Abstract
Ocean thermal energy conversion (OTEC) is a power generation technology that extracts energy from the temperature difference between deep seawater and surface water in the ocean. Currently, a 100 kW class OTEC demonstration project is underway on Kume Island, Okinawa, and a plan to increase water intake and introduce a 1 MW class OTEC plant is under consideration. Year-round generation of electricity by an OTEC plant requires that it be installed in tropical and subtropical regions, where the surface water has a high temperature and low nutrient content. However, the water discharged from an OTEC plant will have the opposite characteristics of low water temperature and high nutrients, as well as a low pH. One of the most concerning environmental impacts of this discharged water is its influence on corals, which are important species in tropical and subtropical marine ecosystems. In this study, we developed an ecosystem model for a subtropical shallow-water region; the model combines a pelagic submodel, a chemical equilibrium submodel, and a benthic submodel, and successfully reproduces the observed variation in pH. The model was used to predict the environmental impact of water discharged from OTEC plant. The simulation results suggest that a 1 MW class OTEC plant would cause few environmental changes that would affect corals.