Tidal Power Generation

As the tides are controlled by the relative positions of the sun and moon to earth, tidal power generation is a virtually unlimited resource. There are a number of ways to harness tidal power.

Tidal Turbine Power Generation

The first option is to use underwater turbines, similar to wind mills. These can be placed in areas of tidal movement, the turbines generate electricity as the tide comes in and out. As power generation varies with the density of the medium, the same speed of flow in water creates about 10 times the energy of the same sized air turbine.

An example of a tidal turbine generator is SeaGen (main image) which generates 1.2MW and resides in Strangford Lough, Northern Ireland. This location was chosen as it has very fast flowing tidal currents - it is located in a  small passage between the sea and Strangford Lough. As with wind turbines, tidal turbines always require careful consideration when choosing a location. Areas where natural obstructions increase the flow of tidal waters like this are ideal.

Tidal Barrage Power Generation 

Another option for tidal power generation are tidal barrages. These form dams across estuaries, which control the flow of water through turbines. The tidal range needs to be greater the 5 metres for the barrage to be worthwhile. In periods of low electricity demand, the barrage can pump water into the basin (cheap electricity provides power to barrage). The water is then released back into the sea when there is a high demand, and electricity prices are high.

A tidal barrage in the Rance river in France (left) has been operating since 1966 and creates an average power of 68MW. One problem with tidal barrages is they can effect the eco system of an area. Sea life and birds living in estuaries can be affected by changes in salinity of water due to the barrage. It's very likely sea life will be killed if swimming through a turbine where no other options for passage have been created. As there are not many examples of tidal barrages in operation, the environmental impacts are not fully known. Different areas have different ecologies, and may suffer different consequences from a structure of this kind.

Another problem with tidal barrages is they pose considerable costs, and engineering problems in comparison to underwater turbines. Provision for ships passage through the barrage is also required in most cases, which means further engineering hurdles.

Some positives to come out of tidal barrages, is the economic impact on the area. Construction will probably take a few years, boosting the local economy. The estuary may become calmer inland, allowing recreation and sports to be done in the water. The barrage can also form a bridge for local traffic. The main advantage of tidal power generation is it provides a clean form of energy.

Published - Mon 2nd Nov 2009 15:29:06