Ocean thermal energy conversion
In the past century, it has been seen that the consumption of non-renewable sources of energy has caused more environmental damage than any other human activity. Electricity generated from fossil fuels such as coal and oil has led to high concentrations of harmful gases in the atmosphere. This has in turn led to many problems being faced today such as global warming.
Therefore, alternative sources of energy have become very important and relevant to today's world. For that fact, I´m talk about Ocean Thermal Energy Conversion because it´s a very new and unknown technology.
And I´d like to answer the four following questions:
. What is Ocean Thermal Energy Conversion?
. Where is it possible to build an OTEC power plant?
. How does it work?
. Is there a market for OTEC plants?
So what's Ocean Thermal Energy Conversion?
The oceans cover a little more than 70 percent of the Earth's surface.
This makes them 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 States on any given day.
OTEC, or ocean thermal energy conversion, is an energy technology that converts solar radiation to electric power. As long as the temperature between the warm surface water and the cold water in a depth of one kilometer or even deeper differs by about 20°C, an OTEC system can produce a significant amount of power. This conditions have been found between latitudes 20 deg N and 20 deg S.
Within this tropical zone are portions of two industrial nations-the United States and Australia-and 66 developing nations. Of all these possible sites, tropical islands with growing power requirements and a dependence on expensive imported oil are the most likely areas for OTEC development.
At the time there are actually two systems of OTEC plants the closed cycle system and the open cycle system.
Closed-Cycle OTEC System
As you can see warm seawater is getting pumped through a evaporator (it´s also called a heat exchanger) there it vaporizes a working fluid, such as ammonia with a boiling point of 10-15°, then the water gets back in the sea. The vapor of the working fluid drives a turbine coupled to a generator that produces electricity. Then the vapor gets to the condenser it´s another heat exchanger but it´s using cold seawater pumped from the deep ocean to condens the working fluid.
In the end the condensed working fluid is pumped back to the evaporator to repeat the cycle.
Open-Cycle OTEC System
In an open-cycle OTEC system, the warm seawater is the working fluid. The warm seawater is evaporated in a vacuum chamber to produce steam at an absolute pressure of about 2.4 kilopascals (kPa). The steam expands through a low-pressure turbine that is coupled to a generator to produce electricity. The steam exiting the turbine is condensed by cold seawater pumped from the ocean's depths through a cold-water pipe.
As you can see the open system is nealy the same than the closed system but with one big advantage. The condensed sea water can be used as drinking water. System analysis indicates that a 2-megawatt plant could produce about 4300 cubic meters of desalinated water each day.
But as you can imagine it isn´t very easy to operate a OTEC plant because of the high energy demand for pumping the water or the vacuum. For that fact the biggest OTEC test-plant, it was built in May 1993, at Keahole Point, Hawaii, produced just 50 kilo watts of electricity during a net power-producing experiment. But there have also been plans for bigger OTEC plants in 1956, French researchers designed a 3-megawatt open-cycle plant for Abidjan on Africa's west coast.
But the plant was never completed because of competition with inexpensive hydroelectric power.
Infact a 3 megawatt power plant isn't very much if you complain it to a modern nuclear power staion with more than 1000 mega watts.
For that reason OTEC systems are nowadays just a good option for small islands with a little demand of energy.
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