OTEC Development in Hawaii
Almost all of the major U.S. OTEC experiments in recent years have taken
place in Hawaii. Natural Energy Laboratory
of Hawaii Authority (NELHA) has been recognized as the world's foremost
laboratory and test facility for OTEC and OTEC-related research. The facility
has been funded by the State of Hawaii with significant USDOE and private
sector participation.
There is no OTEC facility currently producing electricity at Keahole
Point. However, cold seawater is being used directly to air condition
(cool) the administration and laboratory buildings. The seawater provides
about 50 tons of air conditioning, offsetting the equivalent of 200 kW
of peak electrical demand. Using the cold seawater for air conditioning
saves NELHA nearly $4000 per month in electricity cost - and the system
requires much less maintenance than traditional compressor systems.
Mini-OTEC, 1979
In 1979, the first successful at-sea, closed-cycle OTEC operation in
the world was conducted aboard the Mini-OTEC, a converted Navy barge operating
in waters off Keahole Point. This plant operated for three months, from
August-October 1979, and generated approximately 50 kilowatts of gross
power with net power ranging from 10-17 kilowatts. Its turbine generator
produced a gross output of up to 55 kW. About 40 kW were required to pump
up 2,700 gallons/min of 42°F water from 2200-ft depth through a 24-in
diameter polyethylene pipe and an additional 2,700 gallons/min of 79°F
surface water, leaving a maximum net power output of 15 kW. This was a
joint effort by the State of Hawaii and a private industrial partner.
OTEC-1, 1980
In 1980, OTEC-1, a converted Navy tanker moored in waters off Kawaihae
on the Kona Coast, tested heat exchangers and other components of a closed-cycle
OTEC plant and investigated the environmental effects of an ocean-stationed
OTEC plant. It was not designed to generate electricity. This was a USDOE-funded
project.
Design and Continuing Research
Ocean Thermal Corporation, under a contract from the USDOE, in 1983 designed
a 40-megawatt OTEC pilot plant to be located on an artificial island at
Kahe Point off the coast of Oahu. The design plans were completed by the
end of 1984, but funds for construction of the plant were not forthcoming.
The relatively low cost of oil made OTEC noncompetitive with fossil-fuel
powered electric generating plants at that time.
A significant breakthrough which promises major reductions in the cost
of closed-cycle OTEC plants has been achieved through research on the
design of evaporators and condensers. The research has been conducted
at NELHA by ALCAN Aluminum of Canada and the Marconi Division of General
Electric Company of Great Britain.
A 210-kilowatt open-cycle OTEC
Experimental Apparatus was operated for onshore at NELHA's Keahole Point
facility intermittently between 1992 and 1998. providing valuable data
and pointing the way for future modifications and improvements in the
OC-OTEC process. The turbine-generator was designed for an output of 210
kW for 26 °C warm surface water and a deep water temperature 6 °C. It
produced a maximum gross output of 250 kW during late summer when the
surface water is warmest. Power requirements for pumping ashore the required
6,500 gpm of 43°F seawater through a 40-in pipe from 2700 ft depth
and 9600 gpm of 76-81°F surface seawater were about 200 kW. A small
fraction (10 percent) of the steam produced was diverted to a surface
condenser for the production of desalinated water. The highest production
rates achieved were 255 kW (gross) with a corresponding net power of 103
kW and production of approximately 6 gallons per minute
of desalinated water. These are world records for OTEC. It must be noted
that the net power was not optimized because pumping losses were relatively
high due to the use of a seawater system that was already available. It
is expected that for a commercial size plant the ratio of net to gross
power will be approximately 0.7.
A preliminary design was prepared for a 1.4 MW (gross) OTEC plant to
utilize the seawater available through NELHA's new 55-in diameter surface
and deep pipelines, which were installed primarily to provide seawater
for developing aquaculture businesses. The total pumping load for full
flow (27,000 gal/min deep seawater from 3000-ft depth at 39°F, and
40,500 gal/min surface water at 76-81°F) will be about 1 MW, so there
is the potential to produce up to 400 kW net output. This project has
not materialized because the State (NELHA) and the OTEC proposer have
been unable to find a financially viable solution to accommodate the gradual
scale-up required by the seawater needs of the other users.
Research in both closed-cycle and open-cycle OTEC and OTEC-related aquaculture
continues at NELHA. International exchange of technical information between
researchers in both areas is on-going.
Related Aquaculture Activities, Kailua-Kona,
Hawaii
A new seawater system has been installed to serve the acquaculture activities
of the Hawaii Ocean Sciene and Technology (HOST) Park. 55-inch diameter
pipelines bring ashore 4°C deep water from 3000 ft depth and 27.5°-28.5°C
surface water from 80 ft depth.
The pipelines will primarily serve aquaculture tenants in the HOST Park,
but companies are discussing proposals to construct an OTEC plant that
will provide electricity to power the pumps, reducing the pumping cost
for all tenants.
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