An efficient ordered conversion system for hydrogen and electricity cogeneration driven by concentrated solar energy

Efficient utilization of full-spectrum solar photons is significant for improving the efficiency of solar energy conversion and thus alleviating energy shortage. In this work, a novel concentrated ordered conversion system based on a parabolic trough collector (PTC) that couples photocatalysis and Rankine cycle for hydrogen and electricity cogeneration to more efficiently use the full-spectrum solar energy is proposed. Higher-energy photons are absorbed by the photocatalytic layer for water splitting hydrogen production, and the remaining photons with lower energy that cannot excite electron-hole pairs (EHPs) are transmitted to the photocatalytic layer and converted into thermal energy to drive the Rankine cycle for electricity generation. Furthermore, the EHPs dissipated heat and absorber tube radiation heat loss can be reutilized in the photocatalytic layer to preheat the circulating water to increase the reaction temperature and solar evaporator inlet temperature to the designate temperature of 140 °C. Solar photocatalysis model and thermodynamic model are developed to simulate and analyze the system performance. Of the input solar energy, 10.34 % and 17.85 % are converted into hydrogen and electricity by photocatalysis and Rankine cycle processes, respectively. The total exergy efficiency increases from 23.51 % for the conventional PTC thermal power generation system to 28.49 % for the proposed system under the design condition. Then, the effects of the photocatalyst bandgap and temperature on the system exergy efficiency are analyzed, which indicates that when the photocatalyst bandgap increases, its operating temperature should be adjusted downward. The photocatalytic layer temperature is adjusted for corresponding maximum system exergy efficiency under different direct nominal irradiation (DNI) conditions, and it can maintain 140 °C of operation when DNI is greater than 240 W·m−2. This research provides a new approach to improve the efficiency and flexibility of full-spectrum solar utilization.