Future paths

Waves, constantly moving

Updated 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.

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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.

Average global wave energy resources are 1.3-2 TW, equivalent to total installed electricity capacity worldwide.

The main obstacles to the development of wave energy

Expected efficiency from wave energy is far higher than for wind power. However, there are significant obstacles to using wave energy:

   • Corrosion of submerged equipment;

   • Weakness issues relating to the anchoring of items at sea and to the use of mobile mechanical systems in a highly turbulent environment;

   • Environmental issues: onshore plants can disfigure the landscape, while offshore plants can disrupt fauna, sea traffic and fishing activities.

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.

With efficiency constantly improving, these projects are close to becoming profitable.
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.

True or False ?
France is developing wave energy recovery technology.
True. In France, the Searev7-8 project was launched in 2003 at Ecole centrale in Nantes. This is a second-generation offshore system which uses a closed, sealed floater containing a wheel that acts like a pendulum. The lower half of the wheel, which has a diameter of 9 meters, is weighted with concrete. Waves make the floater oscillate, causing the wheel to move back and forth. The relative movement of the floater and the wheel activates a hydroelectric system that converts mechanical energy into electricity. Hydraulic pumps connected to the pendulum wheel charge high pressure accumulators which discharge their energy into hydraulic engines that drive electric generators. An underwater cable conveys the electricity to land. Measuring 24 meters long and weighing 1,000 tons, one Searev unit will have capacity of 500 kW. Over time, a wave farm will be built, comprising dozens of modules moored to the seabed 30-50 meters below, 5-10km offshore. A 1:12 scale model was tested in 2006 to prove that the theory worked. However, full-scale tests, initially programmed for 2010, have encountered significant delays.

[1] http://www.worldenergy.org/publications/2010/water-for-energy-2010
[2] http://www.inter-mines.org/docs/0904140804PR_090319_DeLaleu.pdf (French) p.55
[3] http://www.inter-mines.org/docs/0904140804PR_090319_DeLaleu.pdf (French) p.56
[4] http://www.pelamiswave.com/videos
[5] http://www.inter-mines.org/docs/0904140804PR_090319_DeLaleu.pdf (French) p.58
[6] http://www.qub.ac.uk/research-centres/WelcometoSustainableDevelopmentatQueens/filestore/Filetoupload,129151,en.pdf
[7] http://www.wavedragon.net/index.php?option=com_content&task=view&id=12&Itemid=14
[8] http://www.inter-mines.org/docs/0904140804PR_090319_DeLaleu.pdf (French)
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