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- The energy of the oceans
Waves, constantly movingUpdated 02/18/2014, published online 05/28/2013
At sea, the force of the waves is considerable and omnipresent. Their theoretical power far exceeds that of wind energy. However, not every country has the same potential. Those with the best exposure have developed different wave energy recovery techniques.
Renewable, dense energy accessible all over the world
Wave energy is a significant source of raw energy. It is one of the densest (or energy-rich) renewable energy sources. The amount of energy generated by waves is small (1 W/m² per year, 200 times less than direct solar energy), but it is multiplied by the huge surface area offered by the sea for recovering this energy. According to the World Energy Council1, average global wave energy resources are 1.3-2 TW, equivalent to total installed electricity capacity worldwide (about 2 TW).
Although present along the coasts of all oceans worldwide, some areas have more wave energy than others, such as the North Atlantic, where power is 45 kW/m, and particularly so off the coasts of Britain and Ireland. In France, its potential is about 40 TWh/year2.
Expected efficiency from wave energy is far higher than for wind power. However, there are significant obstacles to using wave energy:
A variety of techniques
There are several types of wave energy recovery systems3:
• Onshore oscillating water columns capture the incoming waves. Water enters a chamber where it compresses the air, driving a turbine which in turn drives an electric generator;
• Submerged oscillating water columns are underwater buoys that rise and fall, tossed around by the waves. Anchored to the seabed, their movement activates a piston, draws seawater into a turbine or compresses air or oil that then drives an engine which in turn drives an electric generator;
• Tapered channel systems funnel waves into a channel that gets progressively narrower, causing the waves to rise and spill over the channel walls into a reservoir, gradually filling it up. The water in the reservoir then flows back to the sea through a turbine, generating electricity in the process. The reservoir can be located onshore or offshore on a floating, slack-moored platform;
• Pendulor devices are arrays of boxes linked by articulated hinges that bob up and down on the waves. Energy is recovered through the joints between each box using pistons that activate pressurized oil pumps.
Large-scale European projects
The development of wave energy technology has been ongoing for over 20 years. As yet little used in France, it is being developed in a number of European countries that are already using second-generation offshore technology, in Scotland and Portugal for example.
• The Pelamis project4, an array of pendulor devices. Launched in Scotland in 1999, the initial project provided for a facility of 30-40 Pelamis distributed over 1 km² of ocean and supplying electricity to 20,000 homes. To date, only tests to connect to the land-based power grid have been carried out, in 2004. A further two Pelamis projects are underway in the United Kingdom (the Orkney Islands and southern Wales). A Pelamis was also in operation since 2008 in Portugal (comprising 3 "snakes") but problems with the prototypes in 2009 led to the devices being brought ashore for repairs and the operator went bankrupt, meaning that the project has now been suspended indefinitely;
• The Limpet project5 on the Isle of Islay (Scotland) has been tested since 2000. It uses onshore oscillating water column (OWC) technology and has capacity of 500 kW;
• The Wave Dragon6 prototype was launched in Wales in 2007. This uses floating, slack-moored platform technology and has capacity of 7 MW.
• Other oscillating water column or oscillating float systems are being developed in Portugal, Spain, Brittany and England.