Ocean Thermal Energy Capacity Estimation and Resource Assessment of Southeast Florida

Abstract

Abstract Florida Atlantic University, in collaboration with Lockheed Martin, has performed an ocean thermal resource assessment off Florida's Southeast coast. Thermal properties in the Straits of Florida are characterized using a series of at-sea measurements and site specific single plant energy production estimates have been calculated using a parametric model of a 100 MW Ocean Thermal Energy Conversion system. The Straits of Florida off of Florida's Southeast coast contain significant volumes of cold and warm water that are advected northward by the Florida Current. This resource is located within 8 km of shore in water as shallow as 250 m with a larger, more consistent resource further from shore. Direct measurements of the temperature profile and other water properties were taken from nearshore Southeast Florida to the Exclusive Economic Zone boundary along four evenly spaced transects perpendicular to Florida's Southeast coast, spanning 160 km. Data are used to characterize the local bathymmetry, water properties, thermal structure, the seasonal variations of the ocean thermal resource, and identify sites with potential for ocean thermal energy deveopment. Along the southern transects in summer, the nearshore temperature difference, ?T, between the cold bottom and warm surface water resources meets or exceed the threshold 20°C ?T required for OTEC. In winter, the nearshore average ?T of 17.76°C can produce 59-75% design net power for a single 100 MW plant and 70-86% in spring with ?T averaging 18.25°C. Offshore along the southern transects, a high steady ?T from 18.5-24°C creates an annual average net power production potential of 120-125MW, exceeding the proposed design production. Along the northern transects, the nearshore resource does not exist, but a consistent OTEC resource is present offshore, providing 70- 80% design net power in winter and 100-158% in spring and summer. Introduction According to the U.S. Department of Energy, fossil fuels, including coal, oil and natural gas, provide 84% of all energy produced in the United States - nuclear and renewable energy account for 9% and 7% respectively (" Renewable energy consumption,?? 2009). Volatile oil prices and environmental, ecological, and security concerns have lead to increased interest in clean renewable energy resources. An attractive energy source that has yet to be thoroughly explored commercially is ocean thermal energy. Ocean thermal energy is a form of energy that is derived from the temperature of the ocean's water and it can be used to provide electricity, air conditioning, and freshwater. The source of this energy is the heating of the ocean's surface by the incident solar radiation and the cooling that occurs in the Polar Regions. The natural circulation patterns of the oceans act as energy conveyers that deliver water masses throughout the globe. Ocean thermal potential is huge, yet remains relatively unknown. For example, the 60 million square km of tropical ocean waters absorb the energy equivalent in heat content to 245 billion barrels of oil each day. While extracting this much energy is unrealistic, impractical, unnecessary and certainly unsustainable, harnessing a fraction of a percent of this ocean thermal energy could supply a meaningful portion of the total daily U.S. electrical consumption (" Ocean thermal,?? 1989). Electricity can be produced using the heat stored in the warm surface water and colder, deeper water to power thermodynamically driven generators (Vega, 2002/2003) in a process known as Ocean Thermal Energy Conversion (OTEC). OTEC is a very attractive method to provide clean renewable energy in many areas of the world, with the present focus directed on small islands in tropical waters with a high cost of electricity. However, South Florida, with its growing energy demand, rising electricity costs, high coastal population densities, direct connection to the U.S. national grid and close proximity to cold and warm water resources is also considered a prime candidate for ocean thermal applications.