Integration of concentrated multi-junction solar cells with small-scale organic rankine cycle

Abstract

In this paper, concentrated photovoltaic system using multiple (four) multi-junction solar cells with a refractive system for a single point focus Fresnel lens was developed to achieve high performance in terms of optical efficiency, uniformity (Peak average ratio value) and compactness. Geometric concentration ratio, F-number, focal length and height of homogenizer were investigated showing that at Geometric concentration ratio of 400×, F-number of 1.12, focal length of 632.5 mm and height of homogenizer of 50 mm, the concentrated photovoltaic achieves an optical efficiency and Peak average ratio value of 79.6% and 1.52 respectively. Active cooling was simulated in order to ensure effective operation of the multi-junction solar cells (operating temperature < 110 °C) and to investigate the potential of exploiting the heat generated in the cells to operate an Organic Rankine Cycle to maximize the overall solar energy conversion efficiency. An Organic Rankine Cycle system with a target 1 kW power output is studied at different operating conditions and working fluid in order to be integrated with the Concentrated Photovoltaic Thermal system. Various configurations for integrating the Concentrated Photovoltaic Thermal units with the Organic Rankine Cycle working at various operating conditions and working fluids were investigated. Results showed that the integrated system with surface area of 16.8 m2, Organic Rankine Cycle system using R245fa can produce 6.17 kW of electricity with overall energy conversion efficiency of 46.57%. The developed system has the potential to provide the required electricity for buildings in Saudi Arabia which enjoys abundant solar radiation.