Modelling the thermal potential and operation of salinity gradient solar ponds

Access to freshwater is crucial for socio-economic development. In Libya, the demand for freshwater is soaring, but the supply is limited. Freshwater is intrinsically linked to energy where the paramount consideration for its sustainability is the amount of energy required to guarantee sufficient supplies of freshwater through seawater-desalination. This emphasises two paramount needs that should be promptly sought as a national priority, first stringent water conservation, and second the employment of sustainable energy sources to power desalination. Salinity Gradient Solar Pond (SGSP) can be one of a mix of technologies leading to a future based on sustainable energy. This study models the potential and operation of SGSPs as a source of thermal energy in Libya. The study makes an original contribution to knowledge by explaining the essence (when, how,and where) of the SGSP operational instability. It also investigates the optimum zone thicknesses ratio of the three different salinity zones constituting the SGSP; Upper Convective Zone (UCZ), middle Non-Convective Zone (NCZ), and Lower Convective Zone (LCZ) while implementing the double-diffusive convection (DDC) phenomenon. One-dimensional and two-dimensional numerical studies are conducted. The results indicate that SGSP has the potential to provide hot saline-water at a temperature exceeding 70°C for multi-effect desalination thermal vapour compression units which require a minimum top brine temperature of 60 - 65°C. At a SGSP thermal output of 55 W m⁻², 46.8 m² of land is required for the production of 1 m³ per day of distillate. The two-dimensional study explains the nature of the operational instability where the occurrence and expansion of convective cells at the interfaces of the NCZ due to DDC leads to instability. This study also gathered evidence on the effect of buoyancy ratio. Salt concentration differences separating the UCZ and the LCZ should be sustained at 300 kg m⁻³ to maintain stability. The optimum zone thicknesses for an average SGSP of 2 m height are 0.4, 1.2, and 0.4 meters for the UCZ, the NCZ, and the LCZ, respectively.Access to freshwater is crucial for socio-economic development. In Libya, the demand for freshwater is soaring, but the supply is limited. Freshwater is intrinsically linked to energy where the paramount consideration for its sustainability is the amount of energy required to guarantee sufficient supplies of freshwater through seawater-desalination. This emphasises two paramount needs that should be promptly sought as a national priority, first stringent water conservation, and second the employment of sustainable energy sources to power desalination. Salinity Gradient Solar Pond (SGSP) can be one of a mix of technologies leading to a future based on sustainable energy. This study models the potential and operation of SGSPs as a source of thermal energy in Libya. The study makes an original contribution to knowledge by explaining the essence (when, how,and where) of the SGSP operational instability. It also investigates the optimum zone thicknesses ratio of the three different salinity zones constituting the SGSP; Upper Convective Zone (UCZ), middle Non-Convective Zone (NCZ), and Lower Convective Zone (LCZ) while implementing the double-diffusive convection (DDC) phenomenon. One-dimensional and two-dimensional numerical studies are conducted. The results indicate that SGSP has the potential to provide hot saline-water at a temperature exceeding 70°C for multi-effect desalination thermal vapour compression units which require a minimum top brine temperature of 60 - 65°C. At a SGSP thermal output of 55 W m⁻², 46.8 m² of land is required for the production of 1 m³ per day of distillate. The two-dimensional study explains the nature of the operational instability where the occurrence and expansion of convective cells at the interfaces of the NCZ due to DDC leads to instability. This study also gathered evidence on the effect of buoyancy ratio. Salt concentration differences separating the UCZ and the LCZ should be sustained at 300 kg m⁻³ to maintain stability. The optimum zone thicknesses for an average SGSP of 2 m height are 0.4, 1.2, and 0.4 meters for the UCZ, the NCZ, and the LCZ, respectively