Investigation of an innovative PV/T-ORC system using amorphous silicon cells and evacuated flat plate solar collectors

Abstract

Solar-driven organic Rankine cycle (s-ORC) power generation is a promising technology with thermal storage for flexible operation to meet domestic variable electricity demand. A satisfactory efficiency of this technology can be obtained only at medium-to-high temperature, for which conventional flat plate and evacuated tube solar collectors are not suitable while solar concentrators cannot efficiently utilize diffuse solar radiation. Evacuated flat plate (EFP) collectors have recently been developed for efficient solar heat collection in the temperature range from 100 to 200°C, suitable for the ORC system. At present, the cost of EFP collectors is relatively high and will lead to a long payback period of the s-ORC system. To increase the annual power yield and reduce the payback time, inexpensive amorphous silicon (a-Si) solar cells are proposed to be integrated into the EFP collectors. It is the first time to put forward such photovoltaics/thermal (PV/T) design combining a-Si cells and EFP collectors. Compared with polycrystalline silicon cells (poly-Si), a-Si cells may have a higher electrical efficiency at a higher operating temperature due to the thermal annealing effect and are expected to have a long lifetime without encapsulation in the vacuum environment provided by the EFP collectors. In this study, the a-Si PV/T-ORC system using EFP collectors is investigated. Transient performance analysis of a-Si PV/T-ORC is given for the weather data of two selected days. A comparison is also made with a stand-alone poly-Si PV system, poly-Si PV/T-ORC system and s-ORC system with EFP collectors alone, respectively. The results indicate that for a typical day in July, the a-Si PV/T-ORC system has the highest daily power output of 0.822 kWh/m2, 102.3% more than the s-ORC system, 23.8% more than the stand-alone poly-Si PV system and 12% more than the poly-Si PV/T-ORC system, respectively.