A mini solar thermal collector integrated with a new thermal energy storage as a decentralised energy solution: An experimental study

Solar thermal collectors are highly effective decentralised energy solutions because they convert sunlight directly into thermal energy (heating/cooling) at the point of use, reducing reliance on centralised grids and fossil fuels. They are efficient, sustainable, and ideal for decentralised applications. This work focuses on utilising a new heat-storage medium (volcanic rock) within a solar thermal collector, i.e., a hot box-cooker (SHBC), to perform solar cooking under the climatic conditions of Uttar Pradesh, India. The SHBC was studied across three different seasons—summer, rainy, and winter in India—to assess its feasibility and enhance its thermal performance using volcanic rock (granules), which was experimentally studied in an SHBC. These granules were filled beneath the cooking tray, which allows the stored solar radiant heat to increase significantly, leading to improved heat transfer and longer heat retention within the cooker. All performance parameters were carefully evaluated, demonstrating that the environment significantly influences the SHBC's cooking performance. Consequently, the optimum results were achieved in summer, with a maximum thermal efficiency of about 40.10%, a heat transfer coefficient of 31.9 W/m 2 . K, a heat loss coefficient of about 5.7 W/m 2 .K, a primary value of the Cooker Opto-Thermal-Ratio of 0.121 (m 2o C)/W, and the First figure of merit of around 0.13. The SHBC was specifically designed for a small Indian family of about 4–5 members from rural Moradabad and nearby Indian regions. The cooker can prepare at least four meals per day in summer and two meals on sunny winter days. The modified cooker costs roughly $68, with a payback period of about 2.95 years.