This report describes the research activities carried out by RSE, under the Electrical System Research (ESR) plan, ‘Concentrating Photovoltaic (CPV)’ project, with the aim of help reducing the costs of CPV technology, for it to be more competitive with other energy sources. In fact, CPV systems have advantages, such as the use of cells with a very small surface which reduces the use of semiconductor material, and the possibility of achieving high conversion efficiency and reducing the overall surface required for generation system installation; however, the international market for CPV technology is still limited by the cost of component production, which, although it has decreased in recent years, is still unable to be competitive with the costs of non-concentrating photovoltaics.

The research conducted by RSE during 2018, also in collaboration with national and international Research Institutes and Operators, allowed continuing the activity for the development and implementation of innovative technological solutions at all stages of the CPV technology chain. In particular: (1) new materials and processes were used for realising low-cost4-junction monolithic CPV cells (which are obtained by integrating ternary SiGeSn with III-V compounds) equipped with nano-structured, anti-reflective coatings, and diagnostic and characterisation systems were developed that are suitable for the new cell types; (2) innovative optical systemswere studied that can perform sun tracking with no need for moving mechanical parts and that are therefore also suitable for building-integrated solutions; (3) compact modules were optimized with innovative anti-fouling coatings and integrated sun pointing devices, alignment between mirrors and CPV cells was improved, new circuit solutions were applied inside the modules, and outdoor characterisation techniques for CPV modules were developed (carried out by RSE under this project and the related EU CPVMatch project); finally, (4) consistency was enhanced of thedatabase of sun direct and spectral radiations to which CPV generation systems are sensitive; this was obtained with data from national sites and satellite surveys integrated with mathematical models of the atmosphere.

The activities conducted in this project have enabled the experimental development of innovative low-cost techniques, so far only analysed in the literature, and especially, among others, themonolithic growth of 4-junction CPV cells, thus overcoming the challenge of using group IV compounds (SiGeSn) together with III-V compounds (GaAs, InGaP) in the same growth chamber (MOCVD).