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Research Papers: Alternative Energy Sources

An Assessment of Global Ocean Thermal Energy Conversion Resources With a High-Resolution Ocean General Circulation Model

[+] Author and Article Information
Gérard C. Nihous

e-mail: nihous@hawaii.edu
Department of Ocean and Resources Engineering,
University of Hawaii,
Honolulu, HI 96822

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1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received January 1, 2013; final manuscript received February 12, 2013; published online May 31, 2013. Assoc. Editor: Kau-Fui Wong.

J. Energy Resour. Technol 135(4), 041202 (May 31, 2013) (9 pages) Paper No: JERT-13-1002; doi: 10.1115/1.4023868 History: Received January 01, 2013; Revised February 12, 2013

Global rates of ocean thermal energy conversion (OTEC) are assessed with a high-resolution (1 deg × 1 deg) ocean general circulation model (OGCM). In numerically intensive simulations, the OTEC process is represented by a pair of sinks and a source of specified strengths placed at selected water depths across the oceanic region favorable for OTEC. Results broadly confirm earlier estimates obtained with a coarse (4 deg × 4 deg) OGCM, but with the greater resolution and more elaborate description of key physical oceanic mechanisms in the present case, the massive deployment of OTEC systems appears to affect the global environment to a relatively greater extent. The maximum global OTEC power production drops to 14 TW, or about half of previously estimated levels, but it would be achieved with only one-third as many OTEC systems. Environmental effects at maximum OTEC power production are generally similar in both sets of simulations. The oceanic surface layer would cool down in tropical OTEC regions with a compensating warming trend elsewhere. Some heat would penetrate the ocean interior until the environment reaches a new steady state. A significant boost of the oceanic thermohaline circulation (THC) would occur. Although all simulations with given OTEC flow singularities were run for 1000 years to ensure stabilization of the system, convergence to a new equilibrium was generally achieved much faster, i.e., roughly within a century. With more limited OTEC scenarios, a global OTEC power production of the order of 7 TW could still be achieved without much effect on ocean temperatures.

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Figures

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Fig. 1

26°N zonal integrals of the North Atlantic velocity fields multiplied by the appropriate layer thicknesses (Sv) as a function of depth (m): MITgcm calculations are yearly averages after 1000-year spin-up (this work); other results are 1992–2004 time means under data constraints [17]

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Fig. 2

Long-term (1000 year) yearly averaged global OTEC power as a function of OTEC flow intensity wcw (m yr−1)

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Fig. 3

Yearly averaged global OTEC power as a function of time for different OTEC flow intensities wcw (m yr−1)

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Fig. 4

Variation of yearly averaged OTEC power density (kW m−2) when wcw = 20 m yr−1. (a) Initial field (no feedback from OTEC plants), (b) 5 year feedback, (c) 25-year feedback, (d) 50 year feedback, (e) 100 year feedback, and (f) 200 year (nearly asymptotic) feedback.

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Fig. 5

Long-term (1000 year) yearly averaged temperature change ( °C) in the surface layers (55 m) when wcw = 20 m yr−1 (the OTEC region is within the black line)

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Fig. 6

Long-term (1000 year) yearly averaged temperature change ( °C) in deep-seawater-intake layer (centered at 1160 m depth) when wcw = 20 m yr−1 (the OTEC region is within the black line)

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Fig. 7

Long-term (1000 year) yearly averaged strength of the Atlantic thermohaline circulation (Sv) as a function of OTEC flow intensity wcw (m yr−1)

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Fig. 8

Long-term (1000 year) yearly averaged temperature change (°C) in the surface layers (50 or 55 m) at 58°N, 46°W as a function of OTEC flow intensity wcw (m yr−1)

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