Optimal design of hybrid ocean thermal energy and solar pond system

• A hybrid ocean thermal energy and solar pond system is proposed to improve OTEC . • Multi-variable optimal design under time-varying weather condition is conducted. • LCOE LC of suggested hybrid system is reduced by 33.5% compared to OTEC using R717. • Fourth-generation refrigerant R600a-R1233zd(E) is a viable alternative to R717. • LCOE LC of optimized hybrid system using R600a-R1233zd(E) is 0.417USD/kWh. Ocean thermal energy is a promising renewable energy to supply sustainable electricity for island development, but the thermo-economic performance of ocean thermal energy conversion (OTEC) is not satisfactory due to its small usable temperature difference. This paper suggests a hybrid ocean thermal energy and solar pond system to expand the usable temperature difference of the OTEC. A thermo-economic model is developed for the hybrid system, and a multi-variable optimization method is proposed to explore its optimal design under the time-varying weather conditions, aiming to minimize the levelized cost of electricity considering the off-design conditions (LCOE LC ). The results indicate that introducing a solar pond into an OTEC system is an effective way to improve the thermo-economic performance of developing ocean thermal energy. The LCOE LC of the hybrid system using R717 is reduced by 33.5% compared to a traditional OTEC system using R717. Moreover, as a typical representative of the 4th generation of environmentally friendly refrigerants, the binary mixture R600a-R1233zd(E) with temperature-glide characteristics is an ideal alternative to R717. Due to its small irreversible losses during evaporation and condensation, the optimized hybrid system using R600a-R1233zd(E) exhibits a minimal LCOE LC of 0.417USD/kWh, representing a 34.1% reduction compared to the hybrid system using R717.