The Rance tidal barrage.
A tidal barrage is a way of converting the energy of tides into electric power. A tidal barrage works in a similar way to that of a hydroelectric scheme, except that the dam is much bigger and spans a river estuary. When the tide goes in and out, the water flows through tunnels in the barrage. 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.
A major drawback of tidal power stations is that they can only generate when the tide is flowing in or out – in other words, only for 10 hours each day. However, because tides are totally predictable, it can be arranged for other power stations tp generate at those times when the tidal station is out of action. Another problem concerns the ecological effect that tidal barrages may have the estuaries they span.
The largest tidal power station in the world, and the only one in Europe, is in the Rance estuary in northern France. It was built in 1966.