Ocean waves are caused by the wind as it blows across the sea. Waves are a powerful source of energy.

The problem is that it's not easy to harness this energy and convert it into electricity in large amounts. Thus, wave power stations are rare.

How it works
There are several methods of getting energy from waves, but one of the most effective 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.

A company called Ocean Power Delivery are developing a method of offshore wave energy collection, using a floating tube called "Pelamis".

This long, hinged tube (about the size of 5 railway carriages) bobs up and down in the waves, as the hinges bend they pump hydraulic fluid which drives generators.

Find out more, including an interactive model, videos and technical details at www.oceanpd.com

Another company is called Renewable Energy Holdings. Their idea for generating wave power (called "CETO") uses underwater equipment on the sea bed near the coast. Waves passing across the top of the unit make a piston move, which pumps seawater to drive generators on land. They're also involved with wind power and biofuel.

Find out more at www.reh-plc.com

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 nothing.
Needs a suitable site, where waves are consistently strong.
Some designs are noisy.
Must be able to withstand very rough weather.