Collaboration to the PHOCUS project

During the development of the PHOCUS project INOA has worked for ENEA to study, test and apply a procedure to realise the optical characterization of solar concentrators designed and optimized for coupling with photovoltaic (PV) cells. The developed procedure examines and compares samples of prismatic lenses and Fresnel lenses, made with different manufacturing processes and various materials.

The optical characterization of the lenses had as its aim the verification of the correspondence between the behaviour of the lens realized and the design characteristics of the lens itself. To concentrate light on the PV cell is necessary that the image produced from the collector respects some features regarding the shape and distribution of light intensity. The first fundamental characteristic is to have an image with shape and dimensions corresponding to the size of the PV cell, hence in this case it was requested a spot of square shape. The second feature is to achieve maximum efficiency of collection, that is, to focus light as possible within the sensitive area of the cell. The third characteristic concerns the maintenance of the uniformity of the intensity of the light on the same sensitive area. The solar cell achieves a good conversion efficiency only if it is uniformly illuminated.

The used instrumentation and measurement techniques have led to examine the total collection efficiency and the energy distribution in the image plane of the lens. A specific study has been devoted to the measure of the uniformity of the image, even separating the contributions of the different regions of the lens.

The methodology for the optical characterization of solar collectors consists of the following measures:

1. Test of the total collection efficiency of the lens.
2. Analysis of contributions to the image due to the different regions of the lens.
3. Energy distribution in the image plane.