KomGen – Development of Next Generation Concentrator Modules

Characterization of Parabolic Reflectors for Concentrator PV

Duration: April 2010 - March 2014
Contracting Authority / Sponsors German Federal Ministry of Economic Affairs and Energy (BMWi)
© Fraunhofer ISE

Fig. 1: Diffuser plate in the focal plane of a parabolic reflector during a measurement.

© Fraunhofer ISE

Fig. 2: Schematic configuration of the measurement set-up.

© Fraunhofer ISE

Fig. 3: Measured spatial distribution of the radiation concentration in the focal plane of two parabolic reflectors.

Concentrator photovoltaics (CPV) uses tiny solar cells for electricity generation and a larger area with optics to collect and focus the sunlight. Parabolic reflectors are suitable optical components, as they do not suffer from chromatic aberration, in contrast to lenses. The distribution of the focussed sunlight over the solar cell is one decisive factor affecting the efficiency of the entire system. We determine this distribution in a newly developed measurement set-up and use it to predict the system performance. With this information, we can optimize the geometrical parameters of the parabolic reflector and its fabrication process, as well as carry out quality control.

CPV systems concentrate direct sunlight onto small solar cells, e. g. with parabolic reflectors. The optical properties of the reflectors are characterized in our newly developed measurement set-up. The measurement system measures the spatial distribution of the optical concentration over the focal plane of the parabolic reflector, where the solar cell would be located in a concentrator PV system. The measurement thus provides direct information on the spatial distribution of radiation over the cell in the real system.

As the focus of a parabolic reflector is located within its entrance aperture, a detector located there in the measurement system would obstruct the incident radiation. For this reason, we have installed a small diffuser plate there, which is imaged with the help of a light-deflecting mirror by a CCD camera mounted outside the entrance aperture (Fig. 2).

The difference between two parabolic reflectors, which were fabricated by different production processes, becomes clearly visible in the spatial light distributions determined with the measurement set-up. One reflector concentrates the light very well onto a central point (Fig. 3, left). The other reflector leads to a star-like distribution of the light in the focal plane (Fig. 3, right). The measurement results provide information about the influence of surface deviations on the power yield of the CPV system, and lead to valuable conclusions concerning further improvement of the optical concentrator system.

 

About the Project

At Fraunhofer ISE, we cover the entire development chain of concentrator photovoltaic systems (CPV), starting from solar cells or concentrator optics up to entire modules and systems, including the characterization of components and modules. In the course of the project “Development of Next Generation Concentrator Modules – KoMGen,” new concepts were developed for the CPV technology and evaluated in terms of both their technological as well as economical potential. The developed concepts form the basis for future CPV systems.

The article "Characterization of Parabolic Reflectors for the Concentrator PV" describes only one aspect of the entire project. Another part of the project focused on the "CPV Module Technology Based on Cassegrain Optics".