Como trabaja el otec:

Carnot Efficiency : In transferring heat to do work, the greater the spread in temperature between the heat source and the heat sink, the greater the efficiency of the energy conversion. As long as the temperature between the warm surface water and the cold deep water differs by about 20°C (36°F), an OTEC system can produce a significant amount of power with a maximum Carnot Efficiency of about 6.7%

Hsitoria

In 1881 jackes arsene a french physicist has proposed tapping thermal energy from ocean.  His idea called for a closed-cycle system, a design that has been adapted for most present-day OTEC pilot plants. Such a system employs a secondary working fluid (a refrigerant) such as ammonia.   Heat transferred from the warm surface ocean water causes the working fluid to vaporize through a heat exchanger. The vapour then expands under moderate pressures, turning a turbineconnected to a generator and thereby producing electricity. Cold seawater pumped up from the ocean depths to a second heat exchanger provides a surface cool enough to cause the vapour to condense. The working fluid remains within the closed system, vaporizing and reliquefying continuously.

• In the year 1930 his student named George Claude built otec plant in Matanzas, Cuba which generated 22kw of power.

• 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.

• Today, scientists are developing new, cost-effective, state-of-the-art turbines for open-cycle OTEC systems, experimenting with anti corroding Titanium and plastics as rotor material.

• The new designs for OTEC are still mostly experimental. Only small-scale versions have been made. The largest so far is near Japan, and it can create 100 kilowatts of electricity.

Open cicle:

• 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 behind in the low-pressure container, is almost pure fresh water. It is condensed back into a liquid by exposure to cold temperatures from deep-ocean water.

• Closed-cycle systems use fluid with a low-boiling point, such as ammonia, to rotate a turbine to generate electricity. Here's how it works. 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 seawater—pumped through a second heat exchanger—condenses the vapor back into a liquid, which is then recycled through the system.

• Hybrid sistemHybrid systems combine the features of both the closed-cycle and open-cycle systems. In a hybrid system, warm seawater enters a vacuum chamber where it is flash-evaporated into steam, similar to the open-cycle evaporation process. The steam vaporizes a low-boiling-point fluid (in a closed-cycle loop) that drives a turbine to produces electricity.

Advantages:• Low Environmental Impact

The distinctive feature of OTEC energy systems is that the end products include not only energy in the form of electricity, but several other synergistic products.

Fresh WaterThe condensate of the open and hybrid cycle OTECsystems is desalinated water, suitable for humanconsumption and agricultural uses. Analyses havesuggested that Rrst-generation OTEC plants, in the1-10MW range, would serve the utility powerneeds of rural PaciRc island communities, with thedesalinated water by-product helping to offset thehigh cost of electricity produced by the system.A small 1 MW OTEC is capable of producing some 4,500 cubic meters of fresh water per day, enough to supply a population of 20,000 with fresh water.

FoodA further by-product is nutrient rich cold water from the deep ocean. The cold "waste" water from the OTEC is utilised in two ways. Primarily the cold water is discharged into large contained ponds, near shore or on land, where the water can be used for multi-species mariculture (shellfish and shrimp) producing harvest yields which far surpass naturally occurring cold water upwelling zones, just like agriculture on land.

Refrigeration and Air ConditioningThe cold, deep sea water can be used to maintaincold storage spaces, and to provide air conditioning.

Otec useS CLEAN , RENEWABLE , NATURAL RESOURSES.OTEC PLANTS WILL NOT PRODUCE CARBON DIOXIDE OR OTHER POLLUTINGS CHEMICALS.

Desventajas:One of the disadvantages of land-based OTEC plants is the need for a 3 km long cold water pipe to transport the large volumes of deep seawater required from a depth of about 1000 m. The cost associated with the cold water pipe represents 75% of the costs of current plant designs

Another disadvantage of a land-based plant would be the discharging of the cold and warm seawater. This may need to be carried out several hundred metres offshore so as to reach an appropriate depth before discharging the water to avoid any up dwelling impact on coastal fringes (i.e., fish, reef, etc). The arrangement also requires additional expense in the construction and maintenance.

PLANT DESIGN AND LOCATION The location of a commercial OTEC plant has to be in an environment that is stable enough for an efficient system operation. The temperature differential at the site has to be at least 200C (680F). Generally the natural ocean thermal gradient necessary for OTEC operation is

found between latitudes 20 degrees north and 20 degrees south. Land-based OTEC plants do not require a sophisticated mooring system, lengthy power cables and more extensive maintenance as required with open ocean environment. In addition, the land-based sites allow OTEC to be associated with industries such as agriculture and those needing cooling and desalinated water. The offshore or floating OTEC plant is another option. There are a number of difficulties associated with such a facility as it is difficult to stabilise the platform. The need for lengthy cables to deliver power and extra transportation to access the plant are added expenses. The plant is also more susceptible to damage especially during storms.

Descubrimiento reciente:• The discovery that dissolved gases exchange more

rapidly from seawater than from fresh water. This allows for more efficiency and lower costs for open-cycle OTEC and for fresh water production from seawater in a hybrid Kalina Cycle configuration as well as fresh water production in general.

• The development of better heat exchangers and heat exchanger operation with respect to bio-fouling control (on the warm water side) and corrosion control.

Futuro;• Records available from experimental plants demonstrate technical viability and

provide invaluable data on the operation of OTEC plants.  The economic evaluation of OTEC plants indicates that their commercial future lies in floating plants of approximately 100 MW capacity for industrialized nations and smaller plants for small-island-developing-states

• Small OC-OTEC plants can be sized to produce from 1 MW to 10 MW of electricity, and at least 1700 m 3 to 3500 m3 of desalinated water per day.