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Wave Energy

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There’s so much energy in the ocean waves that researchers believe that if just 0.2 percent of the ocean's power can be harnessed it would be enough to power light bulbs around the world. That is yet to happen because it’s a difficult technology to develop and the sea is often not very hospitable. The waves are not as consistent as the tide and create problems of matching supply and demand. However, computer modeling has made it easier to simulate the ocean, and thereby develop designs and ideas. But the vast majority remains on paper.

Among the pioneering projects is a deal the USA’s largest utility, Pacific Gas & Electric [1], has signed with the Canadian firm Finavera Renewables [2] to purchase power generated with this cutting-edge technology. The initial 2-megawatt project, to be constructed about 2.5 miles off the coast of Eureka, California, will supply electricity to customers onshore in northern and central California. With conventional energy one megawatt powers about 750 homes. But as wave power will be intermittent, the amount of electricity delivered is expected to be somewhat less. See a Finavera film on its technology Finavera Renewables’ AquaBuOY [3] on You Tube.

Contents

[edit] Under-Utilized Power Potential in the Sea

Waves breaking on the world’s coastlines are estimated to contain 2 to 3 million megawatts of power. In favorable locations, wave energy density can average 65 megawatts per mile of coastline.

With so much potential power in the sea why has it not been captured to meet all our needs? Development of wave energy is 15 to 20 years behind wind energy, which is now finally beginning to optimize its production technologies. Here too, like wind energy, the costs are very high in the early stages, but will gradually settle down.

Identifying areas of suitable wave height is something that has to be done before deployment can start. Wave heights can vary and rough and remote areas may be difficult to access. Available technology must be able to withstand such problems.

[edit] How Wave Energy is Created

The conversion process of waves into energy usually makes use of either mechanical motion or fluid pressure. Some of the techniques used are oscillating water/air columns, hinged rafts, gyroscopic/hydraulic devices. The mechanical energy is then converted to electrical power using a generator.

There is plenty of water and waves, but limited technology to convert them to energy. The motion and power inherent in ocean waves have to be harnessed to create wave energy. The waves of the ocean roll on the shore with the force of the wind blowing across the surface of the sea. Power is created by harnessing this movement of the ocean waves.

Wave energy is generated by the movement of devices, either stationary or floating on the surface of the ocean and moved by waves, as opposed to a large volume of tidal water, which is used to drive motors. Wave energy can then be converted into electricity by wave power machines and deployed either on the shoreline or in deeper waters offshore.

[edit] Power Generation Devices

Shoreline Devices

As these are embedded in the shoreline, maintenance and/or installation are easier. Such devices also do away with deep water moorings or long lengths of underwater electrical cable. However, they would experience a much less powerful wave regime. The deployment of such schemes could be limited by requirements for shoreline geology, tidal range, preservation of coastal scenery, etc.

One major class of shoreline device is the oscillating water column (OWC).

• Open Oscillating Water Column (OWC)

Uses a column of water as a piston to pump air and drive a turbine to generate power. Once floated on the surface of the ocean, this device converts the slow and sudden powerful waves into faster but less powerful air currents to push the air turbine. Special kind of turbines are used which can turn in the same direction no matter where the air is coming from. A ‘closed’ OWC is submerged into the ocean and fixed onto the seabed from where it uses differences in water pressure between each wave crest.

[edit] Offshore Devices

Such devices do not exploit the more powerful wave regimes available in water of over 40 meter depth. These devices are made to float on the surface and so they usually require flexible moorings and electrical transmission cables. Popular devises used are:

• Hinged Contour Device

This type of device follows the motion of the waves. It creates power using the motion at the joints. It is commonly moored slackly to hold it in place. Alternate motion of the waves creates resistance to the waves. The alternate motions raise and lower different sections of the machine relative to each other, pushing hydraulic fluid through hydraulic pumps to generate electricity.

• Float or Pitching Device or buoyant moored device

The device is moored to the sea floor and floats on or just below the surface of the water. Power is generated with a wave power machine resisting the motion of the waves. Part of the machine needs to move while another part remains still.

Electricity is generated from the bobbing or pitching action of a floating object which can be mounted to a floating raft or to a device fixed on the ocean floor.

Image:Wave energy.gif

[edit] Benefits

• With the development of wave energy conversion technology it will become possible to produce electricity at a competitive commercial cost without having the risks of pollution

• Plants set up at shoreline can provide electrical energy for local or national electricity grids.

[edit] Challenges Ahead

Wave energy is not only clean and renewable, but the installed devices can act as a barrier and protect buildings along the shoreline. It is free to use and doesn't contribute to pollution or global warming. However, many obstacles have to be overcome before it can be used widely throughout the world.

Though wave energy is present at every ocean and sea it varies widely. In spite of producing high pressure there is difficulty in creating electricity because of low speed. They also move in many directions, posing further obstacles.

If mechanical structures are unable to withstand the stresses of the sea it would result in unreliable energy. Because of these reasons today harnessing wave energy is less viable than fossil fuels such as oil and coal. This is also the reason for limited investment in research or infrastructure.

Though slow, there has been progress and confidence that technology and the economics of renewable energy will become much more attractive in the next couple of decades.

REFERENCES:

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