Phase change materials for energy storage in solar box cooker

Abstract

The use of solar energy for cooking offers an alternative source of energy to the high cost of petroleum products and the diminishing wood fuel products for cooking and heating applications. Kenya is located on the equator and receives a daily insolation of 4-6kWh/m2 hence most areas can be considered as having high potential for solar energy utilization. Most of the solar cooker designs do not have thermal storage systems and can only be used for cooking when there is sunshine and cannot be used during cloudy weather or in the evening. The aim of this study was to design and assess the performance of a double reflector solar box cooker with an energy storage unit. The use of phase change materials (PCMs) as a technique of storing energy was used to overcome the time mismatch between solar availability and demand. The PCM used is acetanilide with a melting point ranging from 113°C to 116 °C. The box cooker was designed so that the length to width ratio for the reflector and the glass window was 4:1. This eliminated the azimuth tracking towards the sun. Three sets of experiments were carried out at the School of Engineering and Technology Demonstration Centre, Kenyatta University. The first without loading the cooking pot of the cooker, the second with water as the cooking load and the third with different actual cooking loads. The measured parameters included, the solar radiation, ambient air temperature, temperatures of the different components of the solar cooker, load temperature and wind speed. The data values were read and recorded by use of a data logger at regular intervals of 10 minutes. Data analysis was done using statistical measures. An average stagnation temperature of 85.9 ± 24.0 °C and 82.7 ± 24.3 °C was achieved in the two pots. The average solar radiation was 637.1 ± 212.0 W/m2. The cooking power tests achieved a coefficient of performance of 0.754. The results showed that the double reflector solar cooker with energy storage can be used to cook meals throughout the day and in the evening. Noon cooking does not affect evening cooking. The adoption of this study will be beneficial to Kenyans as it will increase the acceptability of the solar cookers hence reduce the consumption of wood fuel and petroleum products. This will reduce the rate of depletion of wood resources, and provide a clean environment devoid of hazardous emissions associated with wood and fossil fuel combustion. Keywords - Clean environment, Energy storage, Phase change material, Solar box cooker.