Ocean thermal energy conversion (OTEC) harnesses the temperature difference between warm surface waters and cold deep ocean waters to generate electricity. The tropical oceans have about a 20°C difference between these waters that can power an OTEC system. OTEC systems pump warm surface water and cold deep water through a heat exchanger and turbine to produce electricity with minimal environmental impact. While capital costs are high currently, OTEC has potential for baseload renewable power due to the constant solar heating of ocean waters.

1. Ocean thermal energy
conversion

2. INTRODUCTION
 What do you mean by renewable energy?
Renewable energy is energy derived from natural sources that are replenished at a higher
rate than they are consumed. Sunlight and wind, for example, are such sources that are constantly being
replenished.
 What are the types of renewable energy?
Solar Energy, Wind Energy, Geothermal Energy, hydro Power, OCEAN ENERGY, Bioenergy.
 There are different forms of Ocean energy: wave
tidal
marine currents
thermal gradient.
 Ocean thermal energy is created by solar energy - when ocean water absorbs solar radiation.

3. OCEAN THERMAL ENERGY CONVERSION
 Especially in the tropical waters, the difference between temperatures at the surface and that
at the bottom at around 1000m water depth is around 20°C.
• This difference in temperature or thermal gradient can be used to harness energy and is called
OTEC in short.
 A minimum temperature of 20°C is required between source and sink so that heat engine
can effectively operate to generate power.
 Because the oceans are continually heated by the sun and cover nearly 70% of the earth surface,
this difference contains a vast amount of solar energy which could potentially be tapped for
human use.

4.  Deeper into the ocean, the water becomes colder. A huge amount of cold water
exists at depths around 1000m, which is due to accumulation of ice-cold water
that has melted from the polar regions.
o The two bodies of warm water from the surface and cold water from the deep
can be used to run the OTEC cycle for generating the power.
TEMPERATURE PROFILE FOR INDIAN WATERS
 The sun warms the surface sea water to an extent that all the energy is captured in a region upto 100m in
thickness near the surface. This is called 'mixed layer' since wind and wave actions cause the temperature and
salinity to be uniform in this layer.

5. Components of an OTEC system
 Ocean water
 Turbine
 Heat exchanger
o Sea water pump
• Condenser
 Platform
 Station keeping / mooring
∞ Control system

6. OTEC Cycle and system
Can be classified into two types based on cycle :-
Open cycle: In this, the working fluid is vented out after use.
Closed cycle: refrigerate is re-circulated in a closed loop to
vaporize and drive the turbine.
Hybrid cycles combine features of both open and closed cycle
systems.
Can be classified into two types based on location :-
 Land based plant
 Shelf based plant
 Floating plant
o submerged plant

7. Open cycle OTEC power plant :
Cold water from depth of the ocean [50 C ]
Warm water from ocean surface [ 250 C ]
Evaporator
0.2 bar
>1000 m
Warm water
in Warm water discharge
Turbine
Condenser
Low pressure stream of 0.2 bar Generator
Electrical
output
Cold water
pump
Fresh
water
Cold water
in
Cold water
out
Vacuum pump
Dissolved
gases

8. Closed cycle OTEC power plant :
Cold water from depth of the ocean [50 C ]
Warm water from ocean surface [ 250 C ]
Evaporator
1.2 km
Warm water
in Warm water discharge
Turbine
Condenser
Low pressure stream Generator
Electrical
output
Cold water
pump
Fresh
water
Cold water
in
Cold water
out
Ammonia
Storage tank
Pump

9. Closed cycle
 The basic requirements for working fluid in a closed system are:
Low boiling point.
Low volume of the fluid per kW of power produced.
High heat transfer characteristics.
Environmental acceptability.
Acceptable cost.
 Most refrigerates could be used in an OTEC cycle.
o Ammonia is popularly considered for a closed loop OTEC cycle.
 Thermodynamically, for converting thermal energy to mechanical energy, cycles used are
Rankine and Kalina cycles.
Uehara cycle developed in Japan also is important.

10. OTEC SYSTEM APPLICATION
 Electricity Production
 Desalinated water
 Refrigeration and Air-Conditioning
 Mineral Extraction

11. OTEC SYSTEM APPLICATION
Electricity Production:
Two basic OTEC system designs have been demonstrated to generate electricity: closed
cycle and open cycle.
Desalinated water:
Desalinated water can be produced in open- or hybrid-cycle plants using surface
condensers.
A surface condenser can be used to recover part of the steam in the cycle and to reduce the
overall size of the heat exchangers.
One way to produce large quantities of desalinated water without incurring the cost of an
open-cycle turbine is to use a hybrid system.
In a hybrid system, desalinated water is produced by vacuum flash distillation and power is
produced by a closed cycle loop.

12. OTEC SYSTEM APPLICATION
Refrigeration and Air-Conditioning:
The cold [5°C (41°F)] seawater made available by an OTEC system creates an opportunity to provide large
amounts of cooling to operations that are related to or close to the plant.
The low-cost refrigeration provided by the cold seawater can be used to upgrade or maintain the quality of
indigenous fish, which tend to deteriorate quickly in warm tropical regions.
The cold seawater delivered to an OTEC plant can be used in chilled-water coils to provide air-conditioning
for buildings
Mineral Extraction:
The ocean contains 57 trace elements in salt dissolved in solution.
The Japanese recently began investigating the concept of combining the extraction of uranium dissolved in
sea water with wave-energy technology.
They found that developments in other technologies were improving the viability of mineral extraction
processes that employ ocean energy.

13. What is OTEC efficiency
OTEC converts a low-grade heat source into electricity by using a thermodynamic cycle.
The efficiency of the cycle is determined by the Carnot cycle and is 7-8%,which is for an ideal
reversible heat engine.
But heat exchangers, turbine, pumps, generator, etc. contribute to large losses and
Hence efficiency is much lower than the ideal one.

14. EFFICEIENCY OF OTEC SYSTEM
The conversion efficiency of an OTEC system is given by the expression:
Efficiency = T1 - T2 / T1 * 100
Where,
 T₁ = temperature of warm water in degree kelvin
 T2 = temperature of cold water in degree kelvin
The efficiency of heat engine working between two temperature limit cannot be more that of Carnot cycle
efficiency (n). Due to this the overall efficiency is obtained by multiplying a relative efficiency factor (E.F.) to conversion
efficiency (n).
The overall efficiency of an OTEC system is given by,
Efficiency OTEC= Efficiency * E.F.
= T 1 -T 2/T 1 * E.F.*100
Relative efficiency factor EF is about 0.4 to 0.6.

15. Determine the efficiency of an OTEC plant if warm water temperature is 27°C and cold water
temperature at a depth of 1000 m is 7°C. Assume the relative efficiency factor of 0.5 .
Solution:
T₁ = temperature of warm water = 27°C
= 27 + 273 = 300 K
T2 = temperature of cold water = 7°C= 7 + 273 = 280 K
Efficiency factor =0.5
Efficiency OTEC= T 1 -T 2/T 1 * E.F.*100
= (300 - 280)/300 * 0.5 * 100
=3.33%
PROBLEM RELATED TO EFFICEIENCY OF OTEC SYSTEM

16. Advantage Of OTEC Disadvantage of OTEC
 Renewable energy.
 Clean energy.
 Reliable.
 Environmental friendly.
 Low maintenance.
 Independent of weather.
 Unlike other forms of solar energy, the output of
OTEC shows very little daily or seasonal variation.
 Capital investment is very high.
 Locality of production.
 High commercing cost.
 Interfere with navigation.
 Slight temperature difference.
 Large size turbine with expensive liquid.
 Harmful on marine life.
 Conversion efficiency is very low about 3-4% due to the
small temperature difference between the surface water
and deep water.

17. HISTORY OF OCEAN THERMAL ENERGY CONVERSION
The OTEC concept was first proposed in the early 1880s by the French engineer Jacques-Arsène d'Arsonval
His idea called for a closed-cycle system.
Jacques-Arsène d'Arsonval First article about to OTEC OTEC plant on the ship “ Tunisise ” off
the Brazil coast ( 1935 )

18. OTEC test facility at keahole point kona ,
Hawaii ( estd. 1974)
Pipes used for OTEC plant in tamil nadhu in
2002
The floating OTEC plant off the TN coast
Construction of the OTEC plant at
kume island Okinawa in 2013.
Map representing the thermoclines
across the oceans

19. Future of OTEC
Upcoming project and locations:
 The Bahamas – US
 Hainan island – China
 Hawaii – US Japan
 Virgin islands – US
 Kiribati
 Andaman and Nicobar island – India
 Martinque – France
 Reunion island -france