Trapping light escaping from the edges of the optical element in a Concentrating Photovoltaic system

Abstract The encapsulant is an important element used for mechanical bonding and optical coupling between the concentrator and the solar cell in a typical concentrating photovoltaic system. In this work we explain the concept of trapping the light escaping through the optical concentrator – encapsulant interface. Understanding how the losses incur is important for the development of concentrating photovoltaic systems. A case study is performed on a 3D Cross Compound Parabolic Concentrator (3DCCPC) based low concentrating photovoltaic system. Detailed optical analysis is presented quantifying the losses based on the thickness of the encapsulant spillage. Simulation results show that the optical efficiency drops from 84.5% to 55.6% whilst increase in the encapsulant spillage thickness from 0.1 mm to 3 mm. Use of reflective film is made along the bottom edges of the concentrator in order to make the interface region optically inactive to carry out refraction and trap the escaping light. Modelling shows that the optical losses can be completely managed by the use of the reflective film. Experiments are carried out by building a prototype in order to demonstrate the concept and validate the results. The short circuit current is found to increase by a maximum of 8.5%. A maximum power ratio of 2.73 is observed at an incidence angle of 10° for the system using the reflective film compared to 2.56 without the reflective film.