This document discusses Ocean Thermal Energy Conversion (OTEC) technologies. OTEC uses the temperature difference between warm surface seawater and cold deep seawater to produce electricity. There are three main types of OTEC systems - open cycle, closed cycle, and hybrid cycle. OTEC has advantages such as steady base load power production and byproducts like fresh water. However, it also has disadvantages like low efficiency due to small temperature differences and challenges associated with operating in an ocean environment. The document provides examples of OTEC applications and references for further information.

1. G.L BAJAJ INSTITUTE OF TECHNOLOGY &
MANAGEMENT, GR. NOIDA
DEPARTMENT OF MECHANICAL ENGINEERING
Presented By
Mr. V.S. SRIVASTAV
(Asst. Prof. )
1
Topic – Ocean Thermal Energy Conversions

2. OVERVIEW
• Introduction
• Working
• Types
• Advantages and disadvantages
• Applications
• References
2

3. Introduction [1]
• Ocean Thermal Energy Conversion (OTEC) technologies use the
temperature difference between warm seawater at the surface of the ocean,
and cold seawater at between 800–1000 metres (m) depth to produce
electricity.
• It is also a form of Solar energy.
• Ocean Thermal Energy Conversion (OTEC) projects have been around
since the 1970s.
• Open Cycle OTEC uses seawater as the working fluid, Closed Cycle OTEC
uses mostly ammonia.
• The efficiency of the Carnot cycle is very low (maximum 7%), this does not
impact on the feasibility of OTEC as the fuel is ‘free’.

4. Working Procedure
Fig:1 Open Cycle OTEC[5]

5. Working Principle [2]
• The vertical temperature distribution in the open ocean can be
represented as two layers separated by an interface. The upper layer is
warmed by the sun and mixed to depths of about 100 m by wave motion.
• The bottom layer consists of colder water formed at high latitudes. The
interface or thermocline is sometimes marked by an abrupt change in
temperature but more often the change is gradual. This implies that there
are two reservoirs providing the heat source and the heat sink
required for a heat engine.
• A practical application is found in a system designed to transform the
thermal energy into electricity. This is referred to as OTEC for Ocean
Thermal Energy Conversion.

6. Working Principle continue
• Generally operating with temperature differences of around 20
degrees centigrade (°C) or more. Considering that temperature
levels at one kilometre depth are relative constant at about 4°C,
this means that OTEC is particularly suitable for mean surface
temperatures around 25°C.
• This small temperature difference is converted into usable electrical
power through heat exchangers and turbines.
• First, through a heat exchanger or a flash evaporator warm seawater
issued to create vapour pressure as a working fluid.
• The vapour subsequently drives a turbine-generator producing
electricity.
• At the outlet of the turbine, the working fluid vapour is cooled and
condensed back into liquid by colder ocean water brought up from
depth or the sea bed. A heat exchanger is also used for this process.

7. Efficiency of OTEC
• The efficiency of heat engine is limited to Carnot engine efficiency,
which is given by
η = (T1 - T2) / T1
• where T1 is the source temperature in Kelvin and T2 is the sink
temperature in Kelvin.
• In case we take T1 = 25°C and T2 = 5°C, we have
η = 6.7% ~ 7%

8. Types
1. Open Cycle OTEC
2. Close Cycle OTEC
3. Hybrid Cycle OTEC

9. Open Cycle OTEC[6]
Fig:2 Open Cycle OTEC[3]
Warm water from the top surface is
evaporated to obtain low pressure steam by
using a flash evaporator maintained at
partial vacuum as water can evaporate at the
lower temperature when pressure is lower
than atmospheric pressure. The low pressure
steam obtained from flash evaporator is
expanded in a turbine to extract mechanical
energy. The steam after energy removal in
turbine is condensed into water in a
condenser which is cooled by cold water
drawn from the depths in the ocean.
Parts Name:
(Evaporator, Pump, Generator, Turbine etc.)

10. Close Cycle OTEC Plant[6]
Fig:3 Close Cycle OTEC[4]
In the closed cycle, warm surface water is
used to evaporate a low boiling point
refrigerant (ammonia or Freon) and
refrigerant vapour is made to flow through
the turbine to extract energy. The vapour
coming out from the turbine after
performing work is cooled and condensed
in a condenser cooled by cold water
pumped from the ocean depths.

11. Hybrid or Mixed Cycle OTEC Plant
• Hybrid systems combine both the open
and closed cycles
• where the steam generated by flash
evaporation is then used as heat to drive
a closed cycle.
• First, electricity is generated in a closed
cycle system as described above.
Subsequently,
• the warm seawater discharges from the
closed-cycled OTEC is flash
• evaporated similar to an open-cycle
OTEC system, and cooled with the cold
water discharge. Fig:4 Hybrid or Mix Cycle OTEC[4]

12. Advantage of OTEC [6]:
• The plant can supply steady power without any fluctuation in all the vagaries of weather.
• The power output does not vary from season to season.
• The plant needs usual thermodynamic devices and equipment, such as turbine, heat exchanger and
condenser.
• The useful by-products from the OTEC plant are desalinated water and nutrients from marine
culture.
• The plant can be constructed on shoreline or on floating platform.

13. Disadvantage of [6]:
 The design, operation and maintenance of flash evaporator, pump and turbine in
the open system are problematic.
 Long-distance cable to transmit power to shore is required.
 The plant has to withstand severs ocean conditions and storms. The plant
equipment has to resist the corrosive effects of ocean water.
 The plant has to remove algae growth on a regular basis.
 The whole plant has to be constructed on floats. Equipment has to be installed at a
great depth to reach the cold water level.
 As low temperature difference exists in upper surface and deep water, thereby
plant has a very low efficiency in converting ocean thermal energy.

14. The environmental impacts due to construction of
OTEC plant are as follow[6]:
• The marine life (eggs, larvae and fish) can be destroyed due to water
circulation.
• The plant may affect ecosystem and impact coral. It can also influence
ocean currents and climate.
• The plant releases a large quantity of cold water into warmer surface
environment which may adversely affect the marine life.
• The carbon dioxide dissolved in warm water is released to the atmosphere
in open cycle, which has greenhouse effect on environment.
•

15. Applications[7]
• The cold sea water may have applications for open-ocean mariculture.
Artificial upwelling of deep water has been suggested as a method of
creating new fisheries and marine biomass plantations. Should
development proceed, open-ocean cages can be eliminated and natural
feeding would replace expensive feed, with temperature and nutrient
differentials being used to keep the fish stock in the kept environment.

16. References
1. https://www.irena.org/documentdownloads/publications/ocean_ther
mal_energy_v4_web.pdf
2. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.666.6227
&rep=rep1&type=pdf
3. https://images.app.goo.gl/pyGS9ZnDVx8RKbR5A
4. http://earthsci.org/mineral/energy/wavpwr/wavepwr.html
5. https://images.app.goo.gl/fZ6AEsQaF73edHeWA
6. NON-CONVENTIONAL ENERGY RESOURCES, By - G.S.
Sawhney, PHL learning publication -2012
7. file:///C:/Users/Vishal%20Srivastav/Desktop/OTEC3.pdf