Measurement of radiation distribution on the absorber in an asymmetric CPC collector |
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| Authors: | M. Adsten, B. Hellstr m,B. Karlsson |
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| Affiliation: | a The Ångström Laboratory, Uppsala University, P.O. Box 534, S-751 21, Uppsala, Sweden;b Energy and Building Design, Department of Construction and Architecture, Institute of Technology, Lund University, P.O. Box 118, S-221 00, Lund, Sweden;c Vattenfall Utveckling AB, S-814 26, Älvkarleby, Sweden |
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| Abstract: | A method to estimate the annual collected energy and the annual average optical efficiency factor is suggested. The radiation distribution on the absorber of an asymmetric CPC collector with a flat bi-facial absorber is measured for three different absorber mounting angles using a photo diode. The annual optical efficiency factors and a relative measure of the annual collected energy are determined for collectors with the absorber fin thickness 0.5 and 1 mm, and for a collector with a teflon convection suppression film mounted around the absorber. With the local optical efficiency factors and the annual incident solar energy distribution considered, the analysis indicates that the energy gain for a mounting angle of 20° is higher than for a collector with 65° absorber mounting angle. The annual collected energy is increased with 6–8% if the absorber fin thickness is increased from 0.5 to 1 mm. The annual average optical efficiency factor is relatively independent of the absorber mounting angle. It was found to be 0.87–0.88 for a collector with a 0.5 mm thick absorber fin and 0.92 for a collector with a 1 mm thick absorber fin or for a collector with 0.5 mm thick absorber fin with a teflon convection suppression film added. The low annual average optical efficiency factor is not caused by the uneven irradiance distribution but by the relatively high UL-values. |
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