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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, ΔT , between the
cold bottom and warm surface water resources meets or exceed the threshold 20°C
ΔT required for OTEC. In winter, the nearshore average ΔT of 17.76°C can
produce 59-75% design net power for a single 100 MW plant and 70-86% in spring
with ΔT averaging 18.25°C. Offshore along the southern transects, a high steady
ΔT 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.
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