How Does Tidal Power Work?

Tidal barrage diagram showing turbine gates, sluice, and ship lock.

Tidal barrage diagram showing turbine gates, sluice, and ship lock. Image by Evgeni Sergeev. License: GNU FDL

Tidal power generation also known as tidal energy is a renewable energy source that relies on the tides to generate electricity. As you may or may not know the tides are created by the gravitational pull of the moon and to a lesser extent the sun. Changes in water level which affect tidal currents are a result of gravitational attraction. The power of the tide in a specific location is caused by changing positions of the moon and sun, effects of Earth’s rotation, and the shape of the sea floor and coastline.

The stronger a tide is, either from water level change or speed of current, the more tidal energy that can be used to generate electricity. This energy is essentially unlimited although tidal power does actually slow the rotation of the Earth. This slowing occurs even naturally as tides ebb and flow. In the last 600 million years or so the rotation has slowed from 22 hours to 24 hours where it’s at today. Harnessing tidal power to generate electricity would only have an effect on this rotation over hundreds of millions of years though. Therefore it is widely accepted that this shouldn’t cause any concerns. Also, this classifies tidal power or energy as a renewable energy source even though it will technically be exhausted after millions of years.

How does tidal power work to generate electricity? There are many different designs of tidal power generators but overall they share the same goal. A tidal barrage is created at the mouth of a river or other choke point that connects to the ocean. You can think of this as basically a dam. In flood tidal power generation below the water level there are opening in this barrage that have turbines in them. These turbines are powered when the tide goes in or the water level rises.

This way is much less efficient than the other method though which ebb tidal power generation. In ebb generation there is a basin which is filled through a sluice until hide tide. Then the sluice gates are closed and you effectively have a dam. There are turbines in a path from the basin back to the ocean and this is kept closed until low tide. Then the turbine gates are opened and the water flows out generating electricity by turning the turbines. This results in a much faster water flow which is important for turbines. It should also be noted ther is a ship lock to allow for boats to move between the two bodies of water. Another reason why this method is more efficient than flood tidal power generation is because the river or other body of water won’t be flowing backwards against the tidal currents, this flow will actually help in an ebb tidal power setup.

Costs of tide power systems compared to traditional power sources is much higher during development but much lower during operation. Unfortunately this means that governments are usually unwilling to help finance tide power stations because of this long investment to return lag. Lately though governments have been realizing the importance of such renewable and alternative energy sources and have begun to pick up funding projects such as tide power generation. Tidal power history is a short one but hopefully the first chapter of many to come.



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