Thermal analysis of a mini solar pond of small surface area while extracting heat from lower convective layer

Abstract

Solar energy is major renewable energy resource which can potentially fulfill 100% energy demand of the world while releasing no polluting agents to the atmosphere in contrast to the conventional fossil fuels. However, due to its intermittent nature, solar energy requires effective storage of energy for utilizing during the night and cloudy weather. A solar pond is a promising solution because it has its own energy storage which is suitable for low temperature application like building heating and cooling. This paper presents a thermal analysis of a salt gradient solar pond while extracting heat from the lower convective zone. A mathematical model of surface area is developed. Efficiency analysis is performed numerically using a MATLAB code for steady temperature difference of 30°C as well as 20°C across the gradient layer for three different pond sizes of depths 1.5 m, 1.0 m, and 0.5 m. The thermal efficiency of first pond of 1.5 m depth varies from around 21% in summer to 11% in winter. Thermal efficiency of solar pond drops significantly by reducing its size and non-convective zone thickness. Annual average efficiencies are 21%, 19%, and 9.5% for the three ponds of 1.5 m, 1.0 m, and 0.5 m depths, respectively. So it is recommended to prefer a pond of 1.5 m over others. However, the efficiency of smaller the pond can be significantly improved by compromising on quality the of thermal energy, efficiency of 0.5 m pond rises to 17% when operating at temperature just 20°C above ambient, compared with 9.5% for 30°C above ambient. Solar pond therefore proves to be suitable for effectively utilizing solar energy and can present an effective solution for low temperature energy needs like space heating.