Performance comparison of two new cogeneration systems for freshwater and power production based on organic Rankine and Kalina cycles driven by salinity-gradient solar pond

Solar energy can be stored and used via employment of SGSP (salinity-gradient solar pond) for low- and medium-temperature applications. Capturing thermal heat of a SGSP for cogeneration of electricity and freshwater for residential applications can lead to outstanding outcomes. To address this need, theoretical analysis of two cogeneration systems driven by a SGSP under the same conditions is carried out to produce freshwater and electricity by integrating an organic Rankine cycle (ORC) and a Kalina cycle (KC) with a reverse osmosis (RO) desalination unit. Also, a thermoelectric generator (TEG) with a heat exchanger is used as a potential device to improve performance of the systems in order to generate more power, using heat from upper convective zone. The energy and exergy balance equations are employed to different components of the systems for the Urmia lake in Iran, and the findings are credited by the available numerical and experimental data. The results of simulation demonstrated that the SGSP-ORC/RO system can provide freshwater and net electricity of 4 m3/h and 29.6 kW, respectively, when R600a is used in the ORC, while the SGSP-KC/RO system can produce freshwater and net output electricity of 3.3 m3/h and 15.5 kW, respectively. Under this condition, the cogeneration-based Gain-Output-Ratio (CGOR) and exergy efficiency for the SGSP-ORC/RO system are calculated 8.3 and 47.2%, respectively, whereas the CGOR and exergy efficiency for the SGSP-KC/RO system are calculated 6.9 and 26.0%, respectively. At last, a comprehensive parametric study is carried out to provide a technical enlightenment for designers of the systems. In comparison with the previous model, where a flat plate collector (FPC) with surface area of 21110 m2 was used to produce 145.8 m3h fresh water, it is found that the same fresh water amount can be attained with a solar pond with 35500 m2, hence obviously increasing pond area from this value will increase fresh water capacity of the proposed plant. •A SGSP for cogeneration of electricity and freshwater based on ORC and KC is used.•Performance of the proposed system is enhanced using TEG.•Feasibility of the proposed hybrid systems is investigated from first and second laws of thermodynamics viewpoint.•A comparative study between these two proposed hybrid systems is presented.