Ocean thermal energy conversion (OTEC) uses the temperature difference between warm surface waters and cold deep waters to generate electricity. OTEC works by pumping warm surface water to heat a working fluid like ammonia in a heat exchanger, vaporizing it to drive a turbine. Cold deep water is then pumped up to condense the working fluid back into a liquid. For significant power production, the temperature difference must be over 20°C. OTEC is a clean energy source that does not contribute to climate change like fossil fuels and can also produce fresh water. However, OTEC plants face challenges from technical difficulties maintaining equipment in the corrosive ocean environment and achieving high efficiency from the small temperature differences available.
2. What Is OTEC ?
e Ocean thermal energy conversion (OTEC) is a method for generating electricity
which uses the temperature difference that exists between deep and shallow
waters.
e 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
e Temperature difference between warm surface water and cold deep water must
be >20°C (36°F) for OTEC system to produce significant power.
3. Background Information
e 60 million km2. (23 million miles2) of tropical seas absorb a tremendous amount of solar
radiation.
e Heat content equal to about 250 billion barrels of oil.
e 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.
4. Why OTEC ?
e A clean energy source:- it delivers an environment friendly solution that
produces electricity without the expense and price volatility of fossil fuels.
e Improved technology: - the qualitative analysis of technical readiness of OTEC by
experts of US national oceanic and atmospheric administration (NOAA) suggest
that a<10MW floating, closed cycle OTEC facility is technically feasible using
current design, manufacturing, deployment technics and materials.
e Need for possible water: - large OTEC power plant can be designed to coproduce
120 million litres of fresh water daily. The OTEC power cycle moves about four
cubic kilometre of high nutrient deep water per year (1 sq. km 11.5 m deep each
day. Enough to grow 70 tons of shellfish meat per day).
e Increased awareness of the effects of climate change;- OTEC is carbon neutral
and does not contribute to climate change by burning fossil fuel such as coal, gas
and oil.
6. Initial Projects
e 1881- Jacques Arsene d’Arsonval, French physicist, proposed tapping the thermal
energy of the ocean.
e 1930- Georges Claude, d’Arsonval’s student, built the 1st OTEC plant in Cuba.
e 1935- Claude constructed another plant aboard a 10,000 ton cargo vessel off the
coast of Brazil.
e Weather & waves destroyed both plants before they could become net power
generators.
e 1956- French scientists designed another OTEC plant for Abidjan, Ivory Coast,
West Africa.
e The plant was never completed due to reduced energy costs. Large amounts of
cheap oil became available in the 1950’s.
7. First OTEC In Operation
e 1970- Tokyo Electric Power Company successfully built & deployed a 100 kW
closed-cycle OTEC plant on the island of Nauru.
e 1981- Became operational .
e Produced about 120 kW of electricity .
e 90 kW was used to power the plant & the remaining electricity used to power a
school & several other places on Nauru.
e Set a world record for power output from an OTEC system where the power was
sent to a real power grid.
8. Types Of Cycles Used
1. Open Cycle
2. Close fCycle &
3. Hybrid Cycle
9. Open Cycle
e In open-cycle OTEC, the sea water is itself used to generate heat without any kind of
intermediate fluid.
e At the surface of the ocean, hot sea water is turned to steam by reducing its pressure .water that
leaves the OTEC plant is pure and salt-free.
10. Close Cycle
e In closed-cycle OTEC, warm surface seawater
heats a working fluid, such as ammonia, with a
low boiling point, such as ammonia, which flows
through a heat exchanger (evaporator).
e The ammonia vapor expands at moderate
pressures turning a turbine, which drives a
generator which produces energy.
11. Hybrid Cycle
A hybrid cycle combines the features of the closed- and open-cycle systems. In a hybrid, warm seawater enters a
vacuum chamber and is flash-evaporated, similar to the open-cycle evaporation process. The steam vaporizes
the ammonia working fluid of a closed-cycle loop on the other side of an ammonia vaporizer. The vaporized fluid
then drives a turbine to produce electricity. The steam condenses within the heat exchanger and
provides desalinated water.
12. Some Projects
e Hawaii :- 10-MW closed cycle OTEC pilot system which will become operational
in Hawaii. This effort was cancelled when the Navy determined that the system
was not viable.
e Hainan :- 10 megawatt plant off the coast of southern China to provide power for
a planned resort on Hainan island.
e Japan :- The main aim is to examine the expected fluctuation of electricity supply
caused by changes in weather, season, and sea temperature. The testing and
research will be conducted with the support of Saga University until the end of
2014. The plant installation was finished in March and the first trial run was held
on the 30th of March.
13. OTEC in India
e About 1.5 x 106 square kilometeres of tropical water in the
Exclusive Economic Zone around India with a power density of
0.2 MW/km2. Apart from this, attractive OTEC plant locations
are available around Lakshedweep, Andaman & Nicobar Islands.
The total OTEC potential around India is estimated as 180,000
MW considering 40% of gross power for parasitic losses. This
indicates the promise of OTEC for India and points out the
urgent need to develop OTEC technology.
e The Indian OTEC programme started in 1980 with the proposal
of General Electrical Co. of USA to install a 20 MW plant off the
Tamil Nadu coast and subsequently in 1982.
e A preliminary design was also done in 1984 for a 1 MW closed
Rankine Cycle floating plant with ammonia as working fluid.
e Early 1997, DOD, Government of India proposed to establish a 1
MW gross OTEC plant in India.
e In January 2008 trial production of 1MW project has been
completed.
Image of 1 mw plant in Tamil Nadu
14. Floating Plants
e They are not tied to a land base and therefore require
long and expensive cables that would get tangled and
need repair.
e If the base was not kept stable, the cold water pipe
might break, especially during high seas and storms.
e 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.
e 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.
15. Shelf-Based Plants
e OTEC plants can be placed on the continental shelf, down to depths of no more
than 100 meters.
e The same kind of construction that is used to build offshore oil rigs would be
used to build shelf-based plants.
e These plants would have problems with product delivery and the stressors of the
open ocean.
e Working these plants in water 100 meters deep also presents problems and
these plants are more expensive than the land-based plants.
16. Land Based Plants
e Have both advantages and disadvantages over shelf based
and floating plants
e 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
e They require less maintenance and can be installed in areas
that are sheltered from storms which could possibly destroy
the plant.
e In addition, land based plants can support mariculture using
desalinated water.
e 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.
e 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.
17. OTEC Efficiency
e 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%.
e Remember, the greater the difference between hot and cold temperatures, the
greater the efficiency of the energy conversion system.
e So to compensate for its low thermal efficiency, OTEC has to move a
tremendous amount of water.
e It takes 20 to 40% of the power generated to pump the water through intake
pipes in and around an OTEC system.
e 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]
PRESENTED BY:-
Raj Ranjan Gupta](https://image.slidesharecdn.com/otec-rajpptx-160219125607/85/Otec-raj-pptx-1-320.jpg)
