### Tidal Energy - How Tidal energy works- An introduction

All flowing water carry with them kinetic energy. When such water encounters a turbine, part of the momentum of the flowing water is transferred ton to the turbine, causing it to rotate. The rotation of the turbine cam then be used to generate electricity. So for electricity generation purpose we must know about tidal energy advantages and disadvantages.  Whether the water is om the open ocean, an estuary or a river, its motion can thus be utilized in generating energy. The tides occurring in the oceans are one such source of energy based on the movement of the water. If we analyze the tidal energy pros and cons then we will find that tidal energy is renewable and the output of this energy varies with the variation of the tidal range.

Now How tides are generated ?

• Tides are generated by the gravitational forces of the sun and moon on the oceans.
• by the spinning of the earth around its axis
• and the relative positions of the earth, moon and the sun.

What are tides and tidal current ?
Tides are the periodic vertical rise and fall of ocean water. The period between consecutive high tides is 12.5 hours. The tidal rise and fall of water is accompanied by periodic horizontal and to and fro motion of water called tidal currents. Tides and tidal current is intimately related. So we are already a getting an idea about the pros and cons of tidal power.

Difference between Tidal Energy and Wave Energy

• Tidal energy differs from wave movement. Waves have a period of only about 6 seconds, whereas tides have a period of about 12.5 hours.
• Waves are caused by surface winds, whereas tides are caused by the gravitational forces of sun and moon on ocean water.
Have a look -

The amplitude of tides covers a wide range from 25 cm to 10 m. The speed of the tidal currents is in the range of 1.8 km/h to 18 km/h. The tides and and tidal currents possess renewable energy. The rise and fall of water follows a sinusoidal curve.

1. The biggest advantage of tidal power, besides being inexhaustible, is that it is completely independent of the uncertainty of precipitation (rain). Even a continuous dry spell of any number of years will have no effect whatsoever on the tidal power generation.
2. A great environmental advantage of tidal power generation is - its free from pollution because it does not use in any fuel and also does not produce any unhealthy waste like gases, ash or atomic refuse.
3. Electricity generation from tidal power  do not require large areas of valuable lands because they are mainly on the seashore,
4. Peak power demand can be effectively met when it works in combination with thermal or hydroelectric systems.

Disadvantage and solutions to tidal energy cons

There are a number of reasons why the power generation is still novelty, rather than a normal source of energy, The reasons are -

1. The fundamental drawback to all methods of generating tidal power is the variability in output caused by the variations in the tidal range.
2. The tidal ranges are highly variable and , thus the turbines have to work on a wide range of head variation. This is a great disadvantage of using tidal energy to generate electricity as this affects the efficiency of the plant.
3. Since the tidal power generation depends upon the level difference in the sea and an inland basin, it has to be intermittent operation, feasible only at certain stage of tidal cycle. This intermittent pattern could be improved to some extent by using multiple basins and a double cycle system.
4. The tidal range is limited to a few meters. As bulb turbine technology was not well developed for this range, use of conventional kaplan runners was the only alternative. This was found to be unsuitable. Now, with the development of reversible flow bulb turbines, this difficulty is overcome.
5. The duration of power cycle may be reasonably constant, but its time of occurrence keeps changing, introducing difficulty in the everyday planning of the load sharing grids. This handicap can be removed now with the help pf computerized programming.
6. Sea water is corrosive and it was feared that the machinery may get corroded. Stainless steel with a high chromium content and a small amount of molybdenum and the aluminium  bronzes proved to be good corrosion resistant at La Rance project. The vinyl paint exhibited good results.
7. Construction in seas or estuaries is found difficult.
8. Cost is not favorable compared to the other sources of energy.
9. It is feared that the tidal power plant would hamper the other natural uses of estuaries such as fishing or navigation.