Comparative Thermal Performance Evaluation of Solar Box Cookers Insulated with Kapok Fiber and Sodom Apple Fiber Materials

Reliance on biomass fuels in developing countries has led to environmental degradation and health challenges, highlighting the need for affordable clean cooking alternatives. This study compares the thermal performance of solar box cookers insulated with Kapok fiber and Sodom apple (Calotropis procera) fiber. Two identical cookers were tested using Bureau of Indian Standards (BIS IS 13429:2000) procedures under no-load and water-heating conditions. Performance was evaluated using absorber temperature profiles, first figure of merit (F₁), and second figure of merit (F₂). Both systems showed nearly identical performance, with peak absorber temperatures of 145.7 °C (Kapok) and 146.6 °C (Sodom apple fiber). F₁ values (0.123–0.124 m²K/W) confirmed Grade A performance, while F₂ values (0.056–0.057) indicated similar heat transfer efficiency. Statistical analysis (p > 0.05) showed no significant differences between the cookers. Results confirm that Sodom apple fiber performs comparably to Kapok fiber and all locally sourced insulating materials represents a viable, low-cost, and sustainable insulation material for solar box cookers.