Review of studies on enhancing thermal energy grade in the open ocean

Abstract

Ocean thermal energy conversion is one of the important ways to utilize low-grade ocean thermal energy. The main reasons for its low economic feasibility include high cost, small temperature difference, low energy efficiency, and high consumption of deep-sea cold energy extraction pumps. Some new means to improve the thermal energy grade may be beneficial to improve the economic feasibility of ocean thermal energy conversion, desalination, and other systems. The research progress and analysis results of ways to obtain low-grade thermal energy in the ocean surface by using solar energy, offshore platform waste heat, compressed air storage waste heat, and other methods show that (1) after using solar energy or waste heat to raise sea water temperature, shallow seawater can be used as the cold source, which can reduce most of the pump consumption and expensive riser cost of lifting cold seawater. This way improves the net power generation efficiency more significantly than improving the circulation mode and working medium and also significantly improves the economic feasibility. (2) Exhaust waste heat from offshore platform diesel power generation and compressed air energy storage power generation systems can be used to obtain a larger temperature difference between cold and hot seawater and further improve the efficiency of thermal power generation. (3) The low density of solar energy flow at the sea level leads to the high cost of offshore platforms. Incorporating ocean thermal energy conversion systems into floating photovoltaic power generation, seawater desalination and other systems can reduce the cost of offshore platforms.