CPV optics: optical design and tests

In recent years Concentrating Solar Power (CSP) and in particular Concentrating PhotoVoltaics (CPV) have undergone remarkable technical improvements. New photovoltaic technologies have allowed reaching high levels of collection efficiencies and the introduction of collecting optical systems has reduced the area of the PV cell. As a consequence, CPV systems have become a commercial product, giving rise to extensive industrial experimentation on concentrating photovoltaics and on new PV cells. These innovative CPV technologies require a high level of solar light concentration (HCPV). The chapter proposes different collectors for the exploitation of solar light using CPV systems. Optical systems for CPV have been developed, realised and tested. They are designed to be realised in PolyMethyl MetaAcrylate (PMMA) and to be coupled to a circular PV cell 2mm in diameter with a concentration ratio exceeding 500. The initial phase of the work consists of a ray tracing analysis aimed to control and optimise optical parameters and performances of collectors. The second step is the realisation of some samples following the optimised optical project. The third phase is represented by the optical tests performed on the realised optics to compare real features with nominal characteristics and performances. The first phase begins with selecting optical configuration, collector dimensions, focal distance and concentration ratio, which are usually chosen in agreement with the requirements of each specific CPV application. Starting from these optical features, several optical projects are simulated and optimised. A successive analysis examines the optical characteristics that are significant for the CPV application. Collection efficiency, image size and image uniformity are important aspects to be considered in the case of light concentration on photovoltaic cells. The result of this first step is to define an optical project for the solar collector, which is the starting element for the second phase. Then the manufacturers realise the optical components on the base of the optical prescriptions, consisting in surface curvatures, dimensions, material and design details. Finally, in the third phase, a series of measurements assess the optical features corresponding to each collector sample. The purpose of these tests is to compare optical characteristics and performances measured on the realised optics to the corresponding values estimated by the ray tracing simulations. Test measurements concern the optical features essential for the CPV application, such as collection efficiency and image light distribution.