Standardization Proposal for Exergy Analysis of Ocean Thermal Energy Conversion Power Cycles

There is a need to reduce carbon dioxide emissions to mitigate the effects of climate change. One of the solutions lies in the ocean thermal energy conversion (OTEC) systems. When reviewing the literature, it is evident that the exergy analysis of these systems does not follow any established standard. Therefore, a standard is proposed in this work: to consider the reference environment temperature as the temperature of the warm surface water and associate the cold deep water temperature with the exergy input of the cycles. Firstly, reversible power cycles are studied. Subsequently, an organic Rankine cycle (ORC) is analyzed. Approaches found in the literature are also applied to analyze the ORC. It is shown that, for any reversible power cycle, when the hot reservoir temperature equals the reference environment temperature, the work produced by the cycle equals the exergy accompanying the heat transfer associated with the cold reservoir temperature. For an ORC, taking the reference environment temperature as the warm surface water temperature and considering the exergy input as the exergy change of the deep cold water in the condenser generates robust and coherent results. The proposed standard can contribute to the systematic advancement of scientific knowledge on OTEC systems.