OTEC Power Efficiency Challenges

Abstract

Abstract The maximum possible Carnot thermal efficiency of an Ocean Thermal Energy Conversion (OTEC) power system is about 7% as it exploits the water temperature gradient between the surface and the deep ocean, which is only slightly over 20 degree C in tropical waters. The overall efficiency of a multi-megawatt-sized OTEC electrical power plant, all inclusive from seawater to net electric power, is typically around 2%. Only about half of the water temperature gradient can be directly harnessed across the power cycle, as the rest is needed for heat transfer and mass flow to maintain economical heat exchanger and seawater pump sizing. About a third of the gross power generated is consumed pumping seawater, powering auxiliary systems, and in power transmission losses. This paper reviews efficiency as it relates to the OTEC power cycle. OTEC has enormous potential as a source of clean, renewable, and base-load electricity for many nations, territories and states near tropical waters. As OTEC technology matures, large floating OTEC plants are expected to produce energy carriers or synthetic fuels that can be shipped to energy consumers. This paper will provide a current review of the various components used by one OTEC power cycle, their respective efficiencies and their contribution to the overall OTEC power plant economics. A thorough understanding of the efficiency losses, power burden, and potential areas for optimization is critical for OTEC to become an economically viable resource. This paper provides recommendations for the design of the OTEC plant main components and gives guidelines to optimize efficiency such that high quality power can be sold to the utility at competitive rates. Finally, the results of a parametric study of OTEC size in terms of Megawatts produced shows the efficiency gains that can be achieved with large scale OTEC power generation plants. I. Introduction Global energy demand is increasing rapidly. Growing populations and higher standards of living worldwide are pushing the limits of existing energy resources. At the same time hydrocarbon reserves are becoming harder to find. There is growing global concern for energy security and environmental sustainability. Global development and commercialization of renewable technologies is required before existing resources become scarce. For instance: wind energy has been used through the centuries but was surpassed during the Industrial Revolution by coal and oil. However, over the past decade, wind power has seen exponential growth as an energy resource (2009 US DOE). Solar and wind energy have the economic advantage of free " fuel?? but come with the intermittent and variable nature of that " fuel?? source. Ocean thermal energy enjoys the benefit of the large thermal storage of ocean waters and can therefore provide a base-load source of electricity to coastal areas in tropical waters and energy carriers to energy consumers. Figure 1 is a map showing the vast worldwide OTEC resource.