As anyone who has ever been seasick knows, there's a lot of energy in ocean waves. Waves are generated by the wind as it blows across the ocean surface. They travel great distances without significant losses and so act as an efficient energy transport mechanism across thousands of kilometres. The energy can be captured by various devices, which produce enough movement either of air or water to drive generators that converts the energy into electricity.

The ocean surface is nearly always in motion, so wave energy can be produced at a more constant rate than wind or solar energy. It also can be located near where most people live, on the coastline.

The economically exploitable resource varies from 140-750 TWh per year for current designs of devices when fully mature and could rise as high as 2,000 TWh/year, if the potential improvements to existing devices are realised. Global electricity consumption is about 15,400 TWh/y, hence wave energy could supply up to 13% of current world electricity consumption which is equivalent to about 70% of what is currently supplies by hydroelectric schemes.

The first serious study of wave energy took place in the late 1970s when several governments undertook national research programmes as a response to the emerging oil crises. Since the late 1990s a number of small companies have tried to develop and commercialise a range of different wave energy technologies as a non-polluting source of energy, which has resulted in a number of full-size devices being deployed in the sea.

Wave energy systems can be divided into three groups, shoreline devices, near shore devices and offshore devices.

Shoreline devices are fixed or embedded in the shoreline, having the advantage of easier installation and maintenance. In addition shoreline devices do not require deep-water moorings or long lengths of underwater electrical cable.

Near shore devices are deployed at moderate water depths, at distances up to 500 m from the shore. They have nearly the same advantages as shoreline devices, being at the same time exposed to higher power levels.

Offshore devices exploit the more powerful wave regimes available in deep water. Two promising designs include the AquaBuOY system and the Wave Dragon.

In September 2008 the world's first commercial-scale wave-power station was deployed, off the coast of the northern Portuguese town of Aguçadoura. The Pelamis project will generate clean electricity for more than 1,000 family homes in its first phase. The station will eventually be expanded with a further 25 Pelamis machines so that it can generate up to 21MW of power.

Currently this technology is not deemed viable for deployment in the Mediterranean Sea although it is hoped that with better energy harvesting systems this technology will become more attractive as an alternative energy source for coastal towns and cities.