The effect of a liquid cover on the thermal performance of a salinity gradient solar pond: An experimental study

Salinity Gradient Solar Ponds (SGSPs) offer the potential to capture and store solar energy for use in a range of domestic and industrial activities in regions with high solar insolation. However, the evaporation of water from these ponds is a significant problem that must be overcome for them to be deployed successfully. Thus, two ponds were constructed in the city of Nasiriya, Iraq. The two ponds were cylindrical with a diameter of 1.4 m and a total depth of 1.4 m. The water body in the two ponds was constructed with layer depths of 0.5, 0.75 and 0.1 m for the lower convective zone (LCZ), non-convective zone (NCZ) and the upper convective zone (UCZ) respectively. One of the two ponds was covered with a thin liquid paraffin layer (0.5 cm) to eliminate evaporation from the surface of the UCZ. The behavior of the standard SGSP and that of the covered pond with evaporation suppressed can be straightforwardly compared. The experimental units were run for six months from 1st of February to 31st of July 2019. It was shown in the first instance that by covering the pond with a thin layer of paraffin, that evaporation could be suppressed. The results showed that for the conventional SGSP, the temperature of the LCZ reached a maximum of ca. 76^◦C while in the covered pond the temperature of the LCZ was consistently lower than that in the uncovered pond by approximately 5–6^◦C. The results also indicated that the temperature of the UCZ in the covered pond was higher than that in the uncovered pond by about 10^◦C in the second half of the study period. However, it was noted that on rainy days the paraffin layer was swept away from the surface; and this could hinder the implementation of thin liquid cover in the large SGSP.