| More than80%of the solar radiation falling on photovoltaic (PV) cells is not converted toelectricity, but either reflected or converted to thermal energy. This leads to an increase in thePV cell’s working temperature and consequently, a drop of electricity conversion efficiency. Inview of this, hybrid photovoltaic and thermal (PV/T) collectors are introduced tosimultaneously generate electricity and thermal power. The most common design has the solarcells fixed on top of the absorber of a flat-plate solar thermal collector. Natural circulationmeans that water flows depending on the thermosyphon head due to the buoyancy force,which is due to the change in density of water caused by water temperature rise in the solarcollector.On the basis of previous research and heat transfer mode of PV/T, three configurations ofhybrid photovoltaic and thermal solar flat-plate collector are developed: absorber combinedsolar cells in PV/T (ACS PV/T), cover combined solar cells in PV/T (CCS PV/T) andabsorber combined solar cells without air layer in PV/T (ACSWITHOUTAL PV/T). Firstly,three PV/T are studied in Fluent with great emphasis on solar cell covering factor and theresults show that as the covering factor rises, the performance of photovoltaic of CCS dropssharply. In addition, temperature distribution of solar cells, cover and absorber is presented.Experimental rig is also built and two sets of PV/T are tested. First set compares the ACSand CCS with the traditional solar collector and PV panel while all PV modules have the samecovering factor(0.55), which indicates that ACS has the highest primary-energy savingefficiency but lowest electricity conversion efficiency while the traditional solar collector andPV panel has the best performance of thermal and photovoltaic respectively. CCS’sphotovoltaic performance is also found to be satisfactory which is just a little poorer than thetraditional PV panel. Second set includes three PV/T: ACS and ACSWITHOUTAL with highcovering factor(0.92), CCS PV/T with low covering factor(0.37). The experiments show thatdue to amazing photovoltaic performance, the primary-energy saving efficiency ofACSWITHOUTAL PV/T is as high as ACS PV/T which has the same high covering factorand the thermal performance of CCS PV/T with low covering factor is as good as ACS PV/T with high covering factor.In order to study the performance of PV/T in depth, the dynamic modes of threeconfigurations of PV/T are developed, and first two of them are validated by comparing theexperimental results of water temperatures in tank and energy gains throughout a day with thesimulation results based on the actual daily weather data acquired during the experiment. Verygood agreement between the two sets of results was found. Then the same validated modelsand weather data sets are used to carry out the sensitivity analysis on the effect of some keycollector-design parameters: solar cell covering factor, the height of air layer, tank volume andabsorptivity of the absorber. It is found that the same conclusions with previous CFD andexperimental study can be obtained on the effect of solar covering factor. It is also suggestedthat air layer should exceeds15mm and big capacity of tank is chosen to get better thermalperformance in summer. The rise of absorptivity of absorber can promote both photovoltaicand thermal efficiency. |
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