Performance analysis of a closed-cycle ocean thermal energy conversion system with solar preheating and superheating

The research presented in this thesis provides thermodynamic insights on the potential advantages and challenges of adding a solar thermal collection component into ocean thermal energy conversion (OTEC) power plants. In that regard, the article reports the off-design performance analysis of a closed-cycle OTEC system when a solar thermal collector is integrated as an add-on preheater or superheater into the system. The present research aims to examine the system-level effects of integrating solar thermal collection with an existing OTEC power plant in terms of power output and efficiency. To this end, the study starts with the design-point analysis of a closed-cycle OTEC system with a 100 kW gross power production capacity. The numerically designed OTEC system serves as an illustrative base which lays the ground for thermodynamic analysis of off-design operation when solar thermal collection is integrated. Two methods that make use of solar energy are considered in this research. Firstly, an add-on solar thermal collector is installed in the system in order to preheat the surface seawater before it enters the evaporator. The second way considered is directly superheating the working fluid between the evaporator and the turbine with the add-on solar thermal collector. Numerical analysis is conducted to predict the change of performance (i.e., net power and efficiency) within the OTEC system when solar collection is integrated as a preheater/superheater. Simulated results are presented to make comparison of the improvement of system performance and required collector effective area between the two methods. In the conclusion, possible ways to further improve the solar collector efficiency; hence the overall thermal efficiency of the combined system are suggested. Obtained results reveal that both preheating and superheating cases increase the net power generation by 20-25% from the design-point. However, the preheating case demands immense heat load on the solar collector due to the huge thermal mass of the seawater, being less efficient thermodynamically. Adverse environmental impacts due to the increase of seawater temperature are also of concern. The superheating case increases the thermal efficiency of the system from 1.9 % to ~3%, about 60% improvement, suggesting that it should be a better and more effective approach in improving a closed-cycle OTEC system