Comparison of energy and exergy efficiency for solar box and parabolic cookers

The present work deals with evaluating the energy end exergy efficiency of box-type (SBC) and parabolic-type solar cookers (SPC). Energy and exergy analyses were applied to solar cookers (SCs). Thermodynamic considerations required to develop rational and meaningful methodologies for the evaluation and comparison of the efficiency of the SCs were defined. It was found that the average daily water temperature from 10:00 to 14:00 solar time was 344.4 and 333 K in the SBC and SPC, respectively. The average daily temperature difference in the SBC and SPC was 42.97 and 31.56 K, respectively. The results of this study show that the difference between the results of energy and exergy analyses is significant. The energy output of the SBC ranged from 8.2 to 60.2 W, whereas it was varied between 20.9 and 73.5 W for the SPC for the same time interval. The exergy output for the SBC ranged from 1.4 to 6.1 W, whereas it was in the range 2.9-6.6 W for the SPC. A linear and polynomial regression of the plotted points was used to find the relationships between energy/exergy outputs, and efficiencies and temperature difference. The energy and exergy outputs at a temperature difference of 50 K for the SBC and SPC were estimated to be 26.5 and 124.5 W and 5.23 and 12.02 W, respectively. The energy and exergy efficiency for the SBC and SPC was in the range 3.05-35.2%, 0.58-3.52% and 2.79-15.65%, 0.4-1.25% during the experimental period.