Wednesday, August 4, 2010
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Average ocean temperature differences (at water depths of between 20 meters and 1000 meters depths) around the main Hawaiian Islands for the period July 1, 2007, through June 30, 2009, (the color palette is from 18°C to 24°C); the relatively more favorable area in the lee of the islands is clearly visible. Credit: Data from HYCOM (an academia-industry consortium, see: http://www.hycom.org/ and NCODA, public data from the U.S. Navy, see: https://www.fnmoc.navy.mil/public/. Image provided by Gerard Nihous.
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Researchers
at the University of Hawaii at Manoa say that the Leeward side of
Hawaiian Islands may be ideal for future ocean-based renewable energy
plants that would use seawater from the oceans' depths to drive massive
heat engines and produce steady amounts of renewable energy.
The
technology, referred to as ocean thermal energy conversion (OTEC), is
described in the Journal of Renewable and Sustainable Energy, which is
published by the American Institute of Physics (AIP).
It
involves placing a heat engine between warm water collected at the
ocean's surface and cold water pumped from the deep ocean. Like a ball
rolling downhill, heat flows from the warm reservoir to the cool one.
The greater the temperature difference, the stronger the flow of heat
that can be used to do useful work such as spinning a turbine and
generating electricity.
The
history of OTEC dates back more than a half century. However, the
technology has never taken off -- largely because of the relatively low
cost of oil and other fossil fuels. But if there are any places on Earth
where large OTEC facilities would be most cost competitive, it is where
the ocean temperature differentials are the greatest.
Analyzing
data from the National Oceanic and Atmospheric Administration's
National Oceanographic Data Center, the University of Hawaii's Gérard
Nihous says that the warm-cold temperature differential is about one
degree Celsius greater on the leeward (western) side of the Hawaiian
Islands than that on the windward (eastern) side.
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An example of early OTEC field work in Hawaii: aerial view of the land-based experimental open-cycle OTEC plant that operated between 1993 and 1998 on the Big Island. The facility still holds the world record for OTEC power production, with turbo-generator output exceeding 250 kW and more than 100 kW of net power exported to the grid. Credit: Luis Vega
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This
small difference translates to 15 percent more power for an OTEC plant,
says Nihous, whose theoretical work focuses on driving down cost and
increasing efficiency of future facilities, the biggest hurdles to
bringing the technology to the mainstream.
"Testing
that was done in the 1980s clearly demonstrates the feasibility of this
technology," he says. "Now it's just a matter of paying for it."
More information in the project, see: http://hinmrec.hnei.hawaii.edu/ongoing-projects/otec-thermal-resource/
The
article, "Mapping available Ocean Thermal Energy Conversion resources
around the main Hawaiian Islands with state-of-the-art tools" by Gérard
C. Nihous will appear in the Journal of Renewable and Sustainable
Energy. See: http://jrse.aip.org/jrsebh/v2/i4/p043104_s1
Nihous'
research is supported by the University of Hawaii's National Marine
Renewable Energy Center, which is funded by the U.S. Department of
Energy. See: http://hinmrec.hnei.hawaii.edu/
SOURCE
