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Renewable Energy from the OceanA Guide to OTEC$
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William H. Avery and Chih Wu

Print publication date: 1994

Print ISBN-13: 9780195071993

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195071993.001.0001

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Introduction and Overview

Introduction and Overview

(p.1) 1 Introduction and Overview
Renewable Energy from the Ocean

William H. Avery

Chih Wu

Oxford University Press

The sunlight that falls on the oceans is so strongly absorbed by the water that effectively all of its energy is captured within a shallow “mixed layer” at the surface, 35 to 100 m (100 to 300 ft) thick, where wind and wave actions cause the temperature and salinity to be nearly uniform. In the regions of the tropical oceans between approximately 15° north and 15° south latitude, the heat absorbed from the sun warms the water in the mixed layer to a value near 28°C (82°F) that is nearly constant day and night and from month to month. The annual average temperature of the mixed layer throughout the region varies from about 27°C to about 29°C (80 to 85°F). Beneath the mixed layer, the water becomes colder as depth increases until at 800 to 1000 m (2500 to 3300 ft), a temperature of 4.4°C (40°F) is reached. Below this depth, the temperature drops only a few degrees further to the ocean bottom at an average depth of 3650 m (12,000 ft). Thus, a huge reservoir of cold water exists below a depth of 3000 ft. This cold water is the accumulation of ice-cold water that has melted from the polar regions. Because of its higher density and minimal mixing with the warmer water above, the cold water flows along the ocean bottom from the poles toward the equator, displacing the lower-density water above. The result of the two physical processes is to create an oceanic structure with a large reservoir of warm water at the surface and a large reservoir of cold water at the bottom, with a temperature difference between them of 22 to 25 degrees Celsius (40 to 45 degrees Fahrenheit); this structure is found throughout the entire area of the tropical oceans where the depth exceeds 1000 m (3300 ft). The temperature difference is maintained throughout the year, with variations of a few degrees Fahrenheit due to the seasonal effects and weather, and day-to-night changes on the order of one degree. The ocean thermal energy conversion (OTEC) process uses this temperature difference to operate a heat engine, which produces electric power.

Keywords:   Argonne National Laboratory, biofouling, closed-cycle systems, efficiency, hydrogen, moored plantships, oceanographic survey data, position-control system

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