Tidal power projects attempt to harness the energy of tides as they flow in and out. The main criteria for a tidal power generation site are that the mean tidal range must be greater than 5 metres.
The tidal power is harnessed by building a dam across the entrance to a bay or estuary creating a reservoir. As the tide rises, water is initially prevented from entering the bay. Then when tides are high and water is sufficient to run the turbines, the dam is opened and water flows through it into the reservoir (the bay), turning the blades of turbines and generating electricity.
Again, when the reservoir (the bay) is filled, the dam is closed, stopping the flow and holding the water in reservoir when the tide falls (ebb tide), the water level in the reservoir is higher than that in the ocean. The dam is then opened to run the turbines (which are reversible), electricity is produced as the water is let out of the reservoir.
Environmental concerns
The dams built to harness the tidal power adversely affect the vegetation and wildlife. A dam is built across an estuary or bay, allowing the incoming and outgoing waters to flow through small openings fitted with propellers that run electric turbines. To date the numbers of tidal electric plants are limited to forty.
Global/Indian projects
La Rance in France is the only commercial power station operating in the world. In India a major power project costing Rs. 5000 crores is proposed to be set up in the Hanthal Creek in the Gulf of Kutch in Gujarat.
