Harnessing Ocean Energy Through Ocean Thermal Energy Conversion (OTEC), And Tidal And Wave Power.

Oceans have been source of awe for eons and they still continue to be so. Oceans are large stores of energy and are in the focus of various people and organizations to be harnessed. So when I saw this article on Globe-Net explaining the efforts about harnessing this vast resource of ocean energy, I had to write something about this wonderful resource available to most of the countries in the world. According to the United Nations, 44% of the world’s population lives within 150 km of an ocean coast and Canada and Australia the number is much higher at 80%, while in the United States 53% of the population lives in close proximity to an ocean.

There are two main forms of energy easily accessible from oceans are tidal power and wave power - born of the same source, but different in how they turn energy into electricity. The other is the Ocean Thermal Energy Conversion (OTEC), which uses the heat energy stored in the Earth's oceans to generate electricity.

OTEC works best when the temperature difference between the warmer, top layer of the ocean and the colder, deep ocean water is about 20°C (36°F). These conditions exist in tropical coastal areas, roughly between the Tropic of Capricorn and the Tropic of Cancer.

If you look at the figure above, those are the areas with least tidal and wave energy. It also happens to be that most of the countries in these areas (where OTEC could be put to use to harness energy.) So while developed countries like Canada and Australia has much to earn from Tidal and wave energy harvesting, we must not neglect the OTEC or thermal energy harvesting from oceans. As developing countries are unable to spend on research to harness this energy resource, we need to assist them by conducting research for those countries. We need to see beyond borders and treat this as our world rather than segmented pieces of countries in any solution that affects this world but more so in this global warming problem solutions.

OTEC technology is not new. In 1881, Jacques Arsene d'Arsonval, a French physicist, proposed tapping the thermal energy of the ocean. But it was d'Arsonval's student, Georges Claude, who in 1930 actually built the first OTEC plant in Cuba. The system produced 22 kilowatts of electricity with a low-pressure turbine. In 1935, Claude constructed another plant aboard a 10,000-ton cargo vessel moored off the coast of Brazil. Weather and waves destroyed both plants before they became net power generators. (Net power is the amount of power generated after subtracting power needed to run the system.)

In 1956, French scientists designed another 3-megawatt OTEC plant for Abidjan, Ivory Coast, West Africa. The plant was never completed, however, because it was too expensive.

The United States became involved in OTEC research in 1974 with the establishment of the Natural Energy Laboratory of Hawaii Authority. The Laboratory has become one of the world's leading test facilities for OTEC technology.

Technologies

The types of OTEC systems include the following:

• Closed-Cycle

  These 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. Cold deep-seawater—pumped through a second heat exchanger—condenses the vapor back into a liquid, which is then recycled through the system.

  In 1979, the Natural Energy Laboratory and several private-sector partners developed the mini OTEC experiment, which achieved the first successful at-sea production of net electrical power from closed-cycle OTEC. The mini OTEC vessel was moored 1.5 miles (2.4 km) off the Hawaiian coast and produced enough net electricity to illuminate the ship's light bulbs and run its computers and televisions.

  In 1999, the Natural Energy Laboratory tested a 250-kW pilot OTEC closed-cycle plant, the largest such plant ever put into operation.

• Open-Cycle

  These systems use 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.

  In 1984, the Solar Energy Research Institute (now the National Renewable Energy Laboratory) developed a vertical-spout evaporator to convert warm seawater into low-pressure steam for open-cycle plants. Energy conversion efficiencies as high as 97% were achieved. In May 1993, an open-cycle OTEC plant at Keahole Point, Hawaii, produced 50,000 watts of electricity during a net power-producing experiment.

• Hybrid

  These 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 produce electricity.

You can read more about Tidal and Wave energy harvesting here.

Tags: global warming, ocean energy, Ocean Thermal Energy Conversion, OTEC, Tidal energy, wave energy, wave energy harvesting, Tidal energy harvesting, thermal energy harvesting