Why isn't tidal energy being harnessed?

Question

The energy in tides is enormous, why is it not being harnessed? I know the rate of flow of water is slow, but it takes massive amounts of energy to move water - say into a bay - and then out again.

I would envision building a dam say 1km from shore - we have the technology - just. Then giant gates with turbines attached would generate almost continuous electricity.

Wind power always was a bad idea and is starting to die, as it deerves to. However tides are constant. Water is heavy. Ever built a small dam on a stream at a beach, and been amazed when you let the water out 30 minutes later? If you haven't, you should try it and see the energy.

This can hardly be an original thought, so is it being tried or is there a more fundamental problem? What am I missing?

Answer 1

Tidal power IS going to be harnessed off the coast of Maine I believe. The reason it has not been harnessed more is not because of lack of vision but simple engineering issues. The tidal force will beat up and destroy whatever material we make the 'pistons' with and thus the energy we would get out of it would have to offset the cost of replacing the enormous pistons. Energy generated by wind is MUCH more efficient in terms of cost.

Answer 2

Tidal energy isn't being harness because we lack vision and because most coastal property is privately owned. However, tidal power has been in use for over a millenium on a small scale, and the technology is well known. As you correctly pointed out, tidal power is more reliable than solar or wind power, due to its predictability and consistency.

Answer 3

It has be harnessed in France

search in Google "La Rance"