Performance study on a novel hybrid solar gradient utilization system for combined photocatalytic oxidation technology and photovoltaic/thermal technology

A novel hybrid solar photocatalytic, photovoltaic and thermal recovery system that meets the domestic demands for air purification, electricity generation, space heating and hot water supply in one integrated is proposed (PC-PV/TAW). The photocatalytic module uses ultraviolet part to drive photocatalytic degradation of indoor pollutants, and the photovoltaic/thermal module absorbs visible and infrared parts to generate electricity, warm air and hot water. In this article, three photocatalytic-glass modules with different TiO2 coating density are prepared and the effect of TiO2 coating density on the performance of electrical, thermal and formaldehyde degradation for PC-PV/TAW system is investigated. In addition, comparisons of PC-PV/TAW system with two conventional systems of photovoltaic/thermal water system (PV/TW) and photovoltaic/thermal air and water system (PV/TAW) are conducted. Finally, the associated losses of PC-PV/TAW system and two conventional PV/T systems are analyzed. Results are as follows: (1) PC-PV/TAW system with TiO2 coating density of 1.86 g/m2 behaves the best thermal and electrical performance while a little reduction of formaldehyde degradation performance among three PC-PV/TAW systems; (2) The electrical efficiency of PC-PV/TAW system approaches 0.174 both considering generated electricity by PV modules and saving electricity by purifying air; (3) The overall thermal and electrical efficiency of PC-PV/TAW, PV/TAW and PV/TW system is 0.644, 0.696 and 0.677, respectively, while PC-PV/TAW system can generate total volume of fresh air of 248.040 m3/(m2·day); (4) The loss analyses show the solar spectral characteristics of TiO2 coating is the key to system performance of PC-PV/TAW system.