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Amount of solar radiation absorbed by trough collectors with nonimaging optics

Solar collectors using non-imaging mirror troughs (e.g. CPC-troughs) significantly alter the angular and spatial distribution of incident radiation from the aperture to the absorber surface. For flat plate collectors the transmission of transparent covers (including honeycomb transparent insulation materials) can be modelled with one incidence angle modifier symmetrical to the collector's normal. After multiple reflections in a mirror trough however, this symmetry is not maintained and a more complex treatment is required. For three examples of mirror troughs, the angular distribution of gained solar radiation was calculated using a ray- tracing program, taking into account the angular dependence of the transmission of a cover and of the absorptance of a selective coating. The solar radiation at the aperture was modelled using the continuous diffuse radiation model of A. Brunger with radiation data from Freiburg.