• Six robust solar cookers made of concrete were tested side by side. • Four were equipped with good-quality mirrors, while two had degraded mirrors. • An enhanced performance evaluation method was adopted. • Non linear curves for efficiency and performance data were determined. • Additional tests were conducted to assess the reproducibility of results. The Pucca solar cooker is a domestic funnel-type cooker, constructed of concrete and silvered glass mirrors. Its robust construction allows it to be kept outside permanently, in all weather conditions. However, its reflectors may gradually degrade over time, leading to diminished performance. To assess this issue, six Pucca cookers were tested side by side using a water load of 2 kg in each cooker. Two of the cookers had new mirrors, two had minimally degraded mirrors, and two had badly degraded mirrors. Non-linear efficiency curves were determined by a suitable enhanced evaluation method. Small differences were noted between the efficiency curves of the four cookers with the least degraded reflectors. By contrast, the points of maximum efficiency for the two cookers with badly degraded reflectors amounted to only about 70% of the value seen in the other cookers. The impact of this degradation on performance is illustrated by the figures predicted using the enhanced procedure, where the measured temperature data were fitted to a second-order polynomial with a time-dependent exponential term to derive nonlinear efficiency curves. The best performing cooker is expected to boil 2 kg of water in about three hours when the ambient temperature is 20 °C and the solar irradiance is 700 Wm −2 , and in only 1.4 h when the ambient temperature is 30 °C and solar irradiance is 1000 Wm −2 . The two cookers with badly degraded mirrors could not boil 2 kg of water at all under either of those conditions. The enhanced method is reliable.
Ruivo et al. (Wed,) studied this question.