What is Tidal Power?

Michael Anissimov
Michael Anissimov

Tidal power harnesses the power of the tides to turn a rotor or generate electricity. Mankind has been harnessing this power since at least Roman times, when tidal mills were made to grind grain. Tidal mills work by being set up next to a small dam near a small tidal inlet or estuary. As the tide rises, the dam is left open, and the water rises through it, building up on the other side. Then, as the tide reaches its maximum extent, the door of the dam is brought down and the water is trapped. The tide falls, and when it reaches a suitable level, a small channel in the dam is opened up and the water flows out, through a waterwheel, which can then be used to grind grain.

The Moon's gravitational influence on the oceans of the Earth gives tidal power its energy.
The Moon's gravitational influence on the oceans of the Earth gives tidal power its energy.

Modern tidal power devices operate on a much larger scale, though they have only found limited use in electricity generation so far. Still, tidal power is much more reliable than wind energy and solar power, and more recently there have been several new design and deployment initiatives of tidal power generators.

Tidal power gets its energy from the gravitational influence of the Moon on the oceans of the Earth. As the Moon orbits the Earth, it pulls the oceans towards it slightly, leading to tides with ranges between a few meters (~10 ft) to 16 meters (53 ft) in extreme cases, like the Bay of Fundy at the eastern coast of Canada. This energy can be exploited by tidal power generators in a number of ways.

There are two main types of tidal power generators: tidal stream systems, which exploit the kinetic energy of tides, using water to power turbines in a similar way that windmills use air to power turbines. The other main type are barrages, which operate on a principle similar to tidal mills, operating as a wide dam across an inlet or estuary. Barrages suffer from high cost, environmental issues, and a worldwide limit of viable sites, while tidal stream systems avoid these issues. A lower-impact variation on the barrage is a tidal lagoon, which only covers a portion of an inlet. Another advantage is that tidal lagoons can be configured to generate power continuously while barrages cannot.

Tidal stream generators, the lowest cost-to-entry and most viable tidal power technology, was only developed recently, so it makes sense to say that this new power generation method has just begun to be exploited, and may have quite a future ahead of it.

Michael Anissimov
Michael Anissimov

Michael is a longtime wiseGEEK contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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Discussion Comments


@GiraffeEars- It is funny that you mention tidal hydroelectricity. I was recently in Strangford Loch in Northern Ireland, where I saw an actual tidal generator in action. It looks like a red light tower sticking out of the water with a wake following behind it. I was told by someone I met on my way to Portaferry that it was actually the top of a underwater tidal mill that produces enough electricity to power 1000 homes. The tidal generator is supposedly very low risk t the local ecosystem because the blades spin slow enough that all sea life in the area can move out of their way. If you are ever in Northern Ireland, you should ask about the tidal generator in Stangford Loch.


@Glasshouse- Tidal Stream systems do not refer to the harnessing of the power of streams or rivers, rather it refers to the harnessing of power from ocean currents.

The technology uses what would be the equivalent of underwater windmills situated off the coast in areas where heavy currents exist. Each tower has two to six turbines with short, stiff blades that can change direction with the current.

The benefit over this type of tidal power compared to tidal barrages is that there is very little environmental impact. The turbines are situated off the coast in the open ocean. According to early research, these systems will likely be able to produce 1MW of energy per tower at an estimated cost of 7-12 cents per kWh. This is almost cost competitive with nuclear and natural gas in most places. Imagine if they could combine these tidal turbines with off shore wind turbines, maximizing the power output of these systems.


How exactly does a tidal stream generator work? Wouldn't tidal power systems have a greater impact on the environment than wind and solar? I know that a big problem with hydroelectric power is that it creates a backup of silt that destroys upstream ecosystems and starves downstream ecosystems of nutrients. It would seem like tidal power plants could pose a danger to the fragile reefs that support over a quarter of ocean biodiversity. Does anyone have any thoughts on this?

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