Effects of oceanic flow patterns on the thermal efficiency of Ocean Thermal Energy Conversion (OTEC)

Abstract

This analysis examines the flow patterns produced by the intake of both warm and cold water into a OTEC power plant. It also examines the mixing and possible recirculation of waters discharged from the OTEC plant back to the ocean. Since no OTEC power plant now exists in large or small size, it is important to forecast and identify possible problem areas for future work. A specific case study is made of a plant nominally designed to produce 200 MW of power. A parameterized description is developed to aid in the mathematical analysis of the principal features of the oceanic flow patterns for the OTEC power plant. From this analysis, it is shown, for the 200 MW plant, that recirculation of ocean water, as large as 40 percent of the evaporator discharge flow reduces power output by less than 10 percent. Some pattern of evaporator recirculation is likely to occur. It is an important result of this study to show that such recirculation is neither critical to plant operation nor an expected cause of instability, that is, the plant does not shut itself off by evaporator recirculation. Condenser (cold) water recirculation into the evaporator (warm) water intake is much moremore » critical than a recirculation between evaporator discharge and intake. Fortunately, discharge flow patterns appear to provide a simple basis to assure that this kind of recirculation can be wholly avoided. A simple, but useful, analysis of the heat budget for the Caribbean Sea is examined in order to address some questions on the impact of large numbers of OTEC facilities in the tropical ocean. The analysis presents a relationship between net power withdrawal and reduction in ocean mixed layer (surface) temperature for several possible ocean flow conditions.« less