Waves are generated by wind blowing over bodies of water, which transfers some of its kinetic energy to form waves. The size of the resulting waves depend on the wind speed, the duration of time that the wind blows, and the distance over which it blows. The availability of this resource has been estimated to be greater than 2,000 GW world-wide (ref: http://www.wave-energy.net/Library/An%20Overview%20of%20Wave%20Energy.pdf).
Wave power generators use the up-and-down motion of waves to generate electricity. A common method of power generation involves the use of a hydraulic ram to extract energy from the waves.
The Pelamis Wave Energy Converter (ref: http://www.pelamiswave.com) uses the motion of surface waves to generate electricity. This converter is made of connected sections that flex and bend due to the motion of the waves. The relative motion of these sections drives hydraulic rams that pump oil at high pressure through hydraulic motors. These motors are connected to generators and power is generated. The relative motion of the sections can be controlled by restraint of the joints, which can either dampen excess forces such as during storms (to avoid damage), or be “turned-up” to increase efficiency. Each Pelamis unit is typically moored 5-10 km offshore, where water depth is 50-70 meters. In these locations deep swell waves can produce high levels of energy.
According to the claims on their website, each Pelamis P-750 unit is 150 meters long and 3.5 meters in diameter. Each unit consists of three power conversion modules, each rated at 250 kW (total 750 kW) capacity. An offshore wave farm of 40 such units spread out over one square kilometer can produce 30 MW, enough power for 20,000 homes.
Another type of wave power generator is the CETO (ref: http://www.ceto.com.au). Unlike the Pelamis system the CETO is fully submerged, which is perhaps an advantage to some since it cannot be “seen”. Underwater buoys are anchored to the sea floor and move up and down as the ocean swells. This motion drives pumps that pump pressurized seawater through a pipeline and through turbines located on the shore. This is in contrast to the Pelamis system which generates electricity offshore. The CETO units may present greater maintenance (accessibility) challenges since they are located underwater. However, their website indicates that they are less prone to storm damage (since they are submerged) and have minimal mechanical parts, so maintenance requirements may be minimal as a result.
The high pressure seawater can also be used in reverse osmosis machines, to create freshwater. According to their website, any combination of electricity production and seawater production is possible.
Certain areas of the world have great potential when it comes to wave power generation. A large percentage of the world’s population lives near coastal regions, making wave power a very attractive option. Some of the most wave-rich regions of the world are: western seaboard of Europe, northern coast of the UK, pacific coastlines of North and South America, South Africa, Australia, and New Zealand (ref: http://en.wikipedia.org/wiki/Wave_power).
Energy storage is necessary due to the intermittent nature of wave power. Pumped hydro storage facilities, which are a proven technology, can be built on elevated land located near shore, as close as possible to wave power generators. This allows dispatching of power when needed. These pumped hydro facilities can also be used for storing energy from other renewables such as wind turbines (located offshore or near shore), and tidal power generators. Operating together these can provide a reliable level of peak, intermediate and even baseload power to coastal communities.
Links:
http://www.oceanpowertechnologies.com
http://www.finavera.com/en/wave
http://www.wavebob.com