Ocean Thermal Energy

Conversion (OTEC)
• The Conversion of solar energy as heat in the
ocean into electrical energy by making use of the
temp. difference between the warm water and the
colder deep water.
• The Facilities proposed for achieving the
conversion are commonly referred to as OTEC
Plants .
• Since the ocean waters are heated by the sun, they
constitute a virtually in-exhaustible source of
energy . Unlike Direct solar energy , the ocean
energy is available continuously rather than only in
daytime.
• The operation of the OTEC plant is based on a well
established physical(thermodynamic)principle . If a
heat source , is available at a higher temperature
and a heat sink at a lower temp. , it is possible in
principle , to utilize the temperature difference in a
machine or prime mover (Ex: Turbine) that can
convert part of the heat taken up from the source
into mechanical energy and hence into electrical
energy. The residual heat is discharged to the sink
at the lower temperature .In OTEC system , the
warm ocean surface water is the heat source and
the deep colder water provides the sink.
• The temperature gradient can be utilized in a heat
engine to generate power. This is called ocean thermal
energy conversion(OTEC) .OTEC may be considered
solar energy once removed . This energy form has very
low efficiency and has very high capital cost , because
the temperature difference is small even in tropics.
 Introduction

• Oceans cover more than 70% of Earth's surface, making them

the world's largest solar collectors.

• OTEC is a renewable energy technology that converts solar

radiation into electric power by use of world oceans.

• OTEC Process uses temperature difference between cold deep

water (5 ℃) & warm surface water (27 ℃) to power a turbine
to generate electricity.
 OTEC Working Principle

• This plant works on the principle of a closed Rankine

Cycle.

• Warm Water is used to evaporate working fluid like

Ammonia or halocarbon Refrigerant.

• Evaporated Fluid expands in a low pressure turbine, which

is coupled with a turbo alternator to produce electricity.
 OTEC Systems

• There are three types of electricity

conversion systems:

I. The Closed or Anderson, OTEC Cycle Power Plant

II. The Open or Claude OTEC Cycle Power Plant

III. Hybrid Cycle OTEC Power Plant.

 Closed-loop OTEC

• Closed cycle system use fluid with a low boiling point, such
as ammonia to power a turbine to generate electricity.
• In Closed cycle system , a liquid working fluid ,
such as ammonia or propane is vaporized in a
evaporator (or boiler); the heat required for
vaporization is transferred from the warm ocean
surface to the liquid by means of a heat exchanger.
The high-pressure vapour leaving the evaporator
drives an expansion turbine , similar to a steam
turbine that it is designed to operate at a lower inlet
pressure. The turbine is connected to an electric
generator in the usual manner. The low pressure
exhaust from the turbine is cooled and converted
back into liquid in the condenser.
• The Cooling is achieved by passing cold , deep
-ocean water , from a depth of 700-900 m or more ,
through a heat exchanger .The liquid working fluid
is then pumped back as high pressure liquid to the
evaporator , thus closing the cycle.
 Open-loop OTEC cycle

• Georges Claude Constructed first OTEC plant in 1929 in Cuba.

• The Claude Plant used an open cycle in which seawater itself plays
the multiple role of heat source, working fluid, coolant, & heat sink.
• In Open –cycle turbine system , water is the working
fluid .The warm surface water is caused to boil by
lowering the pressure , without supplying any additional
heat .The Low-pressure steam produced then drives a
turbine , and the exhaust steam is condensed by the deep
colder water and is discarded . A heat exchanger is not
required in the evaporator and direct contact between the
exhaust steam and a cold water spray makes a heat
exchanger as necessary in the condenser .
• On the other hand , because of the low energy content of
the low pressure steam , very large turbines or several
smaller units operating in parallel would be required to
achieve a useful electric power output.
 Hybrid OTEC cycle
•A Hybrid cycle combines the features of both the closed & Open
Cycle System.
• There are several variations on the standard OTEC
open-cycle system. One variation is the “Hybrid
cycle” which is an attempt to combine the best
features and avoid the worst features of the open
and closed cycles .Sea water is flash evaporated to
steam , as in the open cycle .The heat in the
resulting steam is then transferred to ammonia in
an otherwise conventional closed Rankine cycle
system.
 Basics of Tidal Power
• Tides are produced mainly by the gravitational
attraction of the moon and the sun on the water of
solid earth and the oceans. About 70 % of the tide
producing force is due to the moon and 30% to the
sun.The moon is thus the major factor in the tide
formation.
• Surface water is pulled away from the earth on the
side facing the moon , and at the same time the solid
earth
 Advantages of Tidal Power

• The biggest advantage of the tidal power is besides

being inexhaustible , it is completely independent
of the precipitation (rain) and its uncertainity.
• Tidal power generation is free from pollution , as it
does not use any fuel and also does not produce
any unhealthy waste like gases , ash , atomic
refuse.
• These power plants do not demand large area of
valuable land because they are on the bays(sea
shore)
 Limitations of Tidal power
• Sea water is corrosive and it was feared that the
machinery may get damaged.
• Construction in Sea or estuaries is found difficult.
• Cost is not favorable compared to the other sources
of energy.
• The Fundamental drawback to all methods of
generating tidal power is the variability in output
caused by the variations in the tidal range.
• The Tidal ranges is highly variable and thus the
turbines have to work on a wide range of head
variation . This affects the efficiency of the plant.
• It is feared that the tidal power plant would hamper
the other natural uses of estuaries such as fishing or
navigation.
 Advantages of Wave energy
• The wave energy has the advantage over wind or solar that
the energy has been naturally concentrated by accumulation
overtime and space and transported from the point at which
it was originally present in the winds .
• It is free and renewable energy source.
• Wave power devices do not use up large land masses unlike
solar or wind.
• These devices are relatively pollution free and, because they
remove energy from the waves ,leave the water in a
relatively placid (calm)state in their wakes .
 Disadvantages of Wave energy
• The major disadvantage of wave energy , as compared to
wind, is that the energy is available on the ocean. The
extraction equipment must operated in a marine
environment with all that implies in terms of maintenance
,construction cost, life time and reliability. The energy may
have to be transported a greater distance to shore.
• Wave, energy converters must be capable of withstanding
very severe peak stresses in storms.
• Wave energy conversion devices that have been proposed
are relatively complicated .
• Economic factors such as the capital investment, costs of
the maintenance , repair and replacement, as well as
problems of biological growth of marine organisms are all
relatively unknown and seem to be on the large side.
 An OTEC system application

• Hydrogen can be produced via electrolysis using

electricity generated by the OTEC process.

• Desalination
It’s produced in open & Hybrid cycle.

System analysis indicates that a 2 MW plant can produce 4300 cubic

meter desalination water each day.
 An OTEC system application

• Aquaculture
It reduces the financial & energy coasts of pumping large
volumes of water from deep ocean.
Deep ocean water contains high concentration of essential
nutrients that are depleted in surface water due to biological
consumption.

•Mineral Extraction
The ocean contains 57 trace elements in salt dissolved in
solution.
The Japanese investigated the possibility of extracting
Uranium.
 Advantages of OTEC

Warm surface sea water and cold water from the ocean from the
ocean depths replace fossil fuels to produce electricity.

OTEC plants will produce little or no carbon dioxide or other

polluting chemicals.

OTEC systems can produce fresh water as well as electricity. A lot

of fish & other nutritious sea-food will be collected in outlet flow.

OTEC can also be used to produce ammonia, hydrogen, aluminium,

chlorine and other chemicals.
 Disadvantages of OTEC

OTEC produced electricity at present would cost more

than electricity generated from fossils fuels at their current
costs.

No energy company put money in this project because it only had

been tested in a very small scale.

Construction of OTEC plants and lying of pipes in coastal waters

may cause localized damage to reefs and near-shore marine
ecosystem.
 Current operating Plants of OTEC
•In March 2013, Makai installed and operate a 100 kilowatt
turbine on the OTEC Heat Exchanger Test Facility, and connect
OTEC power to the grid.

•Okinawa Prefecture announced the start of the OTEC operation

testing at Kume Island on April 15, 2013. The plant consists of two
units; one includes the 50 kW generator while the second unit is
used for component testing and optimization.

•In July 2014, DCNS group partnered with Akuo Energy

announced their NEMO project. If successful, the 16MW gross
10MW net offshore plant will be the largest OTEC facility to date.