Tidal energy is energy obtained from changing sea levels (the tide moving from high to low and vice versa.) This renewable energy source has great potential as tides are much more predictable than wind power and solar energy which are not at all consistent (seasons, bad weather, etc...)
There are three main ways to harness tidal power, these are:
Tidal turbines use similar technology to wind turbines, although their blades are much shorter and stronger. So a good way to think of them is as underwater windmills. Basically the water currents turn the turbines, which in turn activate a generator that produces electricity. These systems work best where there are very strong tidal zones (Norwegian and British coastlines.) and although it is still in it's infancy it does show great promise.
The upfront cost of these tidal stream systems is very high and also installation and maintenance is difficult. But it's still cheaper and has less environmental impact than another tidal system which uses barrages.
Tidal barrages are very similar to the Dams in hydroelectric plants, except that they are much larger as they are built across an estuary or bay. The tidal range (difference between high and low tide) needs to be in excess of five metres for the barrage to be workable. As the tide comes in, water flows through the dam into the basin. Then when the tide stops the gates are closed, which traps the water in the basin/estuary.
As the tide goes out gates in the dam which contain turbines are then opened and the flowing water passes through the turbines, thus generating energy.
Tidal barrages have very high infrastructure costs and are very damaging on the local environment. Also construction of such dams is a very lengthy project. A good example of this is the La Rance barrage in France which took over five years to build (it's the largest tidal power station in the world.)
Tidal Lagoons are similar to barrages but have a much lower cost and impact on the environment. They are self contained structures cut off from the rest of the sea.
It works in pretty much the same way as a tidal barrage as when the tide rises the lagoon fills and when it falls the water is then released through the turbines.
• Tides go in and out twice a day. They are reliable and easy to predict, so it's easy to manage positive spikes in energy.
• It's completely renewable
• It produces no emissions
• Upfront capital costs are very high as most of the schemes require massive concrete constructions.
• Tidal power stations only generate electricity when the tide is flowing in or out (ten hours a day)
• Widespread environmental and ecological damage to the aquatic ecosystem.
• Equipment can be damaged by the strong currents and freak waves.
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