As Jon mentioned on his previous post, there are three ways of generating electric energy from tides (one of them only works theoretically).
In today´s post, we are going to talk about the most common one: tidal barrages. Usually they are placed on narrow bays or estuaries. The barrages use the difference of seawater level generated between their sides to generate electric power thanks to the motion of some turbines. A noticeable fact is that tidal power stations are only worth-building on those places where the difference between the high and low tide is at least of 5 meters. Those tidal power stations basically work as the ones we traditionally find in rivers: when the tide comes in, sluice gates are opened, so the water can flow into. When the accumulation of water reaches its maximum level, sluice gates close. The machine operators keep them that way until the low tide. This point is the optimum for energy conversion (maximum seawater level difference). Sluice gates are opened and the water flow makes the turbines move, which connected to some generators, produce the electricity.
Example: Rance’s power station (France). Remarkable facts:
– Around its dam, apart from turbines and generators, there are also some rooms with extra machinery and control gadgets, where operators of the station work.
– A total amount of 24 reversible turbines and 24 generators. The turbines reach 5700 revs per minute, achieving a maximum power of 240 MW.
– The water flow is about 20 000 m³/s.
Let’s focus on the benefits and drawbacks of tidal barrages:
– Clean and predictable energy source.
– It is not oil dependent.
– The dam can link up different cities and work as a new road for trains or traffic.
Among the drawbacks…
– The tides and the electricity demand are not related, which is a problem due to the difficulties found in energy storage.
– Ecosystems can easily be altered.
– Introduction of difficulties in shipping.
On future posts, we will go on explaining the remaining methods: Tidal Stream Generators and Dynamic Tidal Power.