Study on the Fluid Selection and System Efficiency of Ocean Thermal Energy Conversion Technology

Study on the Fluid Selection and System Efficiency of Ocean Thermal Energy Conversion Technology

Climate change has been scientifically established as an urgent global challenge with significant impacts, drawing substantial international attention. In response, many countries have committed to achieving ''Net Zero Emissions by 2050'' and are actively implementing policies to mitigate its effects. Ocean thermal energy conversion (OTEC) technology has emerged as a promising renewable energy source, capable of generating electricity by exploiting the temperature difference between warm surface seawater and cold deep seawater. This study aims to analyze the performance of a dual-stage organic Rankine cycle system, recognized as one of the promising configurations for OTEC applications due to its enhanced efficiency in utilizing temperature differentials. A sensitivity analysis was conducted on 13 different working fluids to evaluate the impact of critical parameters on system performance, including seawater pipe diameter, pinch point temperature, and working fluid mass flow rate. The analysis employed MATLAB simulations based on seawater surface temperature data from the Heping area in Hualien, Taiwan, where Taiwan Cement Corporation proposed a 1 MW OTEC plant. The study identified optimal design parameters for each working fluid, revealing significant performance variations. Finally, this study includes an economic analysis to evaluate the levelized cost of energy and the feasibility of deploying OTEC technology on a commercial scale. Although the overall cost of the OTEC system employing R134a (tetrafluoromethane, a type of refrigerant) is slightly higher than that of ammonia, the findings indicate that R134a outperforms ammonia in thermal efficiency and economic viability, particularly highlighting significant advantages in the back-work ratio and net power output of the OTEC system. The findings also suggest that, with appropriate system design and optimization, OTEC technology can provide a stable and sustainable power supply, making it a viable option for regions with suitable thermal gradients, such as the South China Sea and tropical island nations.