Wave Energy

It has been estimated that oceans waves have a total power of around 90 million gigawatts (to put this into context, the output of the UK national grid ranges from between 30-50 gigawatts per hour depending on demand). In some places, a potential energy of 70MW per square kilometre are experienced.

Consequently, ocean waves can potentially provide an unlimited supply of renewable energy. Unfortunately, wave power suffers in the same way that wind and solar power suffers in that it is not consistent, making it difficult to match supply with demand. Unlike wind and solar, wave systems can usually generate some power all of the time.

Around the world there are hundreds of research projects investigating wave power and testing various designs of wave power generator to find out the best solutions, with research being carried out with shore-based, near-shore and off-shore systems. Wave generators tend to use a variant of one of four main designs:

Buoyant moored generator

In a buoyant moored generator, the main unit is anchored to the sea bed, whilst a buoy (sometimes known as a duck) floats on the surface, or just under the surface of the sea, bobbing up and down on the waves. A pendulum inside the buoy then converts this movement into electrical energy, with a huge capacitor used to balance out the ebbs and flows of the waves to provide more constant power.

These buoys are typically around 10 metres (33 feet) long. Multiple buoys are used, arranged in set patterns in the sea to take advantage of the wave formations.

Buoyant moored generator

Oscillating water column

A chamber is installed with one end open to the sea and the other vented to an air turbine which is connected to a generator. The waves act like a piston, pushing and sucking the air through the turbine, which powers the generator.

Overtopping generator

Waves create sufficient force to push water uphill. Water is channelled up and over a ramp and into a reservoir that is higher than the surrounding sea levels. This head of water is then used to drive low head hydro-electric turbines.

Hinged contour generator

A hinged contour generator consist of multiple floating tanks that are hinged together and installed in line with the waves. Each hinge is connected to a hydraulic ram. As the waves move across the sea, the hinged contour rises and falls in a snake-like motion, pushing and pulling the hydraulic rams, driving generators to produce electricity.

Hinged contour generator

Hinged contour generators have been in use for a number of years, including in Scotland, off the coast of Orkney. These 750kW Pelamis wave generators, shown below, were the first in the world to be connected to a utility power network. They remain experimental but are probably the type of wave generator that is closest to becoming viable as a mainstream source of renewable energy from waves.

Small scale wave power

Like tidal energy, wave power is an emerging technology. Most of the systems currently in use are still at the experimental stages. There are no systems available to purchase off-the-shelf.

The technical problems that remain to be overcome are similar to those with tidal energy: the units have to be robust enough to survive one of the harshest environments on earth: submerged in salt water and installed in locations with powerful currents. Maintenance and repair is difficult and expensive and ensuring a reliable electrical link has proved to be troublesome.