Abstract
This study aims at offering a techno-economic evaluation of closed OTEC cycles for on-shore installations. A flexible Matlab® suite has been developed to identify plant design parameters (temperature difference of cold and warm seawater, pinch-point temperature difference of evaporator and condenser etc.) that guarantee the maximum value of γ (ratio between electricity output and heat exchangers area). The optimization model is able to handle different working fluids through the addition of specific correlations that consider fluid influence on heat transfer coefficients and turbine performance. Each plant component is technically analyzed and, in particular, plate heat exchangers were considered for evaporator and condenser and sized accurately with Aspen EDR®, while expander was analyzed with the in-house code Axtur. For warm seawater temperature of 28 °C and cold seawater temperature of 4 °C (8500 kg/s taken from 1000 m depth), ammonia cycle is the best solution characterized by efficiency equal to 2.2% and net power output equal to 2.35 MWe.
The obtained LCOE (269 €/MWhe) confirms how OTEC technology is not ready to compete in energy market. Nevertheless, remote zones (i.e. small islands archipelagos), which are often characterized by high electricity price, represent interesting scenarios where OTEC technology could be a promising alternative to conventional power production technologies.