Introduction: The population of the world continues to grow. Now, more than ever before, alternative energies have become an economic, social, and environmental necessity. The huge demand for energy, and especially Renewable Energy, around the world push us to seek new sources of energy. Generating renewable energy from the ocean through Ocean Thermal Energy Conversion, known as O.T.E.C. is one of the sources; it has been studied for nearly a century but, although several demonstration plants have been built to prove that the technology works, it has never been put into commercial operation. Now, however, despite the high costs involved, several companies are working toward commercial projects.
Overview:
OTEC is a marine renewable energy technology that is using the solar energy absorbed by the oceans in form of heat. OTEC generates electricity by exchanging heat with the warm water from the ocean surface and with the cold water from the deep ocean.
History:
The science behind ocean thermal energy conversion was first explored in France in the late 19th century and an experimental O.T.E.C. plant was built and briefly operated by a French engineer, Georges Claude, in Cuba in 1930. In the 1970s, as the first oil crisis hit, several countries started to look more seriously at the technology. In the 1980s however, as oil prices slid back, attention shifted away. [Source: Google]
Two types of OTEC:
Closed Cycle OTEC (CC-OTEC)
Surface water is pumped through a heat exchanger, where it heats a fluid with a very low boiling point, such as ammonia, which expands as it vaporizes. The vaporized gas drives turbines producing electricity before being piped into a condenser, where cold deep ocean water chills it, returning it to its liquid state. The liquid is then pumped back to the warm water heat exchanger to repeat the cycle.

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(Source: Google)

Open Cycle OTEC (CC-OTEC)
OC-OTEC systems are defined by their utilization of the warm surface water as the working fluid. Therefore, the system is “Open” because the ocean water is not completely separated from the turbine. The efficiency of an OC-OTEC is higher because a larger portion of the temperature difference is available to produce power. In addition, it can also be used to provide drinking water.

[pic]

(Source: Google)

Efficiency:
OTEC is not so efficient, according to the laws of physics that says any practical heat engine must operate at less than 100% efficiency.

Efficiency = (Energy out / Energy in) x 100%

[Source: Thermodynamics, Chapter IV. Heat engines and efficiency]

OTEC have among the lowest efficiency of all. For that reason, OTEC plants have to work very hard to increase it`s working efficiency.
Overall:
OTEC is clean, green renewable energy, it doesn’t produce large amounts of greenhouse gases, or releasing toxic air pollution, but it carries its advantages and disadvantages in economic and environmental aspects.

Advantages:
An important advantage of this method of producing energy is that it could run all the time, unlike solar plants, which cannot work at night, or wind turbines, which stop in calm conditions.
OTEC can play a useful part in providing pure, usable water from ocean water.
OTEC can also be used to produce fuels such as hydrogen.
The waste cooling water used by an OTEC plant can also be used for aquaculture, refrigeration, and air conditioning.
Disadvantages:
First is it`s need of huge amount of the electricity that have to be used for operating the system.
Second is the need of a land, with relatively large scale, to be built on, which makes them expensive investments. Large-scale onshore OTEC plants will have an environmental impact on shorelines threatening ecosystems such as mangroves and coral reefs.
This technology is expensive and can work in only a limited number of places, like the tropics, where there is a large difference in temperature between the ocean’s layers, and also places with very deep waters near to the shore line.

Impacts:
Although OTEC technology is not new, a commercial power plant has yet to be built. Still, however, the technology does have the ability to tap into a large source of stored solar energy. Before throwing out (or accepting!) the further development and implementation of OTEC, one should consider the barriers to commercialization, the environmental impact of its implementation.
Economical;
When deciding whether to approve the implementation or development of an OTEC, one factor that we should consider is the economic feasibility of the process. While considering the economic feasibility of any commodity is under scrutiny, we must consider more than the total cost of the production of the commodity: we must also consider the feasibility of substitutes for the commodity. We must also bear in mind that the main function of OTEC technology is a power plant. While co-products such as water and aquaculture products can add to the revenue generated by the facility itself, the end purpose is to replace power produced by oil with power produced by a cleaner renewable source. The first barrier to overcome in terms of economic feasibility was the production of a net power output. However, a net power production at a high cost per unit energy relative to other energy sources is not economically feasible. Research since then has produced cycle developments in the cycles themselves and the materials used in developing the equipment. [Source: Report based on OTEC build in Hawaii in 1979]

Environmental;
This technology would not leave its surroundings unscathed. - A huge amount of cold water would have to be pumped up from the depths. If that water, which is rich in nutrients, is discharged into a different part of the ocean, it could confuse fish and alter the balance of the ecosystem. - The warm water must be siphoned in slowly enough so that fish could swim away. - Temperature changes leading to environmental impact. The extensive effect of this may cause unknown long term effects. The injection of cold water about 3.5˚ C above the local temperature will change salinity, nutrient distribution, mixed layer depths and sea-surface temperatures, among other things. - Effect on small marine life passed through the system would certainly be a concern. Although filters would be used, the system would definitely not filter all marine life or prevent damage to marine life that does not have sufficient mobility. - Pollution, Chlorine input when using ammonia. - In the case of sea solar power, the working fluid is propylene. Ammonia isn’t as bad as propylene environmentally, but propylene is apparently more cost effective. - Direct impact upon marine life passed through an OTEC.

Social;
We also need to consider the social impact of building an OTEC on shore or nearby. People will not easily accept that a huge Power plant will be build nearby their homes, bringing its pollution during construction, noise and most important – building it with their money (government).

Conclusion:
Ocean thermal energy conversion is a potential source of renewable energy that creates no emissions. The main advantages of OTEC is that the method is fuel free, has a low environmental impact, can supply pure water for both drinking and agriculture, can supply refrigeration and cooling and can provide a coastal community with reliable energy. The disadvantages, economically, environmentally and socially impacts.

Overall, the OTEC technology is continuing to be developed, and maybe someday it will give us its full potential.