the largest source of untapped energy in the world sits unused except for a pilot project in Hawaii a number of years back. when we start building very large floating islands capable of tapping this souce, we will wonder why we never thought of it before...
OTEC Description
The technology for generating electricity from different ocean temperatures is known as "ocean thermal energy conversion," or OTEC. OTEC makes use of the difference in temperature between the warm surface water of the ocean and the cold water in depths below 2,000 feet to generate electricity. As long as a sufficient temperature difference (about 40 degrees Fahrenheit) exists between the warm upper layer of water and the cold deep water, net power can be generated.
Advantages
OTEC uses clean, abundant, renewable, natural resources. Warm surface sea water and cold water from the ocean depths replace fossil fuels to produce electricity.
Suitably designed OTEC plants will produce little or no carbon dioxide or other polluting chemicals which contribute to acid rain or global warming (the "greenhouse effect"). Extensive research indicates little or no adverse environmental effects from discharging the used OTEC water back into the ocean at prescribed depths.
OTEC systems can produce fresh water as well as electricity. This is a significant advantage in island areas where fresh water is limited.
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.
The use of OTEC as a source of electricity will help reduce the state's almost complete dependence on imported fossil fuels.
The cold sea water from the OTEC process has many additional uses, including air-conditioning buildings, assisting agriculture, and growing fish, shellfish, kelp and other sea plants which thrive in the cold, nutrient-rich, pathogen-free water.
Disadvantages
OTEC-produced electricity at present would cost more than electricity generated from fossil fuels at their current costs. The electricity cost could be reduced significantly if the plant operated without major overhaul for 30 years or more, but there are no data on possible plant life cycles.
OTEC plants must be located where a difference of about 40° Fahrenheit (F) occurs year round. Ocean depths must be available fairly close to shore-based facilities for economic operation. Floating plant ships could provide more flexibility.
Although extensive and successful testing of OTEC has occurred in experiments on component parts or small scale plants, a pilot or demonstration plant of commercial size needs to be built to further document economic feasibility.
Construction of OTEC plants and laying of pipes in coastal waters may cause localized damage to reefs and near-shore marine ecosystems.
Some additional development of key components is essential to the success of future OTEC plants (e.g., less-costly large diameter, deep sea water pipelines; low-pressure turbines and condensers for open-cycle systems; etc.).
The Basic Process
There are basically three types of OTEC processes: closed-cycle, open-cycle, and hybrid-cycle.
In the closed-cycle system, heat transferred from the warm surface sea water causes a working fluid (such as ammonia, which boils at a temperature of about -28°F at atmospheric pressure), to turn to vapor. The expanding vapor drives a turbine attached to a generator which produces electricity. Cold sea water passing through a condenser containing the vaporized working fluid turns the vapor back into a liquid which is then recycled through the system.
Open-cycle OTEC uses the warm surface water itself as the working fluid. The water vaporizes in a near vacuum at surface water temperatures. The expanding vapor drives a low-pressure turbine attached to a generator which produces electricity. The vapor, which has lost its salt and is almost pure fresh water, is condensed back into a liquid by exposure to cold temperatures from deep ocean water. If the condenser keeps the vapor from direct contact with sea water, the condensed water can be used for drinking water, irrigation or aquaculture. A "direct contact" condenser produces more electricity, but the vapor is mixed with cold sea water and the discharge water is salty. That mixture is returned to the ocean. The process is repeated with a continuous supply of warm surface sea water.
Hybrid systems use parts of both open- and closed-cycle systems to optimize production of electricity and fresh water. See the Natural Energy Lab's OTEC Fact Sheet.
http://www.hawaii.gov/dbedt/ert/otec_hi.html
yes and why not put rows of ugly expensive uneconomic but "give u a fuzzy environmental feeling" wind farms all along our coastlines whilst we're at it ?