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Abstract
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.
Highlights
There is a broad consensus around the world that the solution to many energy supply and environmental problems is through the use of alternative energy sources or renewable energy
The body of water in a salinity gradient solar pond (SGSP) consists of three distinct layers: the lower convective zone (LCZ), the non-convective zone (NCZ) and the upper convective zone (UCZ)
It was observed that dust mostly accumulated on the surface of the paraffin layer and had an influence on the incident solar radiation which penetrates to the LCZ; this contributed to its temperature being lower than the uncovered pond by approximately 5–6◦C
Summary
Population growth and modern lifestyles that are increasingly dependent on electricity, the rising demand for energy and the ability to deliver it cleanly has become more problematic. Sayer et al [32] investigated theoretically the improvement of SGSP by suppressing surface evaporation with an air layer Their results for a year-long period illustrated that adding the air cover improved the LCZ temperature with a total average increase of approximately 9% over the conventional pond (uncovered). Seeking to extend the heat extraction time from the lower zone of a pond, Beika et al [33] proposed using paraffin wax as a phase change material (PCM) in the lower zone of a solar pond Their analysis involved the use of a one-dimensional numerical model to investigate the transient behaviour of the temperature distribution in the pond. Das [37] investigated the conventional assumptions that have been used to simulate the effect of ground heat extraction using different overall heat transfer coefficient values with closed form solutions They obtained results for how the temperature distribution of the three zones deviated from the ideal temperature distribution. Evaporated water from the surface needs to be substituted to replenish the UCZ and this will increase operating costs
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