheric air. Overall, maximizing the photovoltaic electrical efficiency is key to maximizing the system’s energy and exergy efficiencies.