Improved thermal efficiency of salinity gradient solar pond by suppressing surface evaporation using an air layer

Salinity gradient solar ponds (SGSPs) provide a tremendous way to collect and store solar radiation as thermal energy, and can help meet the critical need for sustainable ways of producing fresh water. However, surface evaporation results in the loss of both water and heat. This study therefore theoretically investigates the effect on temperatures within an SGSP when its surface is covered with a layer of air encased in a nylon bag. An earlier SGSP model was slightly modified to add the air layer and to estimate the temperature distributions of the upper layer or the upper convective zone (UCZ) and the bottom layer or lower convective zone (LCZ). The results for a year-long period showed that adding the air cover increased the LCZ temperature to a maximum of 94°C in July, with a total average increase of about 9% over the uncovered pond. In the UCZ, temperatures showed an average increase of approximately 45%, reaching a maximum of 34°C. The temperature of the air layer was meanwhile found to be close to the ambient temperature and behaved identically. These findings invite future experimental and theoretical investigations into the use of air layers to prevent surface evaporation, thereby enhancing the efficiency of SGSPs as a source of clean energy.