Helena Gajbert, Energy and Building Design, Lund University, Sweden Hakan Hakansson, Energy and Building Design, Lund University, Sweden Bjorn Karlsson, Energy and Building Design, Lund University, Sweden

By indoor measurements with steady surrounding conditions evaluations of concentrating solar collectors could be facilitated and made more systematic. In this article, a method is described of how indoor measurements of incidence angular dependence of concentrating collectors can be performed by using a large solar simulator providing nearly parallel light. The problem of spatial non-uniform irradiation from the described simulator is taken into account and compensated for by measurements of the total irradiation by several photodiodes placed in front of the test area.

Background

Concentrating solar collectors have a potential to be cost efficient in comparison to flat plate collectors due to lower investment costs (Adsten, 2002). The ability of evaluating solar collectors indoors provides independence of unwanted climate changes and facilitates the repetitiveness of the experiments. In order to enable indoor evaluation of concentrating solar collectors, a light source with parallel light is required. These kinds of light sources are not common, hence indoor evaluations are rare. A solar simulator providing nearly parallel light, and adjustable for solar angles is in use at Energy and Building Design at Lund Institute of Technology. The distribution of irradiated light from the simulator is however rather uneven. Hence, some results from previously performed evaluations of concentrating solar collectors have been somewhat difficult to interpret. (Gajbert et al., 2003)

The objective of this work is to develop a method to compensate for the non-uniform light distribution and the movements of the light pattern while using the solar simulator. The aim is to improve evaluations of incidence angle dependence of concentrating solar collectors using the simulator.

A method that serves this purpose has been developed and is presented in this article. The idea is to estimate the total irradiance on the test area, based on continuous measurements with a number of photodiodes placed on the glazed surface of the solar collectors. By using this method, two different types of concentrating collectors with limited acceptance angles have been evaluated with respect to incidence angle dependence of the zero-loss efficiency and the results are presented and discussed in this article. Another method which assumes that the irradiance on the collector is proportional to the cosine of the angle of incidence is also tested. The results of these two methods are presented and discussed here.