Wave energy is power produced by harnessing the action of the ocean tides. The tide moves in and out twice a day. As it does it moves massive amounts of water and energy with it. This is a plentiful supply of energy but it is not that easy to convert it into electrical power for every day use.
The largest tidal power station in the world is in the Rance estuary in northern France. Around the world about 20 sites have been identified as being suitable for the erection of tidal power stations. However, wave energy is not a perfect solution and it has important disadvantages. But before we discuss these let’s take a look at how wave energy works.
The production of wave energy makes use of tidal barrages. This is similar to the way in which a dam is used to create hydro electric power. However, in the case of wave energy the dam needs to be a lot bigger. Tidal barrages are huge dams which are built across a river estuary. As the tide goes in and out, water flows into tunnels in the dam.
The way in which the tide ebbs and flows causes a turbine to turn or (alternatively) to push air through a pipe which turns a turbine. This means that energy can only be generated when the tide is flowing in and out – which translates into about ten hours of power each day. Tides are predictable so other power plants could compensate during times when wave energy is not available.
The production of wave energy has both advantages and disadvantages. Of course one of its main benefits is that once the station is built the energy is free. Another advantage is that it does not produce and waste or greenhouse gases. Wave energy needs no fuel and it can produce electricity reliably. It can also be maintained with very little expense. In the case of offshore turbines and vertical-axis turbines costs are lower and the impacts on the environment are reduced.
The main disadvantage of producing wave energy is that the large dams required are very expensive to build. Such dams also impact on a large area upstream and downstream. Birds and other wildlife that rely on the tidal mud flats to feed will be negatively affected. There are not very many sites that have been deemed suitable for such power stations. Unfortunately wave energy only offers about ten hours of power a day.
In the case of offshore turbines wave energy would be cheaper to produce and less harmful to the environment. There are also far more sites where this type of power station could be built. “Swanturbines” are a kind of turbine based on direct drive. The blades of the turbine are connected directly to the electrical generator and don’t use a gearbox between. It uses a “gravity base” (large concrete block) to hold it to the seabed instead of drilling into the seabed.