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Title : Methodology and Analysis Of Ocean Thermal Energy Conversion (OTEC) Technology
Author : Rajashekhar
Department Of Mechanical Engineering
University : M.S. Ramaiah Institute of Technology, Bengaluru
ISSN :
Volume: 01 Issue: 01
Publication Year: June 2026
ABSTRACT
Ocean Thermal Energy Conversion (OTEC) is an emerging renewable energy technology that utilizes the temperature difference between warm surface seawater and cold deep ocean water to generate electricity. This technology exploits the naturally occurring thermal gradient present in tropical oceans, where a minimum temperature difference of approximately 20°C exists throughout the year. OTEC systems operate through three principal cycles: open cycle, closed cycle, and hybrid cycle, each employing different working mechanisms to convert thermal energy into useful power. This paper presents a comprehensive methodology and analysis of OTEC technology, including its historical development, operating principles, plant classifications, and practical applications. The study examines the performance characteristics of various OTEC systems and discusses critical operational challenges such as biofouling and the presence of non-condensable gases that affect heat exchanger efficiency and overall plant performance. In addition to electricity generation, the potential of OTEC for freshwater production, refrigeration and air-conditioning, aquaculture, mariculture, and cold-water agriculture is evaluated. The environmental impacts, advantages, disadvantages, and economic aspects associated with OTEC implementation are also reviewed. Although current OTEC systems exhibit relatively low thermal efficiencies of approximately 3–4%, the vast and continuous availability of ocean thermal resources offers significant potential for sustainable energy production. Continued research, technological advancements, and large-scale demonstrations are necessary to improve system efficiency, reduce costs, and establish OTEC as a viable contributor to future global renewable energy portfolios.
Keywords: Ocean Thermal Energy Conversion (OTEC), Renewable Energy, Closed-Cycle OTEC, Open-Cycle OTEC, Hybrid OTEC, Biofouling, Desalination, Ocean Energy, Sustainable Power Generation.
1.0 INTRODUCTION TO OTEC
1.1 INTRODUCTION
Covering over 70% of the planet’s area, the Earth’s oceans could potentially be utilized as a source of virtually inexhaustible renewable energy. Ocean Thermal Energy Conversion (OTEC) is a method that employs naturally occurring temperature differences between warm surface water and colder deep seawater (Thomas, 1993). To be effective a minimum temperature difference between the ocean surface layers is 20oC . These temperature gradients exist primarily in specific tropical regions near the equator (Takahashi and Trenka, 1996).
Originally proposed by French Engineer Jacques Arsene d’Arsonval in 1881, OTEC is not a new technology. Since then many advancements have been made in the development of this technology. The three most common OTEC systems are: open-cycle, closed-cycle and hybrid cycle, all requiring a working fluid, condenser and evaporator within the system. These three systems all employ the thermodynamics of a working heat exchanger and use the temperature differences naturally occurring in the ocean as the driving force.
Concerns with efficiency losses due to biofouling, system power requirements and heat exchanging systems have lead to exploration through case studies and analysis. While OTEC systems have been studied since 1881 there have been few full-scale implementations. There are still, however, a number of studies being conducted, especially in Japan, regarding the implementation of this renewable large scale technology.
1.2 WHAT IS OTEC?
OTEC, Ocean Thermal Energy Conversion is an energy technology that converts solar radiation to electric power. OTEC systems use the ocean’s natural thermal gradient, consequently the temperature difference between the warm surface water and the cold deep water below 600 meters by about 20 C, an OTEC system can produce a significant amount of power. The oceans are thus a vast renewable resource, with the potential to help us produce billions of watts of electric power. The cold seawater used in the OTEC process is also rich in nutrients and it can be used to culture both marine organisms and plant life near the shore or on land. The total influx of solar energy into the earth is of thousands of times as great as Mankind’s total energy use. All of our coal, oil and natural gas are the result of the capture of solar energy by life of the past. There have been many projects for harnessing solar energy, but most have not been successful because they attempt to capture the energy directly. The problem with this is that huge collectors must be deployed to do this, and resulting in large costs. The idea behind OTEC is the use of all natural collectors, the sea, instead of artificial collector.
1.3 How does it work in eal life?
Warm water is collected on the surface of the tropical ocean and pumped by a warm water pump. The water is pumped through the boiler, where some of the water is used to heat the working fluid, usually propane or some similar material. If it is cooler you can use a material with a lower boiling point like ammonia. The propane vapour expands trough a turbine which is coupled to a generator that generating electric power. Cold water from the bottom is pumped through the condensers, where the vapour returns to the liquid state. The fluid is pumped back into the boiler. Some small fraction of the power from the turbine is used to pump the water through the system and to power other internal operations, but most of it is available as net power.
1.4 Literature review
The first known Ocean Thermal Energy Conversion (OTEC) system was proposed by a French Engineer Jacques Arsene d’Arsonval, in 1881 (Takahashi and Trenka, 1996). Recognizing the tropical oceans as a potential source of energy, through the natural temperature differences between the ocean’s surface water and deep water, D’Arsonval built a closed-cycle OTEC system, with ammonia as the working fluid, that powered an engine (Takahashi and Trenka, 1996). Ammonia was chosen as the best fluid available to accommodate the pressure differences between the two temperatures of water assuming that the temperature of the boiler was 30oC and the condenser was 15oC (Avery and Wu, 1994). The pressure differences in the OTEC system design was one of the challenges D’Arsonval had to overcome. Ammonia was selected because it had such a low boiling point allowing it to become vaporized by the small temperature gradients when pressurized by the pumps in the system. In similar cycles where the Rankine cycle is followed there is usually a higher pressure gradient in which to generate energy i.e. combustion driven engines. In the case of OTEC the temperature gradients are maximum 22oC therefore a working fluid that was able to change phases with such as small gradient was chosen. This proposed technology was never tested by d’Arsonval himself. A student of d’Arsonval named George Claude soon took on the challenge of properly designing and building a working OTEC system. Claude, however, took a different approach to the design. He stated that corrosion and biofouling of the heat exchanger in an OTEC system would be a problem in the closed-cycle design. Claude suggested using the warm seawater itself as the working fluid in an open-cycle, now better known as the Claude cycle (Avery and Wu, 1994). Claude next sought to prove his open-cycle theory at.
1.5 OTEC SYSTEM
The extraction of the potential energy available within the ocean is dependent upon the efficiency of the thermal system employed, including pumps, condensers and heat exchangers (Aftring and Taylor, 1979).
There are three types of cycles in OTEC System they are:
a) Open cycle.
b) Closed cycle.
c) Hybrid cycle.
1.5.1 OPEN CYCLE:
The open-cycle OTEC power plant, first proposed by Claude, uses the actual sea water as the driving fluid for the heat exchanger. It works by pumping the warm seawater into a low pressure (vacuum) evaporator chamber where the water boils. The evaporator chamber vacuum is maintained through a series of valves and careful maintenance to avoid atmospheric leakages. The vapor then drives a low pressure turbine to create electricity. Finally, the vapor is then cooled using deep seawater (Thomas, 1993).
The open-cycle system differs from the closed-cycle because instead of using ammonia or a specific low boiling point working fluid, it uses warm sea water as the working fluid. Overall the Claude cycle is similar to the Rankine cycle however it has several important differences. The first major difference is that it uses complex heat and mass transfer processes to flash evaporate the warm water in a pressurized system. It also is not essential that the effluent at the end stage matches the warm water heat becomes the working fluid in stage one. That is where the open – cycle concept comes into play.
The first stage of the open-cycle pumps the warm seawater into a pressurized called the evaporator. It is here where the water is introduced into the chamber through spray spouts. This maximizes the warm water surface area, allowing the water to have increased exposure to the reduced pressure. This causes the water droplets to boil and become vapor. This vapor, as in the closed-cycle, moves the turbine to produce electricity. The next stage in this cycle is the heat transfer to the cold seawater thermal sink, this stage is important for condensing the warm seawater. The final stage is the compression of the condensate back to atmospheric pressure. The water is then discharged.
Because the warm seawater is flash evaporated, it becomes desalinated and becomes pure fresh water. This is a major advantage to this type of system as it can provide fresh water to communities who are in shortage. Another major advantage is the fact that the working fluid is not a potential threat to the environment. However there are
several disadvantages to this type of system. The first one being that the system must be carefully sealed to prevent leakage into the system of atmospheric air. This would be detrimental to the system as it relies completely on the pressure gradient to flash evaporate the warm
1.5.2 CLOSED CYCLE:
The closed-cycle OTEC power plant was the first OTEC cycle proposed by D’Arsonval in 1881. This cycle uses a working fluid with a low-boiling point, usually propane or ammonia, in a closed flow path (Takahashi and Trenka, 1996). The working fluid is pumped into the evaporator where it is vaporized and in turn moves a turbine. Closed-cycle plants operate on a Rankin cycle. The first stage of this cycle is referred to as isentropic expansion, which occurs in the steam turbine. Isobaric heat rejection in the condenser follows. This stage the water vapor becomes a liquid and therefore the entropy is decreased. The next stage is the isentropic compression in the pump (Takahashi and Trenka, 1996). During this step, the temperature increases due to the higher pressure. The boiler then supplies isobaric heat causing the working fluid to vaporize. In an OTEC system the warm sea water would be pumped into the evaporator where the liquid ammonia would be pressurized. This pressure causes the ammonia to boil or become vapor. This works due to the ideal gas law that states that the temperature is directly proportional to the pressure; therefore if the pressure increases in a system, the temperature does too. The vapor ammonia then expands by traveling through a turbine. This turns the turbine making electricity. The ammonia vapor pressure at the outlet of the turbine is 7oC higher then the cold seawater temperature. The cold seawater is therefore brought up from the depths where heat exchange occurs and ammonia vapor is changed back into a liquid. The liquid ammonia is then pressurized by a pump started the cycle once more (Thomas, 1993). Rankine cycles, in theory, are able to produce non-zero net power due to the fact that less energy is required to increase the pressure of a liquid then are able to be recovered when the same fluid expands as a vapor. It is for this reason that phase changes are essential when producing
energy this way. The advantages of using a closed-cycle system are that it is more compact then an open-cycle system and can be designed to produce the same amount of power. The closed-cycle can also be designed using already existing turbo machinery and heat exchanger designs.
1.5.3 HYBRID CYCLE:
The Hybrid-cycle is one that has yet to be tested but uses principles from both the closed and open cycle OTEC systems to obtain maximum efficiency. The Hybrid cycle uses both seawater and another working fluid, usually designed using ammonia (Takahashi and Trenka, 1996). The fresh water is initially flashed into steam, similar to the closed-cycle; this occurs in a vacuum vessel. In the same vessel the ammonia is evaporated through heat exchange with the warm water. The ammonia is then physically mixed with the warm seawater in a two-phase, two substance mixture. The evaporated ammonia is then separated from the steam/water and re-condensed and re-introduced into the closed loop cycle. The phase change of the water/ammonia vapor turns a turbine producing energy (Thomas, 1993).
2.0 CLASSIFICATION OF OTEC PLANTS
There are two different kind of OTEC power plants, the Land based and the floating plant. They are:
2.1 Land-based power plant:
The land based pilot plant will consist of a building. This building will contain the heat exchangers, turbines, generators and controls. It will be connected to the ocean via several pipes, and an enormous fish farm (100 football arenas) by other pipes. Warm water is collected through a screened enclosure close to the shore. A long pipe laid on the slope collects cold water. Power and fresh water are generated in the building by the equipment. Used water is first circulated into the marineculture pond (fish farm) and then discharges by the third pipe into the ocean, downstream from the warm water inlet.This is done so that the outflow does not reenter the plant, since re-use of warm water would lower the available temperature difference.
2.2 Floating power plant:
Closed-cycle, open-cycle and hybrid-cycle
There are three types of OTEC designs: open cycle, closed cycle, and hybrid cycle. In an open cycle, seawater is the working fluid. Warm seawater is pumped into a flash evaporator where pressure as low as
0.03 bar cause the water to boil at temperatures of 22ºC. This steam expands through a low-pressure turbine connected to a generator to create power. The steam then passes through a condenser using cold seawater from the depths of the ocean to condense the steam into desalinised water.
In a closed cycle, a low boiling point liquid such as ammonia or another type of refrigerant is used as the working fluid in a Rankinecycle (common steam cycle). The heat from warm seawater flowing through an evaporator vaporizes the working fluid. The vapour expands through a turbine, then flows into a condenser where cold seawater condenses it into a liquid. A hybrid cycle is a combination of both closed and open cycles where flash evaporator seawater is used as the closed cycle working fluid.
2.3 Where can OTEC be used?
OTEC can be sited anywhere across about 60 million square kilometers of tropical oceans anywhere there is deep cold water lying under warm surface water. This generally means between the Tropic of Cancer and the Tropic of Capricorn. Surface water in these regions, warmed by the sun, generally stays at 25 degrees Celsius or above. Ocean water more than 1,000 meters below the surface is generally at about 4 degrees C. It would not be profitable to use an OTEC power plant in the Baltic Sea, because the average temperature is about 8-10ºC.
2.4 What can you use OTEC for besides produce electricity?
Fresh Water & Sea Food.
As the peoples of the world grown more prosperous, there will be a demand for higher quality food. Industry agriculture and commerce will require more fresh water. It is possible to use this resource to produce fresh water instead of producing electric power if there is a large ask for fresh water. The fresh water appearances when the cold water is put into contact with the vapour from the warm water stream in a large box. The vapours condense on the secondary heat exchangers, leaving the salt behind the warm water stream. The yield of fresh water from a 100 megawatt power plant would be approximately 33,000,000 cubic meter per year, comparable to flow of a medium-sized river. This is enough to support the city of Norrköping with water during a whole year. This water is completely salt-free, suitable for all agricultural, commercial, industrial and domestic uses. Besides desalinised water you also can get by-products as ammonia, methanol. Hydrogen can be electrolysed from seawater and mixed with nitrogen to from ammonia for easy transportation from the floating plants. OTEC plant it will stimulate the growth of all kinds of seafood. Green algae (phytoplankton) in the surface waters absorb soluble nitrogen and phosphorous compounds as the engage in photosynthesis. These green algae are either eaten by animals, or die from other causes. The waste from the grazers and their carcasses, combined with the bodies of dead phytoplankton sink slowly to the bottom, carrying with them most of the soluble nitrogen and phosphorous. This is released in deep water as the detritus decomposes. This results in the enrichment of the cold deep waters with essential mineral nutrients in much higher concentration than surface waters. When the spent cold waters are released near the surface by the action of a power plant, they become an artificient upwelling, similar in effect to the great natural upwellings which are the world’s great fisheries. The reality of this phenomenon has been shown in several fish farms that have used cold bottom water as a medium. The amount of food that can be produced in this way is very large, larger in market value than the electric power produced by the plant.
2.5 How effective is an OTEC power plant?
Theoretical, it is possible to convert the energy in a 23-temperature difference at an efficiency of 7-8%. In actual practice, it is possible to do this at slightly more than 3% efficiency. This not influence that the amount of power available is small, or that power generated for this source need be expensive. This energy is equivalent to the same amount of water passing through a hydroelectric dam with a water height of 56 meters. (In other words, an OTEC plant needs to handle no more water than a hydroelectric plant of the same capacity.) This temperature difference is constantly renewed by the action of the sun and the ocean currents, and is therefore inexhaustible. The amount of water constantly available for this use is enough to provide at least
300 times Mankind's total power usage. One notice, the steam locomotives, which were used during the middle of the 19th century, had a thermal efficiency of only about 3%.
3.0 BIOFOULING
3.1 INTRODUCTION TO BIOFOULING:
When designing OTEC systems it is important to identify potential causes of reduced heat exchanger efficiency. One concern is the potential effect of biofouling within the cold and warm sea water pipes. Biofouling is the unwanted accumulation of algae, microorganisms, marine animals and plants on the surfaces of pipes and heat exchangers, The possibility that biofouling of the heat exchangers would quickly degrade OTEC performance was raised as a serious potential problem with OTEC (Avery and Wu, 1994). Biofouling is thought to be a limiting factor in the implementation of OTEC systems. Aftring and Taylor (1979) conducted a study from mid-July to the end of September 1977, on a large barge located 13 km north of Christiansted, St. Croix, set out to determine the relationship between heat exchanger efficiency and biofouling. Table 1 gives the conditions of the experiment that sought to reproduce the conditions of an actual OTEC power plant.After ten weeks of exposure to the open-ocean conditions of a typical OTEC heat exchanger system, the pipes were assayed for overall accumulation of biological material on the inner surfaces using plate counts (Aftring and Taylor, 1979). It was observed that bacterial populations were 107 cells/ cm2. The densities of other components were 10-27 µg/ cm2 for organic carbon, 1.5-3.0 µg/cm2 for organic nitrogen, 4-28 ng/ cm2 for adenosine 5’-triphosphate, 3.8-
7.0 ug/ cm2 for carbohydrates and 0.2-0.8 ng/ cm2 for chlorophyll (Aftring and Taylor, 1979). It was concluded in this particular project that the actual extent of the biofouling within an OTEC heat exchanger was found to be extremely low and that after 10 weeks of study the layer of biofouling was less then 1µm thick (Aftring and Taylor, 1979).Although this particular investigation concluded that there was no reason to believe biofouling would disrupt OTEC heat exchanger units, other similar investigations found otherwise. In the early 1978 the U.S. Department of Energy funded a program to investigate therelationship between biofouling in an OTEC heat exchanger and overall performance efficiencies. Three different locations were selected: Hawaii, the Gulf of Mexico and Puerto Rico (Avert and Wu, 1994). These studies concluded that biofouling would become a threat if not treated after 6 weeks of full operation. Biofouling treatment options were also investigated, including both chemical and physical methods to treat the OTEC systems. These efforts discovered that the injection of 70 ppb of chlorine for one hour each day effectively prevents the development of a biological film (Avert and Wu, 1994). In July of 1986 further investigations of heat exchanger test samples exposed to seawater to a 70 ppb chlorine treatment for one hour a day for more then 1000 days showed no significant reduction in heat transfer due to biofouling (Avert and Wu, 1994). These concentrations of chlorine would not be harmful to the aquatic environment as they are 5% of the amount the U.S. Environmental Protection Act allows to be released (Avert and Wu, 1994). Other treatment options including brushing and ultra sonic radiation were found to be effective, but were not as appealing as an easily designed chemical treatment option (Avert and Wu, 1994). Biofouling can also be reduced by zinc plating within the HWP (Thomas, 1993).
3.2 Effect of Non-Condensable Gases on the Heat Transfer Performance in a Condenser of an Open Cycle OTEC Power Station:
Open cycle – ocean thermal energy conversion systems (OC-OTEC) use warm surface seawater and convert it to steam via an evaporator in order to move a turbine to create electricity (Amano and Tanaka, 2006). The exhaust from the turbine is then condensed using cold seawater drawn from depths where the temperature is more then 20oC cooler then the surface water (Amano and Tanaka, 2006). These OC-OTEC systems are usually placed several meters above sea level so water discharge from the low-pressure system to the atmosphere is accomplished using gravity (Amano and Tanaka, 2006). However the seawater required for the system has to be pumped into the system and therefore the pump power must be high enough to overcome the pipe resistance (Amano and Tanaka, 2006). It is during this pumping of the seawater into the system that high volumes of dissolved, non-condensable gasses are introduced into the OC-OTEC system.
3.2.1 Dissolved, non-condensable gasses in the condenser:
Because the surface water of the ocean contains such a high concentration of non-condensable gas it has been identified as being in a practically saturated solution. OC-OTEC systems depend on this warm surface water to move a turbine, therefore the presence of non-condensable gasses in the condensers of these OTEC systems has become a major problem (Amano and Tanaka, 2006). It is very important to research and design efficient methods for the exhausting of this non-condensable gases originating in the warm surface water, for setting acceptable concentration limits, for estimating the net output of OC-OTEC, and for the design of evaporators and condensers (Amano and Tanaka, 2006). These high efficient power generation systems should also be combined with fresh water recovery units along with cold water recovery systems for air conditioning, cooling and aquaculture.
3.2.2. OC-OTEC Non-Condensable Gas Investigation:
In order to identify the relationship between efficiency OC-OTEC power units and non-condensable gases, a small-sized experimental condenser was developed by Masatsugu Amano and Tadayoski Tanaka. A series of experiments were preformed by investigating the mass balance when non-condensable gasses accumulated inside the condenser in steady state (Amano and Tanaka, 2006). Three major conclusions were obtained from their extensive testing. The first conclusion was that the main factor in the influence of the non-condensable gas condensation efficiency was not dependent on the total concentration of the gas in the entire condenser rather the concentration of non-condensable gas located near the surface of the condenser (Amano and Tanaka, 2006). The second conclusion was that the non-condensable gas concentration located at the surface of the condenser depended on the inflowing gas concentration. Therefore, higher efficiency could be achieved by reducing the concentration of noncondensable gas before it enters the evaporator (Amano and Tanaka, 2006). The final conclusion was that the temperature of the warm water must be increased for better operation of the heat exchanger. This could be achieved by having a higher flow rate of surface seawater into the evaporator, thus increasing the heat of vaporization (Amano and Tanaka, 2006). If this was implemented, it would mean that very large evaporators and condensers would be required.
4.0 USES FOR OTEC TECHNOLOGY / Methodology
4.1 INTRODUCTION TO USES FOR OTEC TECHNOLOGY:
OTEC systems are not just limited to just producing electricity and because of the unique design of these power stations are potentially available to tackle other ventures in combination with electricity to offset some of the expenses associates with OTEC.
It includes the followings:
• Fresh water production.
• Air conditioning and Refrigeration.
• Aquaculture and Mariculture.
• Coldwater Agriculture.
4.1.1 Fresh water production.
Desalination is just one of the effective potential products that could be produced via OTEC technology. Fresh water can be produced in open-cycle OTEC plants when the warm water is vaporized to turn the low pressure turbine. Once the electricity is produced the water vapor is condensed to make fresh water (Takahashi and Trenka, 1996). This water has been found to be purer then water offered by most communities as well it is estimated that 1 MW plant could produce 55 kg of water per second. This rate of fresh water could supply a small coastal community with approximately 4000 m3/day of fresh water (Takahashi and Trenka, 1996). This water can also be used for irrigation to improve the quality and quantity of food on coastal regions especially where access to fresh water is scarce.
4.1.2 Air conditioning and Refrigeration.
Once cold water pipes are installed for an OTEC power plant the cold water being pumped to the surface can be used for other projects other then to provide the working fluid for the condenser. One of these uses is air conditioning and refrigeration. Cold water can be used to circulate through space heat exchangers or can be used to cool the working fluid within heat exchangers (Takahashi and Trenka, 1996). This technology can be applied for hotel and home air conditioning as well as for refrigeration schemes.
4.1.3 Aquaculture and Mariculture.
Another possibility for taking advantage of OTEC plants is the use of the water pipes to harvest marine plants and animals for the purpose of food. This proposition is still under investigation however it is proposed that seawater life including salmon, abalone, American lobster, flat fish, sea urchin and edible seaweeds could be harvested for ingestion using the cold water pipes that would be readily available from the OTEC power plants (Takahashi and Trenka, 1996).
Mariculture is another possibility that is currently being researched that would take advantage of the cold deep ocean water being transferred to the oceans surface. This water contains phytoplankton and other biological nutrients that serve as a catalyst for fish and other aquatic populations (Takahashi and Trenka, 1996). This water could serve to increase native fish populations through the recycling of trace nutrients that would not be otherwise available.
4.1.4 Coldwater Agriculture.
Because the coastal areas suitable for OTEC are in tropic regions there is a potential to increase the overall food diversity within an area using the cold water originating from the deep ocean. It has been proposed that burying a network of coldwater pipes underground the
temperature of the ground would be ideal for spring type crops like strawberries and other plants restricted to cooler climates (Takahashi and Trenka, 1996). This would not only supply the costal populations with an increased variety of food but reduce the cost of transport of cooler climate foods that would otherwise have to be shipped.
5.0 EFFECT OF OTEC
5.1 Environmental Impacts.
Overall proposed OTEC technologies have many potential benefits to the environment. OTEC is a source of clean, renewable energy and harnesses the seawater for electricity generation which is an abundant and is almost unlimited. The use of OTEC also ensures that a reliable able and constant power output would be supplied as it is not depended on certain climate conditions or fossil fuels. OTEC does not discharge any CO2 and due to the deep water mixing with the upper layers of the ocean actually helps to grow phytoplankton, algae and coal which may lead to an increase on CO2 fixation.
Environmental concerns associated with OTEC systems have been brought up. One major concern is with the closed-loop and hybrid systems that depend on a low boiling point working fluid (ammonia or chlorine) to facilitate in heat exchange (Takahashi and Trenka, 1996). These potentially harmful substances could leak into the ocean if the pipes were ever damaged. Another problem would be the habitat disruption in the ocean due to the installation of the pipes (Takahashi and Trenka, 1996). Although OTEC does present potential issues that may be negative to the environment, with proper designing, research and care the negative impacts can be reduced or avoided.
5.2 ADVANTAGES.
a) OTEC uses clean, renewable, natural resources. Warm surface seawater and cold water from the ocean depths replace fossil fuels to produce electricity.
b) Suitably designed OTEC plants will produce little or no carbon dioxide or other polluting chemicals.
c) OTEC systems can produce fresh water as well as electricity. This is a significant advantage in island areas where fresh water is limited.
d) There is enough solar energy received and stored in the warm tropical ocean surface layer to provide most, if not all, of present human energy needs.
e) The use of OTEC as a source of electricity will help reduce the state's almost complete dependence on imported fossil fuels.
5.3 DISADVANTAGES:
a) OTEC-produced electricity at present would cost more than electricity generated from fossil fuels at their current costs.
b) OTEC plants must be located where a difference of about 20º C occurs year round. Ocean depths must be available fairly close to shore-based facilities for economic operation. Floating plant ships could provide more flexibility.
c) No energy company will put money in this project because it only had been tested in a very small scale.
d) Construction of OTEC plants and lying of pipes in coastal waters may cause Localized damage to reefs and near-shore marine ecosystems.
5.4 How much does an OTEC power plant cost?
The prize of the first 10-megawatt land based plant is
$40,000,000; including development costs and will produce profits of some $10,000,000 per year, which means a return of 25%. The prize of the first 100-megawatt floating plant will cost $215,000,000 and will yield profits of some $100,000,000 per year from sale of power, fresh water and seafood
6.0 Conclusion
Ocean Thermal Energy Conversion (OTEC) represents one of the most promising forms of renewable ocean energy, utilizing the natural temperature difference between warm surface seawater and cold deep seawater to generate electricity continuously. Unlike many other renewable energy sources that are dependent on weather conditions, OTEC has the advantage of providing a stable and reliable source of base-load power throughout the year in tropical and subtropical regions. This study reviewed the methodology, operating principles, classifications, applications, and performance characteristics of OTEC technology. The three major OTEC configurations—open-cycle, closed-cycle, and hybrid-cycle systems—were examined, highlighting their working mechanisms, advantages, and limitations. The analysis also identified key technical challenges affecting large-scale implementation, including low thermal efficiency, biofouling of heat exchangers, management of non-condensable gases, and the high initial capital investment required for plant construction and maintenance. Despite these challenges, OTEC offers several additional benefits beyond electricity generation. The technology can simultaneously support freshwater production through desalination, seawater air-conditioning and refrigeration, aquaculture and mariculture development, and cold-water agriculture. These integrated applications improve the overall economic viability of OTEC systems, particularly for island nations and coastal communities with limited freshwater resources and high dependence on imported fossil fuels. Although current OTEC plants operate at relatively low efficiencies of approximately 3–4%, the enormous and continuously replenished thermal energy stored in the world's oceans provides a vast and sustainable energy resource. Continued advancements in heat exchanger design, materials engineering, system optimization, and environmental management are expected to improve the commercial feasibility of OTEC technology. Therefore, with sustained research, governmental support, and industrial investment, OTEC has the potential to become an important contributor to the future global renewable energy mix and to support long-term sustainable development.
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