Determination of optimum insulation thicknesses for salinity gradient solar pond’s bottom wall under different climate conditions

The salinity gradient solar pond is one of the most efficient tools that can be used to collect, convert and store the solar energy. The performance of solar pond specially depends on heat losses from it. The performance of the solar pond could be improved by using the thermal insulation on the bottom and sides of the solar pond. Determination of insulation thickness is very important; it is commonly estimated based on the climate conditions, insulation materials and economic parameters. Therefore, in this study, the optimum insulation thickness, cost and energy savings were calculated for a salinity gradient solar pond under different climate conditions. An economic analysis was applied to obtain the optimum value of the insulation thickness when the polyurethane was used as the insulation material. For this purpose, the temperature of the lower layer of the solar pond was calculated using the one-dimensional unsteady heat transfer model inside the pond. The model and the literature experimental lower layer temperatures showed a good agreement, with the average deviation of 5%. They also had the same trend in all months of the year. The results revealed that the optimum insulation thickness strongly depended on the solar irradiance and the ambient temperature. This study also found that by introducing the optimum insulation thickness of 62–122 mm, according to the climate conditions, in the solar pond’s bottom wall, the energy saving could be enhanced by 36.7–55.2% as compared with the solar pond without insulation.