Development and performance analysis of a parabolic dish solar concentrator integrated with a heat storage block

Abstract

Solar irradiance received on the earth’s surface is highly intermittent. This affects the availability of solar energy for cooking especially with parabolic dish solar cookers which rely on beam solar irradiance. In this study, a parabolic dish solar concentrator (PDSC) with a dish of diameter 1.50m, aperture area 1.77 m2 and focal length 0.60m was designed, constructed using materials available in Uganda, and was tested by boiling water and cooking some food stuffs. A heat storage block made of Aluminium was incorporated with PDSC to store energy for use during low irradiance periods. The experimental results show that the standardized cooking power at a temperature difference of 50 0C between ambient air and cooking vessel water temperatures (Tw − Ta ) was 169.87W, the optical efficiency factor was 0.327, the heat loss factor per concentration ratio was 2.353 Wm-2 K-1 and Cooker Opto-thermal ratio was 0.139. It took 20 minutes to boil two litres of water on a clear day when the beam solar irradiance was between 1046 and 1088 Wm-2 whereas under a relatively cloudy day with beam solar irradiance between 542 and 1020 Wm -2 averaged at 728 Wm-2, it took 52 minutes. The HSB was able to store 1126.2 kJ in 1 hour 36 minutes under a relatively clear sky of average beam solar irradiance of 896 Wm-2. When the HSB was charged to 174.4 0C, it heated 1.5 litres of water from 29 to 81.2 0C in 36 minutes yet the solar irradiance during this period was too low and highly fluctuating (average of 428.8 Wm-2 and a standard deviation of 295.4 Wm-2 ) to cause any water temperature change when there is no HSB. This study shows that incorporating PDSC with a heat storage block stabilizes energy for cooking under intermittent solar irradiance.