A comparative study of the performance of solar ponds under Middle Eastern and Mediterranean conditions with batch and continuous heat extraction

This study presents a novel heat extraction method, which can be operated in batch or continuous, modes for salinity gradient solar ponds. A comparison between the performance of two solar ponds of the same size (10,000 m2) in Adana (Turkey) and Ahvaz (Iran) is also presented. The heat extraction method entails brine removal from the non-convective zone (NCZ) as well as the heat storage zone (HSZ). The presented model incorporates the heat losses from the bottom and surface of the pond as well as the cooling effect imposed as a consequence of the replacement of extracted brine from each layer, and the supply of freshwater to the surface of the pond to maintain its inventory. The model can be employed to predict the performance of solar ponds of various dimensions for any given location. It was established that the pond modelled for Ahvaz would perform 30% better than the pond in Adana in both batch and continuous heat extraction modes, predominantly due to the higher quantities of solar energy reaching the surface of the pond and the higher air temperatures throughout the year at this location. The quantities of heat provided in the first year of operation from the ponds in Adana and Ahvaz in batch mode extraction are 2.8 x 106 MJ and 4.0 x 106 MJ, respectively. These values are approximately three times higher than those from the continuous mode of heat extraction due to the larger volume of withdrawal in the batch mode. Using the proposed heat extraction method in batch mode, 85% of the total heat is removed from the HSZ while this is just over 50% for the continuous mode indicating the better energy storage performance of the batch mode. Both heat extraction modes offer an efficient mechanism of stabilising a temperature gradient throughout the pond with the aim of insulating the HSZ for heat storage. This is carried out by designating brine removal thresholds of 70 °C, 80 °C and 90 °C within the NCZ and 95 °C in the HSZ. It is also demonstrated that the requirement for the supply of freshwater to the surface of solar ponds is significantly dependant on the wind velocity at each location and is unaffected by the mode of heat extraction

Behaviour of a salinity gradient solar pond during two years and the impact of zonal thickness variation on its performance

The interest in solar energy has increased substantially as a consequence of greenhouse gas emissions that result from the combustion of fossil fuels in power generation processes. Solar energy is likely to be the energy of the future and solar ponds, in particular, salinity gradient solar ponds (SGSP), facilitate simple and cost-effective thermal energy collection and storage. In this study; the influence of varying the thicknesses of the zones present in a salinity gradient solar pond on the temperatures of the upper convective zone (UCZ) and the lower convective zone (LCZ) is investigated. The study finds that thickness variation of the zones within the pond has a considerable impact on the temperature of the LCZ while it has a small effect on the temperature of the UCZ. The optimal thicknesses of the UCZ and the non-convective zone (NCZ) have been found to be 0.2 and 2 m respectively. The results also show that the type of application plays a substantial role in determining the depth of the LCZ, and that temperature of this zone varies with the rate of heat extraction. A period of no heat extraction is required to allow the pond to warm up and the length of this period depends on the depth of the LCZ, the type of application coupled with the pond, and the rate of heat extraction. It was found that the SGSP could be deeper with less surface area, and still suitable for applications that require low-grade heat. These findings could form the basis of future studies regarding the performance and financial viability of the overall depth of SGSPs