Waves are a result of the effects of wind on the oceans and seas. This wind originates from the major influx of energy to this planet: solar energy from the sun. The energy contained within waves is around the world is huge; in some places values of 70MW/km of wave front are experienced. In theory it could then be said that huge generating stations could be built which would capture all this energy and supply all or most of our needs. But there are many factors affecting this kind of deployment becoming a reality.
Waves are not as consistent as the tide and therefore there is a definite problem with matching supply and demand. This is one of the main reasons that Wave power has so far been restricted to small scale schemes, no large scale commercial plant is in action.
Identifying areas of suitable wave height is something that has to be done before deployment can start. The highest concentration of wind power is found in the windiest areas, which are mainly between latitudes 40 and 60 in both northern and southern hemispheres. We are lucky in the Scotland to have an abundance of Wave Energy available, mainly on the west coast. The following diagram shows the variation in wave height around Britain during the Christmas Eve, 50 year storm of 1999. The technology must be able to withstand the freak wave heights that can be experienced, in rough and remote locations where access can be difficult.
There are three main categories that wave power can be split into, these are Near Shore, At Shore and Off Shore. There are obvious environmental and social considerations to go with both of these conditions.
Near Shore operations have to consider the aesthetic influence they will have on what could be a picturesque area, they also will have a definite impact on shipping and marine life but again this will be no greater than current offshore installations. It has been suggested that a distance of 12 miles from shore is the distance within which a device is said to be near shore.
The issues discussed previously will also obviously be experienced by off shore wave installations. It has been suggested that a depth greater than 50m will constitute an offshore device.
On shore wave power will have a marked effect on the area it is deployed. There are ways of incorporating it into existing structures to minimise the effect, such as harbour walls.
How much power can you get from a wave?
Linear wave theory assumes that the motion of the water past a point is sinusoidal. The period (T) for one wave to pass this point can be expressed by:
Where, l = wavelength (m) g = gravity = 9.81
The power contained in the wave can be expressed in terms of the length of the wave (kW/m). This is given by the following equation:
Where, a = Wave amplitude (m)
How it works :
here are several methods of getting energy from waves.
One of them works like a swimming pool wave machine in reverse.
At a swimming pool, air is blown in and out of a chamber beside the pool, which makes the water outside bob up and down, causing waves.
At a wave power station, the waves arriving cause the water in the chamber to rise and fall, which means that air is forced in and out of the hole in the top of the chamber.
We place a turbine in this hole, which is turned by the air rushing in and out.
The turbine turns a generator.
A problem with this design is that the rushing air can be very noisy, unless a silencer is fitted to the turbine.
The noise is not a huge problem anyway, as the waves make quite a bit of noise themselves.
Advantages :
- The energy is free - no fuel needed, no waste produced.
- Not expensive to operate and maintain.
- Can produce a great deal of energy.
Disadvantages :
- Depends on the waves - sometimes you'll get loads of energy, sometimes almost nothing.
- Needs a suitable site, where waves are consistently strong.
- Some designs are noisy. But then again, so are waves, so any noise is unlikely to be a problem.
- Must be able to withstand very rough weather.
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