Losses caused by dispersion of optical parameters and misalignments in PV concentrators

One factor greatly affecting the output power of a photovoltaic concentrator system and not found in conventional flat systems is optical mismatch, caused mainly by dispersion in the efficiencies of the optics and misalignments among collectors and modules. In these systems, there are many factors, besides the electrical performance of the PV modules, acting on the overall efficiency and thus on the power output: reflectivity and shape of the optics, cleanliness, misalignments, etc. They are less known than equivalent topics in flat arrays and usually the data come from medium-sized prototypes. Now we have the opportunity to study such factors on a big plant where components and the installation have been carried out by industry on a final user site. An analysis of the optical mismatch based on Gaussian distributions of the generated photocurrents will be presented in order to evaluate the power losses. A mathematical model is also proposed to calculate the main moments of the distribution from the experimental V-I curve under concentrated light. Besides, a novel study of the transmission curves of a photovoltaic concentrator has been carried out and will be described throughout the paper. The series/parallel connection of the modules can affect the transmission curve in different ways, depending on the array voltage, and thus this effect must be considered for the definition of the acceptance angle of the system. Copyright (c) 2005 John Wiley & Sons, Ltd.