ADVERTISEMENTS:
Here is a compilation of essays on ‘Ocean Thermal Energy’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Ocean Thermal Energy’ especially written for school and college students.
Essay on Ocean Thermal Energy
Essay Contents:
- Essay on the Introduction to Ocean Thermal Energy
- Essay on the Conversion of Ocean Thermal Energy
- Essay on the History of Ocean Thermal Energy
- Essay on the Types of OTEC Plants
- Essay on the Applications of Ocean Thermal Energy
- Essay on the Technical Difficulties Encountered in OTEC Plants
ADVERTISEMENTS:
ADVERTISEMENTS:
Essay # 1. Introduction to Ocean Thermal Energy:
The ocean can produce two types of energy thermal energy from the sun’s heat and mechanical energy from the tides and waves. Oceans cover more than 70% of Earth’s surface, making them the world’s largest solar collectors. The sun’s heat warms the surface water a lot more than the deep ocean water, and this temperature difference creates thermal energy. Just a small portion of the heat trapped in the ocean could power the world.
The energy from the sun heats the surface water of the ocean. In tropical regions, the surface water can be 40 or more degree warmer than the deep water. This temperature difference can be used to produce electricity. Ocean Thermal Energy Conversion (OTEC) has the potential to produce more energy than tidal, wave and wind energy combined.
The OTEC systems can be open or closed. In a closed system, an evaporator turns warm surface water into steam under pressure. This steam spins a turbine generator to produce electricity. Water pumps bring cold deep water through pipes to a condenser on the surface.
ADVERTISEMENTS:
The cold water condenses the steam and the closed cycle begins again. In an open system, the steam is turned into fresh water and new surface water is added to the system. A transmission cable carries the electricity to the shore.
The OTEC systems must have a temperature difference of about 25 degrees Celsius to operate. This limits OTEC’s use to tropical regions where the surface waters are very warm and there is deep cold water. Hawaii, with its tropical climate, has experimented with OTEC systems since the 1970’s.
ADVERTISEMENTS:
Today, there are several experimental OTEC plants, but no large operations. There are many challenges to widespread use. The OTEC systems are not very energy efficient. Pumping the water is a giant engineering challenge. In addition, the electricity must be transported to land. It will probably be 10 to 20 years before the technology is available to produce and transmit electricity economically from OTEC systems.
Essay # 2. Conversion of Ocean Thermal Energy:
Ocean thermal energy conversion (OTEC or OTE) uses the temperature difference that exists between deep and shallow waters to run a heat engine. As with any heat engine, the greatest efficiency and power is produced with the largest temperature difference. This temperature difference generally increases with decreasing latitude, i.e., near the equator, in the tropics.
Historically, the main technical challenge of OTEC was to generate significant amounts of power efficiently from this very small temperature ratio. Changes in efficiency of heat exchange in modern designs allow performance approaching the theoretical maximum efficiency.
The Earth’s oceans are continually heated by the sun and cover over 70% of the Earth’s surface; this temperature difference can potentially be harnessed as a renewable energy resource with a total available energy of one or two orders of magnitude higher than other ocean energy options such as wave power; but the small magnitude of the temperature difference makes energy extraction comparatively difficult and expensive, due to low thermal efficiency.
Earlier OTEC systems had an overall efficiency of only 1 to 3% (the theoretical maximum efficiency lies between 6 and 7%). Current designs under review will operate closer to the theoretical maximum efficiency.
The energy carrier, seawater, is free, though it has an access cost associated with the pumping materials and pump energy costs. Although an OTEC plant operates at a low overall efficiency, it can be configured to operate continuously as a Base load power generation system.
The concept of a heat engine is very common in thermodynamics engineering, and much of the energy used by humans passes through a heat engine. A heat engine is a thermodynamic device placed between a high temperature reservoir and a low temperature reservoir. As heat flows from one to the other, the engine converts some of the heat energy to work energy.
ADVERTISEMENTS:
This principle is used in steam turbines and internal combustion engines, while refrigerators reverse the direction of flow of both the heat and work energy. Rather than using heat energy from the burning of fuel, OTEC power draws on temperature differences caused by the sun’s warming of the ocean surface.
The only heat cycle suitable for OTEC is the Rankine cycle using a low-pressure turbine. Systems may be either closed-cycle or open-cycle. Closed-cycle engines use working fluids that are typically thought of as refrigerants such as ammonia or R-134a. Open-cycle engines use the water heat source as the working fluid.
Essay # 3. History of Ocean Thermal Energy:
There have been many periodic attempts to develop and refine OTEC technology starting in the 1800s. In 1881, Jacques Arsene d’Arsonval, a French physicist, proposed tapping the thermal energy of the ocean. It was d’Arsonval’s student, Georges Claude who actually built the first OTEC plant, in Cuba in 1930. The system generated 22 kW of electricity with a low-pressure turbine.
In 1931, Nikola Tesla released “Our Future Motive Power” which covered an ocean thermal energy conversion system. Although initially excited about the idea. Tesla ultimately came to the conclusion that the scale of engineering required for the project made it impractical for large scale development.
In 1935, Claude constructed another plant, this time aboard a 10,000-ton cargo vessel moored off the coast of Brazil. Weather and waves destroyed both plants before they could become net power generators. (Net power is the amount of power generated after subtracting power needed to run the system.)
In 1956, French scientists designed a 3MW plant for Abidjan, Ivory Coast. The plant was never completed, however, because large amounts of cheap oil became available in the 1950s making oil fired power plants more economical.
The United States became involved in OTEC research in 1974, when the Natural Energy Laboratory of Hawaii Authority was established at Keahole Point on the Kona coast of Hawaii. The laboratory has become one of the world’s leading test facilities for OTEC technology. Hawaii is often said to be the best location in the US for OTEC, due to the warm surface water, excellent access to very deep, very cold water, and because Hawaii has the highest electricity costs in the US.
Although Japan has no potential OTEC sites it has been a major contributor to the development of the technology, primarily for export to other countries. 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, which became operational in 1981, produced about 120 kW of electricity; 90 kW was used to power the plant itself and the remaining electricity was used to power a school and several other places in Nauru. This set a world record for power output from an OTEC system where the power was sent to a real power grid.
India piloted a 1-MW floating OTEC plant near Tamil Nadu. Its government continues to sponsor various research in developing floating OTEC facilities.
Essay # 4. Types of OTEC Plants:
OTEC Plants can be classified on the basis of:
(i) Location.
(ii) Cycle.
(i) Depending on the Location:
a. Land Based Plant:
Land-based and near-shore facilities offer three main advantages over those located in deep water. Plants constructed on or near land do not require sophisticated mooring, lengthy power cables, 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.
Electricity, desalinated water, and cold, nutrient-rich seawater 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), steep (15-20 deg) offshore slopes, 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 storms, or on the beach, where the 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 products can be delivered to market with relative ease via railroads 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 be subject to extreme stress during storms and prolonged periods of heavy seas.
Also, the mixed discharge of cold and warm seawater may need to be carried several hundred meters offshore to reach the 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 a surf zone if they are built just offshore in waters ranging from 10 to 30 meters deep (Ocean Thermal Corporation 1984). This type of plant would use shorter (and therefore less costly) intake and discharge pipes, which would avoid the dangers of turbulent surf. The plant itself, however, would require protection from the marine environment, such as breakwaters and erosion-resistant foundations, and the plant output would need to be transmitted to shore.
b. Shelf Based Plant:
To avoid the 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 shelf-mounted 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 counterparts. Problems with shelf-mounted plants include the stress of open-ocean conditions and more difficult product delivery.
Having to consider strong ocean currents and large waves necessitates additional engineering and construction expense. Platforms require extensive pilings 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 OTEC development.
c. Floating Plant:
Floating OTEC facilities could be designed to operate off-shore. Although potentially preferred for systems with a large power capacity, floating facilities present several difficulties. This type of plant is more difficult to stabilize, and 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 gimballed 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 cables, it needs to remain relatively stationary. Mooring is an acceptable method, but current mooring technology is limited to depths of about 2000 meters (6560 feet). Even at shallower depths, the cost of mooring may prohibit commercial OTEC ventures.
(ii) Depending on the Cycle used:
a. Open cycle.
b. Closed cycle.
c. Hybrid cycle.
This cold seawater is an integral part of each of the three types of OTEC systems-closed-cycle, open-cycle, and hybrid. To operate, the cold seawater must be brought to the surface. This can be accomplished through direct pumping. A second method is to desalinate the seawater near the sea floor; this lowers its density, which will cause it to ‘float’ up through a pipe to the surface.
The alternative to costly and massive, cold water pipes bring condensing cold water to the surface is to pump the much smaller volume of vaporized low boiling point fluid into the depths to be condensed thus overcoming a massive technical and environmental problem and lowering the cost of OTEC.
a. Open-Cycle:
Open-cycle OTEC uses the tropical oceans’ warm surface water to make electricity. When warm seawater is placed in a low-pressure container, it boils. The expanding steam drives a low-pressure turbine attached to an electrical generator.
The steam, which has left its salt and contaminants behind in the low-pressure container, is pure fresh water. It is condensed back into a liquid by exposure to cold temperatures from deep-ocean water. This method has the advantage of producing desalinized fresh water, suitable for drinking water or irrigation.
b. Closed-Cycle:
Closed-cycle systems use fluid with a low boiling point, such as ammonia, to rotate a turbine to generate electricity. Warm surface seawater is pumped through a heat exchanger where the low-boiling-point fluid is vaporized. The expanding vapor turns the turbo-generator. Then, cold, deep water—pumped through a second heat exchanger—condenses the vapor back into a liquid, which is then recycled through the system.
c. Hybrid:
A hybrid cycle combines the features of both the closed-cycle and open-cycle systems. In a hybrid OTEC system, warm seawater enters a vacuum chamber where it is flash-evaporated into steam, similar to the open-cycle evaporation process.
The steam vaporizes the ammonia working fluid of a closed-cycle loop on the other side of an ammonia vaporizer. The vaporized fluid then drives a turbine to produce electricity. The steam condenses within the heat exchanger and provides desalinated water.
The electricity produced by the system can be delivered to a utility grid or used to manufacture methanol, hydrogen, refined metals, ammonia, and similar products.
Essay # 5. Applications of Ocean Thermal Energy:
OTEC has important benefits also other than power production.
These are:
(i) Air Conditioning:
The 41°F (5°C) cold 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 cold seawater from an OTEC plant can be used in chilled-water coils to provide air-conditioning for buildings.
(ii) Chilled-Soil Agriculture:
OTEC technology also supports chilled-soil agriculture. When cold seawater flows through underground pipes, it chills the surrounding soil. The temperature difference between plant roots in the cool soil and plant leaves in the warm air allows many plants that evolved in temperate climates to be grown in the subtropics.
(iii) Aquaculture:
Aquaculture is the most well-known by-product of OTEC. It is widely considered to be one of the most important ways to reduce the financial and energy costs of pumping large volumes of water from the deep ocean.
Deep ocean water contains high concentrations of essential nutrients that are depleted in surface waters due to biological consumption. This ‘artificial upwelling’ mimics the natural upwelling that are responsible for fertilizing and supporting the world’s largest marine ecosystems, and the largest densities of life on the planet.
(iv) Desalination:
Desalinated water can be produced in open- or hybrid-cycle plants using surface condensers. In a surface condenser, the spent steam is condensed by indirect contact with the cold seawater. This condensate is relatively free of impurities and can be collected and dispensed to local communities where supplies of natural freshwater for agriculture or drinking are limited.
Essay # 6. Technical Difficulties Encountered in OTEC Plants:
There are certain technical difficulties which are encountered in OTEC plants.
These are:
i. Degradation of heat exchanger performance by dissolved gases.
ii. Degradation of heat exchanger performance by microbial fouling.
iii. Improper sealing.
The evaporator, turbine, and condenser operate in partial vacuum ranging from 3% to 1% atmospheric pressure. This poses a number of practical concerns. First, the system must be carefully sealed to prevent in-leakage of atmospheric air that can severely degrade or shut down operation.