Hybrid sensible-latent heat thermal energy storage using natural stones to enhance heat transfer: Energy, exergy, and economic analysis

Latent heat thermal energy storage addresses the mismatch between energy supply and demand; however, phase change materials (PCM) commonly have the issue of low thermal conductivity. Natural stones, as low-cost and environmentally friendly sensible heat storage media, are used to enhance the heat transfer of the PCM in the current study. Different stone types, sizes, and filling heights are tested, and a comprehensive energy, exergy, and economic analysis is performed. Results indicate that granite has the best heat transfer enhancement performance owing to superior thermal diffusivity, which accelerates the melting by 108 % (initial temperature: 23 °C; heating temperature: 75 °C). Basalt with high specific heat contributes to the large energy capacity. The total exergy is hardly influenced by the stone size ranging from 15 mm to 40 mm, where the minimum is only 5.1 % lower than the maximum. The exergy storage rate benefits from stones surrounding the inner tube and is increased by 246 % with a filling height of 112.0 mm. The 40 mm-sized stones are the most cost-effective in the current testing conditions, and a 560 % increase in the economy is achieved. This study demonstrates a high-performance, low-cost, environmentally friendly energy storage configuration and provides comprehensive information for potential energy recovery applications.