Effect of PCM melting temperature on solar ponds performance: Design and experimental investigation

Salt gradient solar pond (SGSP) is a technology which uses a renewable source such as solar energy to store thermal energy in a saline solution. Traditional SGSPs work in the sensible zone, increasing its temperature as the solar radiation is absorbed. SGSPs suffer from a low stability and energy efficiency, mainly caused by the high temperatures reached. At high temperatures, higher heat losses correspond. PCMs are characterized by high latent heat and a solid-liquid phase change at a nearly constant temperature. A pond integrated with PCMs can store the same amount of energy at a lower temperature, improving thermal efficiency and stability. In this paper, a pond integrated with PCM (RT35 HC) and a traditional one were designed, built and tested to evaluate the different performance. According to results, over ten days, the average temperature in the pond with the RT35 HC is about 4 °C lower (corresponding to the 5.7 %). Then a second experimental analysis was conducted comparing two different melting temperatures (RT35 HC and RT44 HC). Results show that a higher melting temperature enables to smooth the high peaks of temperature. While a lower melting temperature guarantees a higher and more stable temperature at night, due to the release of latent heat, making the application useful in case of constant temperature demand at the outlet fluid. Results are widely discussed in the paper.