Energy from the. sea

 The energy from the sea can be obtained mainly in three forms:

1. Tidal energy
2. Wave energy, and
3. Ocean thermal energy

We will describe these means of obtained energy from the sea in somewhat detail.

1. Tidal Energy

The rise of sea water due to gravitational pull of the moon is called"high tide" whereas the fall of sea water is called "law tide.' The tidal waves in the sea build up and recede (rise and fall) a day. The enormous movement of water between the high tides and low tides provides a very large source of energy in the coastal areas of the world. 

The tidal energy can be harnessed by constructing a tidal barrage or tidal dam across a narrow opening to the sea.

Durning high tide, when the level of water in the sea is high, sea - water flows into the resvoir of the barrage and turns the turbines. The turbines then generators to produce electricity. And during the low tide, when the level of sea- water stored in the barrage reservoir is allowed to flow out into sea. 

This flowing water also turns the turbines and generates electricity . Thus, as sea water flows in and out of the tidal barrage during high and low tides, it turns the turbines to generate electricity. The tidal energy is not likely to be a potential source of energy in future because of the following reasons:

1. There are very. few sites around which are stable for building tidal barrages (or tidal dams).
2. The rise and fall of sea- water during high and low tides us not enough to generate electricity on a large scale.

2. Wave energy

Wave energy here means 'sea- waves energy'. Energy from the sea is also available in the form of sea waves. Due to the blowing of wind on the surface of sea, very fast sea- waves (or water waves) move on its surface. Due to their high speed, sea - waves have a lot of kinetic energy in them. The energy to trap sea wave energy to turn turbines and drive generators for the production of electricity.

• One idea is to set- up floating generator in the sea. These would move up and with the sea- waves. This movement would drive the generators to produce electricity.
• Another idea is to let the sea- waves move up and down inside large Tubi. As the waves move up, the air in the tubes is compressed. This compressed air then be used to turn a turbine of a generator to produce electricity.

These ideas are only experimental in nature. Models have been made based on these ideas but it will be many years before full-size wave- energy generators can be a visible proposition only at those places where sea- waves are very strong.

3. Ocean Thermal Energy

A very large area of sea is called an ocean. The water at the surface of an ocean gets heated by the by heat of the sun and attains a higher temperature than the colder water at deeper levels in the ocean. So, there is always a temperature difference between the water " at the surface of ocean" and" at deeper levels." The energy available due to the difference in the temperature of water at the surface of the ocean and at deeper levels is called ocean thermal energy (OTE). 

The ocean thermal energy can be converted into a ' usable form' of energy like electricity. This can be done as follows:

The devices used to harness ocean thermal energy are called Ocean Thermal Energy Conversion power plants (or OTEC power plants). A temperature difference of 20°C (or more) between the surface water of ocean and deeper water is needed for operating OTEC power plants. In one type of OTEC power plant, the warm surface water of ocean is used to boil a liquid like ammonia or a chlorofluorocarbon (CFC).

The high pressure vapour of the liquid (formed by boiling) are pumped up to cool the used up vapours and convert them again into a liquid. This process is repeated again and again.

A great advantage of the ocean thermal energy is that it can be used continuously 24 hours a day throughout the year. Another advantage is that ocean thermal energy is a renewable source of energy and it's use does not cause any pollution. Please note that ocean thermal energy is a renewable source of energy and its use does cause any pollution. Please note that wave energy and ocean thermal energy are the two forms in which solar energy manifests itself in oceans. Another point to be noted is that through the energy potential from the sea (tidal energy, wave energy and ocean thermal energy) is very large but its large scale exploitation is difficult at the moment.