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					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?


   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 re-
    condense 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)
   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




 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
   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.
 1981- Became operational                              Japan

 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
 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, Hi.
 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 .
    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 open-
  cycle 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.

   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
   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.
      The South Pacific and Molokai, Hawaii.
     American Territories such as Guam, American Samoa and
      US Gulf Coastal areas.
     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
   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

   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
   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
   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.
   Cold, deep seawater brought up by OTEC
    pipes is nutrient-rich and parasite and free,
    and can be pumped into onshore ponds
                                                    Mariculture
    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.
        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 Kailua-
    Kona 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>.
    Striving for a Sustainable Future:


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