Toward high-efficiency hybrid (electricity and heat) high concentration photovoltaic systems

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

Photovoltaic power generation is a growing renewable primary energy source, expected to assume a major role as we strive toward fossil fuel free energy production. However, the rather low photovoltaic efficiencies limit the conversion of solar radiation into useful power output. Hybrid systems extend the functionality of concentrating photovoltaics (CPV) from simply generating electricity, to providing simultaneously electricity and heat. The utilization of otherwise wasted heat significantly enhances the overall system efficiency and boosts the economic value of the generated power output. The system presented in this lecture is the outcome of collaborative research in my research group, with the IBM research lab in Zurich and the Fraunhofer Institute for solar energy systems in Freiburg, Germany. It consists of a scalable hybrid photovoltaic-thermal receiver package, cooled with an integrated high performance microchannel heat sink we initially developed and optimized for the efficient cooling of electronics. The package can be operated at elevated temperatures due to its overall low thermal resistance between solar cell and coolant. The effect of the harvested elevated coolant temperature on the photovoltaic efficiency is investigated. The higher-level available heat can be suitable for sophisticated thermal applications such as space heating, desalination or cooling (polygeneration approaches). A total hybrid conversion efficiency of solar radiation into useful power of 60% has been realized. The exergy content of the overall output power was increased by 50% through the exergy content of the extracted heat.