Characterization of a Test Site for the Measuring of the Focal Point of Reflective Optical Elements for Concentrator Photovoltaic

TL;DR

This paper characterizes a specialized optical test site for measuring the focal point of reflective optical elements used in concentrator photovoltaics, focusing on component behavior and calibration to optimize mirror quality assessment.

Contribution

It provides a detailed analysis and modeling of the test site's components, including empirical calibration of the diffuser film for accurate measurements.

Findings

Successful modeling of most test site components

Empirical calibration improves measurement accuracy

Identification of diffuser film's complex behavior

Abstract

In order to achieve a large deployment of renewable energies, the electricity production costs have to be as low as possible. Many different technologies have been proposed to achieve the best efficiency to cost ratio. One of those is concentrating photovoltaics (CPV) which takes advantage of the high efficiency of multi-junction cells while limiting the costs by reducing the size of the cell and concentrating the direct irradiance with a cheaper optical element. Next to the widely used Fresnel lenses concave mirrors could be of interest as concentrator optic. As for the whole module those optics have to minimize losses and production costs at once. Measuring scattering and slope errors of the mirrors is of great importance to achieve an optimal design and production process. Therefore an optical test site doing so by observing the 2D irradiance distribution in the focal point has been built at the Fraunhofer ISE. The aim of this thesis is to characterize this test site. Therefore the behavior of the different components (camera, objective, mirrors, glass plate, light source and diffuser film) as well as of the whole test site have been measured and modeled. While most parts of the test site could be modeled in a satisfactory way, the diffuser film still isn't fully understood. Therefore an empirical calibration has been done.