Energy and Exergy Performance Comparison of Three Different Solar Cookers Using Different Loads

Abstract

AbstractThe aim of the study is to evaluate the energetic and exergetic thermal performance parameters of three different domestic solar cookers in Mahikeng, South Africa. The three domestic solar cookers evaluated are a parabolic dish solar cooker, a box solar cooker with a reflector and a box solar cooker without a reflector. The three cookers are compared experimentally with water heating experiments using 1.0, 1.5, 2.0, 2.5 and 3.0 kg loads on different days. Higher average energy and exergy rates are obtained with the parabolic dish solar cooker. The water heating load seems to have a very small effect on the average energy and exergy rates of the solar box cookers. The parabolic dish solar cooker has the lowest average energy efficiencies at lower loads. At higher loads, the energy efficiencies of the parabolic dish solar cooker increase to be higher than those of the box cooker without a reflector. The average exergy efficiency of the parabolic dish solar cooker increases with the load. The solar box cooker with a reflector shows the highest average energy efficiency values which increase with the load. The energy efficiency values for the solar box cooker with the reflector increase from around 0.25 to around 0.52 with an increase in the load from 1.0 kg to 3.0 kg. The corresponding energy efficiencies of the solar box cooker without the reflector and the parabolic dish cooker increase from 0.11 to 0.18, and 0.08 to 0.28, respectively. The exergy efficiencies of the box cooker with a reflector and the box cooker without a reflector fluctuate up and down slightly at mean values of 0.02 and 0.008, respectively, with an increase of the load. On the other hand, the parabolic dish solar cooker shows an increase in the exergy efficiency from 0.007 to 0.03 with an increase in the load. The solar box cooker without a reflector shows the poorest results in all thermal performance parameters evaluated. The greatest cooking potential in terms of the cooking speed is shown by the parabolic dish solar cooker, but when varying ambient conditions are considered then the box cooker with a reflector shows the best overall thermal performance.KeywordsBox solar cookerEnergy and exergyParabolic dish solar cookerThermal performance