A NUMERICAL APPROACH TO OHMIC LOSSES ASSESSMENT IN CONCENTRATING PHOTOVOLTAIC SYSTEMS

It is well known that concentrator solar cells operating under concentration experience a number of physical effects which affect their performances. In particular, ohmic losses can determine a noticeable performance worsening of concentrator solar cells. The goal of this dissertation is to develop a distributed electrical model of solar cell in order to simulate the operation of concentrator solar cells in a number of working conditions characteristic of Concentrating Photovoltaic (CPV) systems, such as uneven illumination profiles with arbitrary spectral distributions. To this end a mixed optical-electrical simulation tool has been developed in order to assess the performances of a typical concentrator solar cell in the case of illumination provided by different kinds of concentrators; in particular a Fresnel lens, a parabolic mirror and a freeform mirror have been considered and compared. At high concentration factors front contact grid pattern has a key role in extracting photogenerated charges, and hence it is another factor that can strongly affect the cell performances; for this reason the above mentioned distributed electrical model has also been applied to the assessment of ohmic losses impact on concentrator silicon solar cells performances in the presence of different kinds of front contact grid patterns. In particular, a comb-like geometry, a square-like geometry and a novel fractal autosimilar geometry have been simulated and compared. Another aspect investigated in this dissertation is the formation of voids in the solder joint region, during soldering process of concentrator solar cells to Metal Core Printed Circuit Boards (MC-PCB). Some commercially available silicon solar cells have been soldered in such a way that a great number of voids have arisen and their distribution has been revealed by X-ray inspection. Electrical and thermal behaviour of one of the cells has been assessed by a joint thermal-electrical simulation tool. In this thesis electrical, optical and thermal simulations have been performed by means of ORCAD PSPICE software, ZEMAX software and ADINA 8.7 software, respectively.