Investigation of the Effective Transmittance-Absorptance Product of Solar Thermal Collectors Regarding Recent Improvements of Glazing and Absorber Spectral Properties
Abstract
A flat-plate collector in its simplest form consists of a flat heat exchanger with high absorptance for solar radiation (absorber) and a heat transport medium (air or water) to remove the heat from the heat exchanger. In this configuration, the absorber plate is directly exposed to surroundings. In order to reduce the thermal losses, not only are the back and sides thermally insulated with opaque materials (e.g. mineral wool), but a transparent cover can be placed between the absorber and the ambient air. On the one hand it reduces the amount of light reaching the absorber (optical losses due to the limited transmittance of the cover), but on the other hand, it reduces much of the convection losses from the front surface.