Renewable Energy Sources for Caribbean
Territories and SIDS: OTEC
M. L. Anderson, 2009
Ocean Thermal Energy Conversion
Ocean Thermal Energy Conversion

Ocean thermal energy conversion (OTEC) is a
method for generating electricity which uses the
temperature difference that exists between deep
and shallow waters
OTEC: What is it?
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Thermal energy- form of energy that manifests itself as
an increase of temp.
Method for generating electricity.
Runs a heat engine- a physical device that converts
thermal energy to mechanical output
Uses temp. difference that exists b/w deep & shallow
waters.
Temperature difference between warm surface water
and cold deep water must be >20°C (36°F) for OTEC
system to produce significant power.
Background Information
 60 million km2. (23 million miles2) of tropical seas absorb a
tremendous amount of solar radiation.
 Heat content equal to about 250 billion barrels of oil.
 If less than 1/10th of 1% of this stored solar energy.
converted to electric power, it would supply more than 20
times the total amount of electricity consumed in the U.S.
on any given day.
Ocean Thermal Energy
Conversion (OTEC)

Ocean Thermal Energy
Conversion produces
electricity from the natural
thermal gradient of the
ocean, using the heat
stored in warm surface
water to create steam to
drive a turbine, while
pumping cold, deep water
to the surface to recondense the steam.
Ocean
Thermal
Energy
Conversion

Ocean Thermal Energy Conversion is only viable in the
tropical seas, in areas where the thermal gradient between
the surface and a depth of 1000m is at least 22°C.
Ocean Thermal
Energy
Conversion
(OTEC)
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Generates power with temperature differential between
warm surface water and cooler, deep water
Requires temp differential of 36 F
50 kW mini-OTEC plant in Hawaii operated in the ’80s
OTEC limited applications
– Very costly
– Limited suitable sites
– can’t justify for electricity – must also desalinize, sustain
aquaculture, etc…
The Technologies:
Ocean Thermal
Energy Conversion
(OTEC)
Ocean’s natural thermal gradient (warm surface waters,
cold deep waters) drives power-producing cycle
 OTEC converts solar radiation to electric power

– Tropical seas cover 60 million km2 -- world’s largest

solar collector
– Solar radiation absorbed on average day equal in heat
content to ~250 billion barrels of oil
Three types of OTEC systems: open, closed, and hybrid
Closed Cycle OTEC
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In closed-cycle OTEC, warm seawater
heats a working fluid, such as
ammonia, with a low boiling point,
such as ammonia, which flows through
a heat exchanger (evaporator).
The ammonia vapor expands at
moderate pressures turning a turbine,
which drives a generator which
produces energy.
OTEC: Closed Cycle
The vapor is then condensed in another heat
exchanger (condenser) by the cold, deep-ocean water
running through a cold water pipe.
 The working fluid (ammonia) is then cycled back
through the system, being continuously recycled.

Open Cycle OTEC
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In an open-cycle OTEC plant, warm seawater from the
surface is the working fluid that is pumped into a
vacuum chamber where it is flash- evaporated to
produce steam at an absolute pressure of about 2.4
kilopascals (kPa).
The resulting steam expands through a low-pressure
turbine that is hooked up to a generator to produce
electricity.
The steam that exits the turbine is condensed by cold,
deep-ocean water, which is returned to the environment.
If a surface condenser is used, the condensed steam
remains separated from the cold ocean water and can be
collected as a ready source of desalinated water for
commercial, domestic or agricultural use.
OTEC Open Cycle System

In an open-cycle plant, the warm water, after being
vaporized, can be re-condensed and separated
from the cold seawater, leaving behind the salt and
providing a source of desalinated water fresh
enough for municipal or agricultural use.
OTEC Hybrid Cycle System
Hybrid plants, combining benefits of the two systems, would
use closed-cycle generation combined with a second-stage
flash evaporator to desalinate water.
History
Jacques Arsene d’Arsonval
1881- Jacques Arsene d’Arsonval, French physicist,
proposed tapping the thermal energy of the ocean.
 1930- Georges Claude, d’Arsonval’s student, built the 1st
OTEC plant in Cuba.
 1935- Claude constructed another plant aboard a 10,000
ton cargo vessel off the coast of Brazil.
 Weather & waves destroyed both plants before they could
become net power generators.

History Cont.
Ivory Coast
 1956- French scientists designed another OTEC plant for
Abidjan, Ivory Coast, West Africa.
 The plant was never completed due to reduced energy costs.
Large amounts of cheap oil became available in the 1950’s.
 1962- J. Hilbert Anderson & James H. Anderson, Jr. started
designing a cycle that focused on developing new, more efficient
component design.
 1967- patented new "closed cycle" design.
History, Con’t.
 1970- Tokyo Electric Power Company successfully built &
deployed a 100 kW closed-cycle OTEC plant on the island of
Nauru.
Japan
 1981- Became operational
 Produced about 120 kW of electricity .
 90 kW was used to power the plant & the remaining electricity
used to power a school & several other places on Nauru.
 Set a world record for power output from an OTEC system
where the power was sent to a real power grid.
OTEC Development
The Tokyo Power Company built a 100 kW shore-based closed
cycle pilot power plant on the island of Nauru, in 1981. The
pilot plant achieved a net output of 31.5 kWe during
continuous operation, proving the principle of OTEC is a viable
energy alternative. The plant is now decommissioned.
Postage stamps commemorating the OTEC pilot project located on Nauru.
India and OTEC

The government of
India has taken an
active interest in
OTEC technology.
 India has built and
plans to test a 1 MW
closed-cycle, floating
OTEC plant.
Land Based Plants
…Have both advantages and disadvantages over shelf based
and floating plants.
 Unlike those plants that are on the ocean shelf or floating in
the open ocean, land based plants do not require long cables
or anchors that are very expensive.
 They require less maintenance and can be installed in areas
that are sheltered from storms which could possibly destroy
the plant.
 In addition, land based plants can support mariculture using
desalinated water.
 However, land based plants are subject to the extremes of the
surf zone, heavy seas and storms. This causes stress on the
water supply and discharge pipes.
 The problem could be helped if the pipes were buried in
trenches, or if the plant were moved into water 10-30 meters
deep, but this presents erosion problems as well.

Shelf-Based Plants

OTEC plants can be placed on the continental shelf,
down to depths of no more than 100 meters.
 The same kind of construction that is used to build
offshore oil rigs would be used to build shelf-based
plants.
 These plants would have problems with product
delivery and the stressors of the open ocean.
 Working these plants in water 100 meters deep also
presents problems and these plants are more
expensive than the land-based plants.
Floating Plants

They are not tied to a land base and therefore require
long and expensive cables that would get tangled and
need repair.
 If the base was not kept stable, the cold water pipe might
break, especially during high seas and storms.
 However, this problem could be solved by using flexible
polyethylene to attach the pipe to the bottom of the plant
along with joints and collars.
 Instead of using a warm water pipe, the floating OTEC
plant could simply draw in the warm water from the
surface. But, storms and high seas can interrupt the
water flow and cause major damage to the plant.
US OTEC Development
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The US has taken the
lead in OTEC/DOWA
development, primarily
through work carried out
at the National Energy
Laboratory of Hawaii
(NELHA) at Keahole
Point.
The first real
breakthrough was in
1979 with the successful
operation of ‘Mini-OTEC’,
a 50 kWe closed-cycle
demonstration plant,
becoming the worlds first
net power producing
OTEC plant.
History Continued
 1974- United States
became involved in OTEC
research
 Natural Energy Laboratory
of Hawaii Authority was
established.
 Has become one of the
world's leading test facilities
for OTEC technology.
 1980- two laws enacted to
promote commercial
development of OTEC
technology.
 Ocean Thermal Energy
Conversion Act, and the Ocean
Thermal Energy Conversion
Research, Development, and
Demonstration Act .
 Natural
Energy Laboratory, Hi.
NELHA, Hawaii
In 2001 NELHA established an
ocean energy park at Keahole Point.
 It uses cold deep seawater that is
pumped to the surface to produce
energy, air-conditioning,
desalination, fish farming and
agriculture. Additional OTEC
projects are being considered for
Hawaii.
 In 2006 , the Kailua-Kona opencycle OTEC plant operated by
PICHTR generated 225 kW gross of
electricity and 104 net.
 This plant is part of a $12-million,
five year project, with a majority of
the power used by NELHA.

NELHA,
Hawaii
Over 9,000 gallons/minute of seawater pours in from 13
upright white plastic pipes.
 As the pressure drops to that of 70,000 feet, the 72oF water
goes ballistic in the vacuum chamber.
 As less than 0.5% of the incoming ocean water becomes
steam, huge amounts of water must be pumped through the
plant to create enough steam to run the large, low pressure
turbine.
 The quantities of water needed limits the open-cycle system of
no more than 3MW of gross power, as the bearing support
system for larger turbines is not practical.
 In comparison, a large nuclear reactor can produce 1,000 MW.
 The real advantage of this system is the by-products such as
large quantities of desalinated water, air conditioning and
ocean minerals.

Location: Cayman &
Puerto Rican Trenches
The Cayman Islands , Cuba,
Jamaica, and all of the islands off
of the Puerto Rican Trench are all
ideal locations for OTEC
technology, These are the
deepest parts of the Caribbean,
over four miles deep.
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For a shore-based plant, an additional requirement is
topography that allows access to very deep water (1km or
deeper) directly offshore, conditions that exist at certain
tropical islands, coral atolls, and a limited number of
continental sites.
In the United States, potential sites include Hawaii, Puerto
Rico, and the continental shelf off the Gulf of Mexico.
Ocean Thermal Energy Conversion
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OTEC plants can either be
built onshore or on offshore
floating platforms.
Energy can be transported
via seafloor cable, just a
short distance from platform
to grid.
The OTEC platforms could be
located in shallow water,
right on the edge of the
trench, which is a huge
escarpment like structure
that plunges straight down.
Proposed Lockheed OTEC
System
More Potential OTEC Sites
The OTEC platforms could be located in shallow water, right on
the edge of the trench, which is a huge escarpment like
structure that plunges straight down.
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The South Pacific and Molokai, Hawaii.
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American Territories such as Guam, American Samoa and
US Gulf Coastal areas.
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Caribbean islands adjacent to deep-sea trenches.
Military and security uses of large
floating plant -ships with
major life-support systems
such as power, desalinated
water, cooling and aquatic
food.
Ships such as this could save
many lives and relieved great
suffering in natural disaster
areas such as the 2004 EQ/T
in Banda Ache, Thailand,
Indonesia, and Sri Lanka.
OTEC Grazing plant-ship.
OTEC Efficiency
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The thermal gradient gives OTEC a typical energy
conversion of 3 to 4%, whereas conventional oil or coal
fired steam plants, often have temperature differentials of
500oF, yielding thermal efficiencies of 30 to 35%.
Remember, the greater the difference between hot and cold
temperatures, the greater the efficiency of the energy
conversion system.
So to compensate for its low thermal efficiency, OTEC has
to move a tremendous amount of water.
It takes 20 to 40% of the power generated to pump the
water through intake pipes in and around an OTEC system.
This is why, almost 100 years after the idea was first
conceive, OTEC researchers are still striving to develop
plants that will consistently produce more energy than is
needed to run the pumps, and that will operate in the
corrosive marine climate, to justify the development and
construction.
Ocean Thermal Energy Conversion
Benefits of OTEC:
 Dependable constant
energy source
 Fresh drinking water
 Air conditioning
 Refrigeration
 Sea salt & minerals
 Agricultural and
Maricultural uses
Drawbacks:
 Still in the
developmental /
experimental stage.
Benefits
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Promotes competitiveness and international trade
Enhances energy independence and energy security
Promotes international sociopolitical stability
Reduce greenhouse gas emissions resulting from
burning fossil fuel
In small island nations promotes self-sufficiency
minimal environmental impacts
improved sanitation and nutrition
Economic Benefits
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Helps produce fuels such as hydrogen, ammonia, and
methanol
Produces base load electrical energy
Produces desalinated water for industrial,
agricultural, and residential uses
Provides air-conditioning for buildings
Provides moderate temperature refrigeration
Potential to provide clean, cost effective electricity for
the future
Desalinated Water
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Desalinated water can be produce from
either open-cycle or hybrid OTEC plants.
In an open-cycle plant, the warm water,
after being vaporized, can be re-condensed
while being kept separate from the cold
seawater, leaving behind the salt and
providing a source of desalinated water
fresh enough for municipal or agricultural
use.
The condensate is relatively free of
impurities and can be collected and sold to
local communities where freshwater supplies
are limited.
How OTEC is used

Aquaculture is the
cultivation of aquatic
organisms.
Aquaculture, also
known as
aquafarming, implies
the cultivation of
aquatic populations
under controlled
conditions.
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Cold, deep seawater brought up by OTEC
pipes is nutrient-rich and parasite and free,
and can be pumped into onshore ponds
producing algae or other products in a
controlled system.
At the National Energy Laboratory of Hawaii
(NELHA), private companies have already
profited from raising lobsters, flounder, and
high-protein algae in mariculture ponds fed
by the cold water.
This cold water has also been used to grow
temperate crops such as strawberries in
Hawaii's tropical climate.
The tremendous volume of water pumped
required to run an OTEC plant, when
funneled out to a mariculture facility will
reduce disease and contamination in
growing ponds, enabling marine life, such
as shrimp, to be grown in higher densities.
The low-cost refrigeration, can also be used
to upgrade or maintain the quality of
indigenous fish, which tend to deteriorate in
hot, tropical climates.
Mariculture
How OTEC is used
The cold seawater delivered to a plant can
be used in chilled-water coils to provide
air-conditioning for buildings
 Also supports chilled soil agriculture.

Seawater Air
Conditioning
In tropical locations, air conditioning is one of the largest
uses of electricity in homes and businesses.
 Seawater air conditioning (SWAC) pumps cold seawater
(5oC; 41oF) to a station via a deep-sea pipeline to a cooling
station on shore, where it is used to cool freshwater, which
is then piped to a building’s air conditioning system via
chilled-water coils.
 The seawater is returned to the ocean through a pipe and
diffuser system.
 Currently, both of the two main buildings at the National
Energy Laboratory of Hawaii Authority (NELHA) in KailuaKona on Hawaii are effectively air conditioned by cold
seawater pumped through OTEC pipes.

References
"Ocean Thermal Energy Conversion." Energy Savers. 30 DEC 2008. U.S.
Department of Energy. 3 May 2009
<http://www.energysavers.gov/renewable_energy/ocean/index.cfm/mytop
ic=50010>.
"Ocean Thermal Energy Conversion." National Renewable Energy Laboratory.
3 May 2009 <http://www.nrel.gov/otec/what.html>.
"Ocean Thermal Energy Conversion." Wikipedia. 20 Apr 2009. Wikimedia
Foundation, Inc.. 3 May 2009
<http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion>.
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