Performance analysis of A-Si photovoltaic/thermal system using optimized direct absorption collector

This paper extends our previous study on the photovoltaic/thermal system from the optimum optical properties of the working fluid to the system performance analysis. The system consists of a photovoltaic module using an a-Si solar cell and a thermal unit based on the direct absorption collector (DAC) concept. The system separately utilizes the solar radiation due to the advantages of the working fluid absorbing infrared radiation from 760 to 2000 nm and the transmitted visible light from 300 to 760 nm by the solar cell. In the system, the thermal unit absorbs 89% of the infrared radiation and transmits 84% of the visible light. The a-Si solar cell electrical efficiency varies slightly between 7.9% and 8.1% for various working fluid inflow temperatures. When reducing the mass flow rate of the working fluid, the thermal efficiency decreases; however, the outflow temperature of the working fluid reaches 77°C constant electrical efficiency about 8%. Moreover, the exergetic evaluation was adopted to quantitatively study the electrical energy and thermal energy conversion; the result confirms the existence of flow rate maximizing the total efficiency (optimum flow rate). Finally, when the incident solar irradiance is concentrated from 800 to 4000 W/m2 with the optimum flow rate 6 kg/h and working fluid inflow temperature 25°C, the total exergetic efficiency increases 5%, and the system generates 177°C high-grade heat, while the electrical efficiency is sacrificed slightly, around 1.3%.