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13In this study, heat extraction from both the gradient and heat storage zones of a salinity-gradient 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 increases when the heat is removed from the lateral heat exchanger alone compared to either 1 using the bottom heat exchanger or using both heat exchangers simultaneously. pond was discovered as a natural phenomenon during the last century in Medve Lake in the 12Transylvania region in Romania. In this lake, temperatures up to 70°C were recorded at a depth 13 of 1.32 m at the end of the summer season (El-Sebaii et al., 2011; Bozkurt and Karakilcik, 2015). 14In practice, any pond with a black bottom is capable of collecting solar energy, but the collection 15 efficiency is poor because heated water at the bottom rises by convection to the top, where the 16 heat is rapidly dissipated to the environment. The convection currents can be minimized by the 17 presence of a strong density gradient from bottom to top (Weinberger, 1964; Bansal and Kaushik, 18 1981). This density gradient can be generated by using a high concentration of a salt such as 19NaCl at the bottom of the pond and low-salinity water at the top resulting in a configuration called 20 a salinity-gradient solar pond (SGSP). A typical SGSP consists of three distinct zones 21 (Zangrando, 1980; Tabor and Weinberger, 1981). The surface area formed by fresh water or low 22 salinity water is called the upper convective zone (UCZ) and it is a zone of constant temperature 23 close to the ambient air temperature and constant salinity between 2 and 3%. Below this UCZ, 24 there is an intermediate zone consisting of several layers with different densities. The brine 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 density gradually increases towards the bottom of the pond causing a concentration gradient. 1This gradient prevents the occurrence of convection currents and, as a result of solar energy 2 absorption, a gradient of temperature is also established. The gradient zone is known as the non-3 convective zone (NCZ) and it is the key to this technology. The lower zone has the highest 4 density (near saturation) and is known as the low convective zone (LCZ). This zone acts as a 5 thermal storage with temperature ranging between 50 and 90°C, depending on both the size of 6 the pond and the weather parameters. 7The heat accumulated in the SGSP has been conventionally extracted from the LCZ using two 8 methods. The first method is by withdrawing the hot brine from the upper region of LCZ by means 9 of a diffuser to prevent excessive velocities of motion within the pond and thereby minimizing the 10 e...

17In this study, an experimental investigation of the performance of a salinity gradient solar pond 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 Heat extraction and supply experiments are performed using both heat exchangers individually or but also increase the capacity of the solar pond to supply heat to an external application.

17A 500 m 2 industrial salinity-gradient solar pond (SGSP) was constructed in a mineral processing 18 plant (Solvay Minerales) in Granada (Spain). This renewable energy technology was designed to 19 supply a low-temperature heat (up to 60 ºC) to achieve the temperature requirements of the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64