Exergo-economic assessment of OTEC power generation

Ocean Thermal Energy Conversion is an important renewable energy technology aimed at harvesting the large energy resources connected to the temperature gradient between shallow and deep ocean waters, mainly in the tropical region. After the first small-size demonstrators, the current technology is focused on the use of Organic Rankine Cycles, which are suitable for operating with very low temperatures of the resource. With respect to other applications of binary cycles, a large fraction of the output power is consumed for harvesting the resource - that is, in the case of OTEC, for pumping the cold and hot water resource. An exergy analysis of the process (including thermodynamic model of the power cycle as well as heat transfer and friction modelling of the primary resource circuit) was developed and applied to determine optimal conditions (for output power and for exergy efficiency). A parametric analysis examining the main design constraints (temperature range of the condenser and mass flow ratio of hot and cold resource flows) is performed. The cost of power equipment is evaluated applying equipment cost correlations, and an exergo-economic analysis is performed. The results allow to calculate the production cost of electricity and its progressive build-up across the conversion process. A sensitivity analysis with respect to the main design variables is performed.