Optical control of sunlight concentrators

Optical collectors for sunlight concentration on small surfaces have been experimentally studied to evaluate their correspondence with the optical design. Measurement set-up and testing methodologies have been developed and adapted mainly to provide the optical characteristics that are fundamental for the concentration on small surfaces. The collectors are lenses of different type, with various shape and dimensions. They are optically designed to be realised in plastics and to be applied to concentrate the solar light on surfaces with dimensions of the order of 1 cm. Furthermore the optical control compares several samples of the same collector, realised with different production procedures and materials. The tests are aimed to verify the correspondence between the performance of the realised samples and the theoretical features of the designed collector. A specific study has been dedicated to the application to light concentration on PhotoVoltaic cells, whose requirements are a square-shaped image with uniform light distribution and maximum collection efficiency. The described instrumentation and measurement procedures examine total collection efficiency and energy distribution in the collector image plane. A particularly accurate and critical procedure performs the study of the image uniformity, separating the light contributions due the different collector regions. All measurements and in particular the "image contribution test" requires to adapt the testing set-up for each collector shape.