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A huge dam (called a "barrage") is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam. The ebb and flow of the tides can be used to turn a turbine, or it can be used to push air through a pipe, which then turns a turbine. Large lock gates, like the ones used on canals, allow ships to pass. If one was built across the Severn Estuary, the tides at Weston-super-Mare would not go out nearly as far - there'd be water to play in for most of the time. But the Severn Estuary carries sewage and other wastes from many places (e.g. Bristol & Gloucester) out to sea. A tidal barrage would mean that this stuff would hang around Weston-super-Mare an awful lot longer! Also, if you're one of the 80,000+ birds that feeds on the exposed mud flats when the tide goes out, then you have a problem, because the tide won't be going out properly any more.

Tidal BarragesA tidal barrage is basically a huge dam that is built across a river or estuary. Tunnels are built throughout the dam, and when the tide rises and falls it turns a turbine that generates power. Tidal FencesTidal fences are giant turnstiles that have vertical axis turbines mounted on a fence. The water passes through the fence and powers the turbines. Tidal TurbinesTidal turbines are the latest water power technology used in tidal areas. They look like wind turbines that are lined together underwater. They are used to capture strong tidal flows, so they have to be built extra strong.

Mills using tidal power can be dated back to 12th century Europe,

The steam from the water then increases in pressure, forcing a turbine to spin. The turbine is used to rotate a magnet encased in a generator a high speeds. As the magnet spins, electrons are produced, and they power the electricity grid.

As of 2009, fossil fuels supplied about 85 percent of the world's energy demands.

“true” cost of coal: Depending on how you factor in the costs of climate change, it could be between a few additional cents per kWh to a whopping ¢26.89 extra per kilowatt hour—the high-end estimate from the Harvard study. By way of comparison, the average American paid ¢11.54 per kWh on their residential electric bills last year.

There are three Barrage systems operating throughout the world. One large 240 MW plant on the Rance River in France, and two small plants, one in the Bay of Fundy in Canada, and another in Kislaya Guba in Russia.