Design and Fabrication of a Parabolic Dish Solar Collector with a Thermal Compensator

Abstract

Solar energy is a free natural resource but its harvesting requires a high capital investment which prohibits its maximum exploitation. Moreover, most solar collectors do not give steady energy output due to fluctuating solar radiation caused by intermittent cloud cover. A Parabolic Dish Solar Collector (PDSC) with a thermal storage-recovery system has been developed to harness solar beam radiation and give steady energy output. The system was constructed using steel rods curved to obey the equation of a parabola then welded together with circular support rings. The inside curvature was filled with 3-ply wood to make a parabolic substrate. The substrate was then lined with reflective aluminium foil fitted with adhesive paste. The receiver was made of blackened copper bulb containing tin/lead alloy [60Sn40Pb, melting point = 172oC] engulfing a coiled copper tube carrying water as the heat transfer fluid. The alloy served as a Phase Change Material (PCM) for storing latent heat of fusion. The receiver was positioned at the focus of the parabolic reflector and was supported by a central antenna. The dish was mounted on an axle pivot driven by tension of a spring so as to track the sun along the equatorial latitude. The dish was inclined at an angle of 7.5o which was the solar declination during the season. During cloud cover the thermal storage material would lose sensible heat and latent heat of fusion to the flowing water, thus compensating for the absent solar energy. Efficiency, η of the system was determined by measuring the inlet and outlet temperature of water then calculation done as the ratio of heat gain per unit time against solar power intercepted by the aperture. The maximum efficiency with thermal compensator was 44.82% and minimum efficiency was 3.44% as compared to maximum efficiency of 11.6% and the minimum efficiency of 2.05% without thermal compensator. Thermal compensation factor, Cf was determined by simulating a cloudy condition by temporarily obstructing the dish aperture then measuring the energy output. On a clear day, the system was able to produce steam for various applications. The Solar Energy Device (SED) was found to give fairly stable and reliable energy loading during the solar harvesting period.