Ocean Energy

The various forms of ocean energy are abundant but often available far away from the consumer sites. The world's oceans have the capacity to provide cheap energy. Right now, there are very few ocean energy power plants, and most are fairly small.

The energy of the ocean can be used in three basic ways (Energy Quest, 2007):

■ Use the ocean's waves (wave energy conversion).

■ Use the ocean's high and low tides (tidal energy conversion).

■ Use temperature differences in the water (ocean thermal energy conversion).

Unlike other renewable energy sources that rely on sophisticated technologies and advanced materials, such as PVs, most ocean renewable energy systems are inherently simple, since they are made from concrete and steel. Additionally, most of the ocean systems rely on proven technologies, such as hydraulic rams and low-head hydropower turbines and impellers. The ocean's energy resource is large and well understood. The ocean's energy resource is superior to wind and solar energy, since ocean waves traveling in deep water maintain their characteristics over long distances and the state of the sea can easily be predicted accurately more than 48 hours in advance. Therefore, although wave energy is variable, like all renewable energy sources, it is more predictable than solar or wind energy. Similarly, tidal currents are created because of the interaction of the tides and the ocean floor and are thus very predictable and generally more constant than wind and solar energy. Additionally, the high density of water makes the resource concentrated, so moving water carries a lot of energy (Katofsky, 2008). The disadvantage of ocean systems is the need to apply mechanical systems that must be robust and withstand the harsh marine environment. The various ocean energy systems are described briefly in the following sections.

wave ENERGY

Kinetic energy (movement) exists in the moving waves of the ocean and can be used to power a turbine. These systems fundamentally convert the kinetic energy of the waves into electricity by capturing either the vertical oscillation or the linear motion of the waves. Individual devices range in sizes of about 100 kW to about 2 MW (Katofsky, 2008). In the simple example shown in Figure 1.10, the wave rises into a chamber. The rising water forces the air out of the chamber. The moving air spins a turbine that can turn a generator. When the wave goes down, air flows through the turbine and back into the chamber through doors that are normally closed.

This is only one type of wave energy system. Others actually use the up-and-down motion of the wave to power a piston that moves up and down inside

Air back in

Air out

Air back in

Air out

Direction

Wave

Turbine

FIGURE 1.10 Principle of operation of a wave energy converter.

Direction

Wave

Turbine

FIGURE 1.10 Principle of operation of a wave energy converter.

a cylinder. That piston can also turn a generator. Most wave energy systems are very small and are applied mainly to power a warning buoy or small lighthouses.

TIDAL ENERGY

Another form of ocean energy is called tidal energy. When tides come into the shore, they can be trapped in reservoirs behind dams. Then when the tide drops, the water behind the dam can be allowed to flow, just like in a regular hydroelectric power plant. Tidal technologies can also employ underwater turbines or propellers driven by the flowing water. Such technologies can be deployed in streams and rivers as well.

Tidal energy has been used since about the 11th century, when small dams were built along ocean estuaries and small streams. The tidal water behind these dams was used to turn water wheels to mill grains. Tidal barrage systems are in commercial operation in a few locations, but their further development is questionable because of their environmental impact in blocking off large estuaries (Katofsky, 2008).

Tidal energy works well when there is a large increase in tides. An increase of at least 5 m between low tide and high tide is needed. There are only a few places on earth where this tide change occurs.

Some power plants are already operating using this idea. One plant, the La Rance Station, in France, makes enough energy from tides (240 MW) to power 240,000 homes. It began making electricity in 1966. It produces about one fifth of a regular nuclear or coal-fired power plant. It generates more than 10 times the power of the next largest tidal station in the world, the 17 MW Canadian Annapolis station.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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