Optical and Thermal Performance of Load Adapted Solar Collectors

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This thesis is part of a research project about Load Adapted Collectors (LAC) for high latitudes at the Solar Energy Research Center (SERC) in Borlänge. Load adapted collectors have been studied regarding their optical and thermal performance. The aim of this kind of collector is to reduce the mismatch between solar radiation and heating load for locations with high latitudes like Sweden. Using the LAC in solar combisystems for domestic hot water and heating may also eliminate overheating problems in the summer months. Internal reflectors are used for the collectors to obtain a lower output in the summer and a higher gain in spring, autumn and winter. In order to keep the construction as simple as possible only flat cylindrical surfaces have been applied for the reflectors. Within the research project another thesis work has been accomplished by Fars Mustafa, which deals with theoretical models to optimise the geometry of the LAC. Based on his results two collector prototypes have been built and tested outdoors. The evaluation showed that the determined angular dependent optical efficiency suits with the values obtained from the theoretical analysis. Deviations for the first collector prototype can be explained mainly by optical imperfections of the reflector. The first prototype has a sharper pronounced angular dependency than the second model. The two prototypes show a similar thermal performance. Both have a U-value of about 2.6 W/m2K for a ?T=50K, which is an improvement of about 1.2 W/m2K in comparison with former prototypes. The second tested prototype uses a half sized bi-facial absorber, which has not result in lower heat losses. However, the application of the 70 mm wide absorber has the advantage of a slimmer collector and simplifies the integration into roofs. One year simulations for a test system using the parameter obtained from the measurements have been carried out. From the results can be seen that both col...