Report OTEC

Ocean Thermal Energy Conversion

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CHAPTER 1 INTRODUCTION

The oceans cover a little more then 70 percent of the earth surface. This makes it the world’s largest solar energy collector and energy storage system. On an average day, 60 million

square kilometers of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil. If less than one tenth of one percent of this stored solar energy could be converted into electric power, it would supply more than 20 times the total amount of electricity consumed in the United State (263 million inhabitants) on one day. The concept of OTEC (Ocean Thermal Energy Conversion) has existed for over a century as fantasized by Jules Verne in 1870 and conceptualized by French physicist, Jacques Arsene d’Arsonval, in 1881. Despite this, an operating OTEC power facility was not developed until the 1920’s.

Ocean Thermal Energy Conversion is an energy technology that converts solar radiation to electric power. OTEC utilizes the temperature difference between the warm surface seawater and deep cold sea water to produce electricity. OTEC requires a temperature difference of 36oF (20oC). This temperature difference exists between the surface and sea water year round the tropical regions of the world- within 20o of the equator in tropics. A large amount of solar energy is collected and stored in tropical oceans. The surface of the water acts as collector for solar heat, while the upper layer of the sea constitutes infinite heat storage reservoir. Thus the heat contained in the oceans could be converted into electricity by utilizing the fact that the temperature difference between the warm surface waters of the tropical oceans and colder waters in depths is about 20-25oK. Utilization of this energy with its associated temperature difference and its conversion into work forms the basis of Ocean Thermal Energy Conversion (OTEC) systems.

Dept. of EEE

College Of Engineering, Kidangoor


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2

Tropical Region

India is geographically well placed as far as the OTEC potential is concerned. Around 2000 km of coast length along the South Indian coast, a temperature difference above 20oC through out the year is available. That is 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.

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CHAPTER 2 WORKING OF 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 20oC, 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. The Basic Process

OTEC systems rely on the basic relationship between pressure (P), temperature (T) and volume (V) of a fluid, which can be expressed by the following equation: PV ÷ T = a constant where pressure, temperature and the volume of a fluid can be closely controlled by manipulating the other two variables. Hence the differential in temperature of the fluid can be used to create an increase in pressure in another. The increase in pressure is utilized to generate mechanical work.

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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 vapor expands through a turbine which is coupled to a generator that generating electric power. Cold water from the bottom is pumped through the condensers, where the vapor 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.

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CHAPTER 3 BACKGROUND AND HISTORY OF OTEC TECHNOLOGY

Attempts to develop and refine OTEC technology started in the 1880s. In 1881, Jacques Arsene d'Arsonval, a French physicist, proposed tapping the thermal energy of the ocean. D'Arsonval's student, Georges Claude, built the first OTEC plant, in Matanzas, Cuba in 1930. The system generated 22 kW of electricity with a low-pressure turbine. In 1935, Claude constructed a plant aboard a 10,000-ton cargo vessel moored off the coast of Brazil. Weather and waves destroyed it before it could generate net power. (Net power is the amount of power generated after subtracting power needed to run the system.) In 1956, French scientists designed a 3 MW plant for Abidjan, Ivory Coast. The plant was never completed, because new finds of large amounts of cheap oil made it uneconomical. In 1962, J. Hilbert Anderson and James H. Anderson, Jr. focused on increasing component efficiency. They patented their new "closed cycle" design in 1967. Japan is a major contributor to the development of the technology. Beginning in 1970 the Tokyo Electric Power Company successfully built and deployed a 100 kW closed-cycle OTEC plant on the island of Nauru. The plant became operational 1981-10-14, producing about 120 kW of electricity; 90 kW was used to power the plant and the remaining electricity was used to power a school and other places. This set a world record for power output from an OTEC system where the power was sent to a real power grid. Currently, the Institute of Ocean Energy, Saga University, is the leader and focuses on the power cycle and many of the secondary benefits. The United States became involved in 1974, establishing the Natural Energy Laboratory of Hawaii Authority at Keahole Point on the Kona coast of Hawaii. Hawaii is the best U.S. OTEC location, due to its warm surface water, access to very deep, very cold water, and Hawaii's high electricity costs. The laboratory has become a leading test facility for OTEC technology. In 1979, the first 50-kilowatt (kWe) closed-cycle OTEC demonstration plant went up at NELHA known as "Mini-OTEC," the plant was mounted on a converted U.S. Navy barge

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moored approximately 2 kilometers off Keahole Point. The plant used a cold-water pipe to produce 52 kWe of gross power and 15 kWe net power. In 1993 an open-cycle OTEC plant at Keahole Point, Hawaii, produced 50,000 watts of electricity during a net power-producing experiment. This broke the record of 40,000 watts set by a Japanese system in 1982. Lockheed Martin's Alternative Energy Development team has partnered with Makai Ocean Engineering to complete the final design phase of a 10-MW closed cycle OTEC pilot system which will become operational in Hawaii in the 2012-2013 time frame. This system is being designed to expand to 100-MW commercial systems in the near future. In November, 2010 the U.S. Naval Facilities Engineering Command (NAVFAC) awarded Lockheed Martin a US$4.4 million contract modification to develop critical system components and designs for the plant, adding to the 2009 $8.1 million contract and two Department of Energy grants totaling $1 million in 2008 and March 2010. 3.1 Indian OTEC programme

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, an OTEC cell was formed in the Indian Institute of Technology, Madras. A preliminary design was also done in 1984 for a 1 MW closed Rankine Cycle floating plant with ammonia as working fluid. After a bathymetric survey, a land based 1 MW capacity OTEC plant was suggested for one of the islands of Lakshadweep group and a detailed design report was also prepared. In 1993, National Institute of Ocean Technology (NIOT) was formed by the Department of Ocean Development (DOD), Government of India to pursue the research activities on ocean energy as part of their various mission-based activities. Under this mission a major thrust was given for the technology development for OTEC. Early 1997, DOD, Government of India proposed to establish a 1 MW gross OTEC plant in India, which will be the first ever MW range plant established anywhere in the world. NIOT had been exploring the participation of national and international expertise for a joint research and development. Saga University in Japan,

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headed by Prof. Uehara, has been doing excellent and practically oriented R & D on OTEC for more than twenty five years and this team also showed keen interest in closely working with NIOT on OTEC technology development. Considering this, an MOU was signed in 1997 between NIOT and Saga University, Japan for a joint development of OTEC in India. NIOT conducted detailed surveys at the proposed OTEC site near Tuticorin, South India. Based on the temperature and bathymetric profiles, the optimization of the closed loop systems was done with the help of Saga University in 1998. The bathymetry of the coast around main land of India where cold water at a depth of 1000 m is available at about 40 km from the shore necessitates the use of a floating platform to house the OTEC plant. There exist some locations where a shell mounted OTEC plant can be constructed at a depth of 200 m. However, considering the future need of large plants, it was decided to design a floating OTEC plant. In 2010, NIOT built a 1 MW floating OTEC plant off the coast of Tamil Nadu near Tuticorin port on the south east coast of India which is free of cyclones in the last four decades. 3.1.1 Sagar Shakthi: India's first 'power plant' on sea

Sagar Shakthi - the Ocean Thermal Energy Conversion (OTEC) Barge - a power plant, is the first of its kind in the world to generate electricity utilizing the temperature gradients between surface and deep-sea water. The barge is 68.5 m long, 16 m broad and 4 m deep, and houses the Rankine Cycle based power plant. The barge has been jointly conceived and developed by the National Institute of Ocean Technology, Chennai, and Dempo Shipbuilding and Engineering Pvt. Ltd, Goa. The principle used in OTEC barge is an innovated reverse process of refrigeration where the liquid ammonia carried at pressure in the system is vaporised in an evaporator using high temperature (28°C) surface sea water and the high energy vapour driving a sophisticated gas turbine generating electricity. The vapor ammonia, after driving the generator, is then cooled back into liquid in a condenser using deep-sea water (7°C) and routed back into the system. The process,

once

stabilized,

is

self-sustaining

and

continues

in

an

infinite

loop.

This is a technology demonstration pilot plant with provision for data collection on all aspects of the design and operation of the process, which would help developing commercial scale plants that can be deployed along the coast providing eco-friendly, renewable source of electricity. This Dept. of EEE



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pilot plant can generate 1 MW of electricity. Although some of the stages of the process have been tried out separately in laboratory and field conditions by developed countries, this is the first time an integrated full-sized plant encompassing the entire process has been built. The barge has two moon pools with warm water and cold water boxes to take in the surface and deep-sea water for the plant. The deep-sea water is taken through a 1,200 m long HDPK pipeline suspended vertically in sea by means of solid ballast and mooring buoy. The OTEC barge has one

of

the

deepest

single

point

mooring

systems

in

the

world.

The project was built by Dempo Shipbuilding and Engineering at its shipyard at Bainguinim, Goa. The OTEC barge is presently anchored 40 nautical miles off the coast of Tuticorin Port. Sagar Shakthi

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CHAPTER 4 OTEC PLANT DESIGN AND LOCATION

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. Commercial Ocean Thermal Energy Conversion (OTEC) power plants must be located in an environment that is stable enough for efficient system operation. The temperature of the warm surface sea water must differ about 20oC (36oF) from that of the cold deep water that is not more than about 1000 meters (3280 feet) below the surface. Commercial OTEC facilities can be built on

4.1



Land or Near the Shore



Platform attached to the shelf



Floating in deep ocean water 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 marine culture 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. Land based and near shore facilities offer three main advantages over those located in deep water. Plants located on or near land do not require sophisticated mooring, lengthy power cable or the more extensive maintenance associated with open ocean environments. They can be installed in sheltered areas so that they are relatively safe from storms and heavy seas. Dept. of EEE



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Electricity, desalinated water and cold, nutrient-rich sea water could be transmitted from near shore facilities via trestle bridges or causeways. In addition, land based or near shore sites allow OTEC plants to operate with related industries such as mariculture or those that require desalinated water. Favored locations include those with narrow shelves, (volcanic islands), steeps (15-20o) offshore slops and relatively smooth sea floors. These sites minimize the length of the cold water intake pipe. A land based plant could be built well inland from the shore, offering more protection from the storm, or on the beach were pipes would be shorter. In either case, easy access for construction and operation helps lower the cost of OTEC-generated electricity. Land based or near-shore sites can also support mariculture. Mariculture tanks or lagoons built on shore allow workers to monitor and control miniature marine environments. Mariculture can be delivered to market with relative ease via rail roads or highways. One disadvantage of land based facilities arises from the turbulent wave action in the surf zone. Unless the OTEC plant’s water supply and discharge pipes are buried in protective

trenches, they will subject to excessive stress during storms and prolonged periods of heavy seas. Also the mixed discharge of cold and warm sea water may need to be carried several hundred meters offshore to reach proper depth before it is released. This arrangement requires additional expense in construction and maintenance. OTEC systems can avoid some of the problems and expenses of operating in surf zone if they are built just offshore in waters ranging from 10 to 30 meters deep.(Ocean Thermal Corporation 1984). This type of plants would use shorter (and therefore less costly) intake and discharge pipes, which would avoid the dangers of turbulent surf. The plant itself would however require protection from the marine environment, such as break waters and erosion resistant foundations, and the plant output would need to be transmitted to shore. 4.2

Platform attached to the shelf

To avoid turbulent surf zone as well as to have closer access to the cold water resource, OTEC plants can be mounted to the continental shelf at depths up to 100 meters. A shelfmounted plant could be built in a shipyard, towed to the site, and fixed to the sea bottom. This type of construction is already used for offshore oil rigs. The additional problems of operating an OTEC plant in deeper water, however, may make shelf mounted facilities less desirable and more expensive than their land based counter part. Problems with shelf mounted parts include the stress of open-ocean conditions and more difficult product delivery. Having to consider Dept. of EEE



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strong ocean currents and large waves necessitates additional engineering and construction expense. Platforms require extensive piling to maintain a stable base for OTEC operation. Power delivery could also become costly because of the long underwater cables required to reach land. For these reasons, shelf-mounted plants are less attractive for near term development. 4.3

Floating Power plant

The floating power plant works in the same way as the land based the apparent difference is that the floating plant is floating. A floating plant can have a vertical cold water pipe, which only need to be1000 meters. The fundamental reason why a land based plant costs 3 times as much per unit power output, as a sea-based plant is the expense of the cold water pipe. Floating OTEC facilities could be designed to operate off-shore. Although potentially preferred for systems with large power capacity, floating facilities present several difficulties. This type of plant is more difficult to stabilize, an d the difficulty of mooring it in very deep water may create problems with power delivery. Cables attached to floating platforms are more susceptible to damage, especially during storms. Cables at depths greater than 1000 meters are difficult to maintain and repair. Riser cables, which span the distance between the sea bed and the plant, need to be constructed to resist entanglement. As with shelf-mounted plants, floating plants need a stable base for continuous OTEC operation. Major storms and heavy seas can break the vertically suspended cold water pipe and interrupt the intake of warm water as well. To help prevent these problems, pipes can be made of relatively flexible polyethylene attached to the bottom of the platform and gimbaled with joints or collars. Pipes may need to be uncoupled from the plant to prevent damage during storms. As an alternative to having a warm water pipe, surface water can be drawn directly into the platform; however it is necessary to locate the intake carefully to prevent the intake flow from being interrupted during heavy seas when the platform would heave up and down violently. If a floating plant is to be connected to power delivery cable, it needs to remain relatively stationary. Mooring is an acceptable method, but current mooring technology is limited to depths of about 2000meters (6560 feet). Even at shallower depths, the cost of mooring may prohibit commercial OTEC ventures. An alternative to deep water OTEC may be drifting or self propelled plant ships. These ships use their net power to manufacture energy intensive products such as hydrogen, methanol or ammonia. Electricity generated by plants fixed in one place can

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be delivered directly to a utility grid. A submersed cable would be required to transmit electricity from an anchored floating platform to land.

Fig.1 General View of OTEC Plant

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Fig.2 Operating head of OTEC Plant

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Fig.3 OTEC Power Plant

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CHAPTER 5 OTEC SYSTEMS

There are basically three types of OTEC systems developed that can utilize sea water temperature differentials – they are: a closed-cycle, an open-cycle and a hybrid-cycle. 5.1

Closed-Cycle

The closed-cycle system uses a low boiling point working fluid, such as ammonia, pumped around a closed loop, which has three components: a pump, turbine and heat exchanger (evaporator and condenser). The heat from warm seawater flowing through an evaporator vaporizes the working fluid. The vapor expands through a turbine, and then flows into a condenser where cold seawater condenses it into a liquid. Early 1997, DOD, Government of India proposed to establish a 1 MW gross OTEC plant in India, which will be the first ever MW range plant established anywhere in the world. NIOT had been exploring the participation of national and international expertise for a joint research and development. Saga University in Japan, headed by Prof. Uehara, has been doing excellent and practically oriented R & D on OTEC for more than twenty five years and this team also showed keen interest in closely working with NIOT on OTEC technology development. Considering this, an MOU was signed in 1997 between NIOT and Saga University, Japan for a joint development of OTEC in India. NIOT conducted detailed surveys at the proposed OTEC

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site near Tuticorin, South India. Based on the temperature and bathymetric profiles, the optimization of the closed loop systems was done with the help of Saga University in 1998. The bathymetry of the coast around main land of India where cold water at a depth of 1000 m is available at about 40 km from the shore necessitates the use of a floating platform to house the OTEC plant. There exist some locations where a shell mounted OTEC plant can be constructed at a depth of 200 m. However, considering the future need of large plants, it was decided to design a floating OTEC plant. NIOT built a 1 MW floating OTEC plant off the coast of Tamil Nadu near Tuticorin port on the south east coast of India which is free of c yclones in the last four decades. POWER MODULE AND SEA WATER SYSTEMS

All commercial OTEC plants are expected to be 10 - 50 MW range or larger. Therefore a 1 MW gross power output plant is selected for the present design, considering the scaling up for the future. The design of the power module is based on a closed Rankine Cycle with ammonia as the working fluid. Titanium plate heat exchangers are suitable to such an environment. A cold water pipe made of HDPE of 1m outer diameter is selected, as it is the largest diameter locally available. Axial flow turbine having a higher adiabatic efficiency is chosen for power conversion and also for easy scaling up for future. The following are the baseline design conditions. Gross Power Output 1MW Warm Water Temperature 29 o C Cold water temperature 7o C Cold water intake 1000 m Cold water pipe (ID) 0.90

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Open Cycle

The open-cycle system is generally similar to the closed-cycle system and uses the same basic components. The open-cycle system uses the warm seawater as the working fluid. The warm seawater passing through the 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 desalinized water. The desalinated water is pure fresh water for domestic and commercial use. (The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid).

5.3

Hybrid Cycle

The hybrid system uses parts of both open-c ycle and closed-cycle systems to produce electricity and desalinated water. In this arrangement, electricity is generated in the closed cycle system and the warm and cold seawater discharges are passed through the flash evaporator and condenser of the open-cycle system.

5.4

Working fluids

A popular choice of working fluid is ammonia, which has superior transport properties, easy availability, and low cost. Ammonia, however, is toxic and flammable. Fluorinated carbons such as CFCs and HCFCs are not toxic or flammable, but they contribute to ozone layer depletion. Hydrocarbons too are good candidates, but they are highly flammable; in addition, this Dept. of EEE



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would create competition for use of them directly as fuels. The power plant size is dependent upon the vapor pressure of the working fluid. With increasing vapor pressure, the size of the turbine and heat exchangers decreases while the wall thickness of the pipe and heat exchangers increase to endure high pressure especially on the evaporator side.

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CHAPTER 6 EFFICIENCY OF OTEC POWERPLANT

Theoretically, it is possible to convert the energy in a 23-temperature difference at an efficiency of 7-8%. Early OTEC systems were of 1 to 3% thermal efficiency, well below the theoretical maximum for this temperature difference. Current designs are exp ected to be closer to the maximum. The first operational system was built in Cuba in 1930 and generated 22 kW. Modern designs allow performance approaching the theoretical maximum Carnot efficiency and the largest built in 1999 by the USA generated 250 kW. This energy is equivalent to the same amount of water passing through a h ydroelectric 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 b y 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%. To count this efficiency you can use an equation, which is called the Carnot factor, and can be presented like this:

 

=w

Where T1- Temp at surface level T2- Temp at bottom level W- Work And if you use the values, surface temperature 27C and deep temperature 4C, the equation looks like this:  

=0.076=7.6%

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CHAPTER 7 APPLICATIONS OF OTEC

OTEC Applications besides producing electricity 

Air Conditioning

The cold water can be used as a fluid in air condition systems because the temperature is only a few degrees. It can chill fresh water in a heat exchanger or flow directly into the cooling system. 

Chilled Soil Agriculture

OTEC Technology also supports chilled soil agriculture. When cold sea water flows through underground pipes, it chills the surrounding soil. The temperature difference between plant roots in the cold soil and plant leaves in the warm air allows many plants that evolved in temperate climates to be grown in subtropics.

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Aquaculture

Aquaculture is perhaps the most well known byproduct of OTEC. Cold water delicacies such as salmon and lobster thrive in the nutrient rich, deep, sea water from the OTEC process. Microalgae such as Spirulina, a health food supplement, also can be cultivated in the deep ocean water. 

Desalination

Desalination, the production of fresh water from sea water, is another advantage of open or hybrid cycle OTEC plants. Theoretically an OTEC plant that generates 2MW of net electricity could produce about 4300 cubic meters of desalinated water each day. This is equivalent to 4.3 million litres. 

Mineral Extraction

OTEC may one day provide a means to mine ocean water for 57 trace elements. Most economic analyses have suggested that mining the ocean for dissolved substances would be unprofitable because so much energy is required to pump the large volume of water needed and because of the expense involved in separating the minerals from seawater. But with OTEC plants already pumping the water, the only remaining economic challenge is to reduce the cost of extraction process.

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CHAPTER 8 ADVANTAGES & DISADVANTAGES Advantages 1. OTEC uses clean, renewable, natural resources. Warm surface seawater and cold water from

the ocean depths replace fossil fuels to produce electricity. 2. Suitably designed OTEC plants will produce little or no carbon dioxide or other polluting

chemicals. 3. OTEC systems can produce fresh water as well as electricity. This is a significant advantage in

island areas where fresh water is limited. 4. 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. 5. OTEC helps in mining ocean water for 57 trace elements. Most economic analyses have

suggested that mining the ocean for trace elements would be unprofitable as so much energy is required to pump the large volume of water needed and because of the expense involved in separating the minerals from seawater. But in OTEC plants already pumping the water, the only remaining economic challenge is to minimize the cost of the extraction process.

Disadvantages 1. OTEC-produced electricity at present would cost more than electricity generated from fossil

fuels at their current costs. 2. 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. 3. Construction of OTEC plants and lying of pipes in coastal waters may cause localized damage

to reefs and near-shore marine ecosystems.

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CHAPTER 9 FUTURE OF OTEC 9.1 Current Issues and Future Plans

It is postulated that most of the future commercial OTEC plants are closed -cycle, floating plants of 10-50 MW range. But plants of 200-400 MW range are also feasible and economically more attractive. The commercial plants should be preceded by demonstration plants of smaller range for power cycle optimization and also for operational information. The design, development and operation of a power system in a hostile sea environment is a great challenge. The capital cost of the plant is depending much on the heat exchanger cost and hence any improvement in the performance in this single component is an added advantage. Attempts are to be done to find out a proven technology for heat exchangers in seawater conditions with higher heat transfer co-efficient for considerable period of time. The design, fabrication and deployment of seawater system in the environment of the sea is a matter of considerable attention. New materials for the cold water pipe is to be developed to withstand the marine conditions and also for easy fabrication and deployment. The design of the barge also requires care so as to position the seawater pumps for the required Net Positive Suction Head (NPSH). The equipment and the piping system are to be assembled on the barge such a way that the static head and the minor losses are the least. Bio fouling on the warm water circuit and the release of the dissolved gasses in the cold water circuit is a problem to be attended for a considerably long period. As the floating plants are away from seashore underwater po wer transmission to the land is an area needed further study. 9.2 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 an d will yield profits of some $100,000,000 per year from sale of power, fresh water and seafood As you can see the power plant will make profit within a period of 5 years.

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To get more prizes or details about the different parts of incomes visit the WebPages: www.seasolarpower.com 9.3 Environment

One of the most critical problems of the next century will certainly be global warming. OTEC is unique among all energy generation the technologies in that not only does it generate no carbon dioxide whatsoever, but it actually counteracts the effects of fossil fuel use. OTEC involves bringing up mineral-rich water from the depths of the oceans. This water will promote growth of photosynthetic phytoplankton. These organisms will absorb carbon dioxide from the atmosphere into their bodies, and when they die, or when the animals, which eat them, die, the carbon dioxide will be sequestered in the depths of the oceans. The effect is not small. Each 100megawatt OTEC plant will cause the absorption of an amount of carbon dioxide equivalent to that produce by fossil fuel power plant of roughly the same capacity. No other energy technology ever imagined can do this. OTEC plants construction, with laying pipes in coastal waters ma y cause localized damage to reefs and near-shore marine ecosystems.

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CHAPTER 10 CONCLUSION

Using the temperature difference in the oceans is not a new idea. People have been talked about this for over hundred years. This piece is written by Jules Verne, from the book ”Twenty Thousands Leagues under the Sea”. I was determined to seek from the sea alone the means of producing my electricity. From the sea? Yes, Professor, and I was at no loss to find these means. It would have been possible, by establishing a circuit between two wires plunged to different depths, to obtain electricity by the difference of temperature to which they would have been exposed...

The fossil fuels will in the near future be consumed, so we had to find some alternative energy sources. OTEC is a source, which uses the renewable solar collector the sea, instead o f an artificial collector. This can in the future be an alternative to the nuclear power and the fossil fuels. The problem is that this invention will be more expensive than the fossil fuels power plants, and it will take a long time before anyone will put some money in this project and outrival the now existing plants. But as long as the sun heats the waters of the oceans, the potential for power conversion though OTEC will always exist. Now there is a considerable interest in different parts of the world thou gh there was sluggishness in OTEC research during 1985-1995 periods due to the fall in oil prices. The key problem is now no longer technological or commercial, but the establishment of reliability and confidence. There is an absolute necessity to build demonstration plants representing the nature of future commercial plants. The demonstration of 1 MW Indian OTEC program is expected to contribute in a large way to provide this confidence to the future.

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REFERENCES 

Solar Engineering

-

H P Gupta



Solar Thermal Engineering

-

Duffie and Dackuran



Renewable Energy Sources

-

G D Rai



Solar Thermal Engineering System -



Uehara. H, and Ikegami Y, ¡§Optimization of a closed cycle OTEC system¡¨, ASME

G N Tiwari

Journal of Solar Energy Engineering, Vol. 112, No.4, pp. 247 ¡V 256 (1990) 

R. Abraham et al, ¡§Analysis of Power Cycle for 1 MW Floating OTEC plant¡¨, Accepted paper for IOA ¡¦99 Conference IMARI (1999)



P. Jalihal et al, ¡§Analysis of Integrated CWP / Barge System for 1 MW OTEC plant¡¨, Accepted paper for IOA ¡¦99 Conference, IMARI (1999)



Avery, W. H. and Wu, Renewable Energy from the Ocean ¡V a guide to OTEC¡¨, Oxford University Press, pp. 280 (1994)



Luis A. Vega and Donald E. Evans ¡§Operation of a Small Open Cycle OTEC experimental facility¡¨, Renewable Energy Technologies, pp. 93 ¡V 117 (1992)



Luis A. Vega, ¡§Economics of Ocean Thermal Energy Conversion¡¨, Ocean Energy Recovery, pp. 152-181 (1992)



George Hagerman, ¡§Wave Power Economics¡¨, Ocean Energy Recovery, pp. 152-181 (1992)



Lennard. D.E, ¡§Ocean Thermal Energy Conversion, ¡§ IOA News Letter Vol. 10, No.2 / Summer, pp.3(1999)

WEB REFERENCE: 

http://www.exergy.se/ftp/aes.pdf



http://www.seasolarpower.com



http://rclsgi.eng.ohio-state.edu/~kerechan/OTEC2.html



http://www.nrel.gov/otec/what.html



http://www.trellis.demon.co.uk/reports/otec_sites.html



http://www.sprl.umich.edu/PHAYS/Chap_6/Chap_6_GIFS



http://starfire.ne.uiuc.edu/~ne201/1995/wantland/otec.html



http://wsi-www1.cso.uiuc.edu/courses/GEOL105a/MODULES/



lectures/resources/lect838737281.html

Dept. of EEE



28



http://hgea01.hgea.org/~daver/otecengy.htm



[email protected]



http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion



http://www.otecnews.org/



http://images.google.co.in/images?hl=en&source=hp&q=OTEC&gbv=2&aq=f&oq=



http://www.clubdesargonautes.org/otec/vol/vol11-2-1.htm



http://www.everestblowers.com/technical-articles/lttd_2.pdf

Dept. of EEE


Report OTEC

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