An analytical estimation of salt concentration in the upper and lower convective zones of a salinity gradient solar pond with either a pond with vertical walls or trapezoidal cross section

Abstract

Renewables offer the best opportunity to reduce greenhouse gases and introduce sustainable and desirable solutions to the world’s increasing demand for energy. Solar ponds are a simple, low-priced and efficient way to collect and store incident solar radiation; they have enormous capacity and huge unrealised potential. The most effective and widely-used type is the salinity gradient solar pond (SGSP), which can provide long-term storage, large capacity, and sufficient year-round power for a wide range of domestic, industrial and commercial purposes. It is essential to understand the best forms of construction and maintenance, including how to overcome the most significant challenge, that of establishing the different layers of water with their varying levels of saline concentration, as well as how to maintain these levels for optimal performance. This study investigates how to predict variations in salt concentrations over the pond’s lifetime, in order to maintain maximum performance. The paper derives analytical formulae to calculate how concentrations in the upper and lower convective zones (UCZ and LCZ) change over time. It also explores the different responses of ponds with vertical walls and inclined walls. The computed concentrations were compared with actual measurements from a small experimental pond, which had a surface area of 1m2 and a total depth of 1m, comprising UCZ, non-convective zone (NCZ) and LCZ with depths of 0.1, 0.5, and 0.4m respectively. The results were also compared with the results of previous experiments from established ponds. An acceptable agreement was achieved. The results illustrated that the derived formulae can be used to estimate salt concentrations in the UCZ and LCZ. The outcomes also show that the inclination of the walls affects concentration levels in the UCZ, while its impact on the LCZ concentration is slight. The findings of this study could form the basis of future research, which could investigate other factors affecting salt concentration in the layers of a SGSP, such as wind speed, temperature and the timing of salt injections to the LCZ.