Wave Energy

Wave energy is a largely untapped resource yet the amount of energy in waves around the UK is more than the energy we currently convert to meet our electricity demands. Wave is measured by the rate of energy production in kilowatts per metre of shoreline (kW/m). In the best sites for wave energy, such as the west coast and islands of Scotland, the annual average energy level can exceed 70kW/m.

Today, wave energy research is breaking new ground and is making the advances that wind energy saw 10 to 15 years ago. Scotland has the chance to be at the forefront of this innovation and become a world leader in the wave energy industry.

The energy of waves can be converted into an oscillating motion or into the movement of a working fluid (such as air, seawater or hydraulic fluid) which can be used to drive a generator to produce electricity. There has been a lot of research carried out into the techniques which can harness wave energy. Wave energy can be harnessed in three locations; offshore, near shore and on the shoreline.

There are three basic types of devices to convert wave energy into electricity.

• Devices which channel waves into tapered chambers, or an oscillating water column, whose bottom end is submerged in water. As the waves are funnelled in and out of the chamber, they force air in and out of the chamber. These airflows are in turn channelled through a turbine, which is used to drive a generator. This type of machine is principally designed for use on or near the shore.

• Fixed or semi-fixed offshore devices which make use of the pressure differential in the water that occurs at a submerged point as the wave passes over that point. The pressure differential is used by a variety of means to cause a fluid to flow in a circuit, which is then used to drive a turbine and generator.

• Offshore devices which utilise their buoyancy to cause movement in a part of the device as it moves up and down in the wave. The movement is used either directly or indirectly to drive a generator.

Scotland has a proud history of wave energy research in a number of our universities, who lead the way in the 1970's. This example has now been taken up by a number of Scottish engineering companies. One of the devices in the news recently is the Pelamis which is under development by Ocean Power Delivery Ltd of Edinburgh. The Pelamis consists of a series of cylindrical segments connected by hinged joints.

As waves run down the length of the device and the joints are set in motion, oil is pumped to drive a hydraulic motor. Electricity generated is then transmitted to shore by a common sub-sea cable. The Pelamis is designed to be used offshore; it is a slack-moored device and is around 130m long (about the length of 5 passenger railway carriages) and 3.5m in diameter.

A number of devices have been, or are due to be, tested at the European Marine Energy Centre (EMEC) in the Orkney Islands. This Centre is an important part of the drive to capitalise on our marine resources, and acts as an independent centre where devices can be tested and certified.

Wave energy is also ideally suited for providing electricity needs of island communities, which are usually reliant on diesel fuelled generators. A good example can be found on Islay, where Wavegen operates the world's first commercial sized wave energy device that is connected to the grid.

The unit, called Limpet (Land Installed Marine Powered Energy Transformer), is a shoreline device which uses the principle of an oscillating water column. The Limpet's design is low visibility and has minimal impact on coastal landscapes or views.

Shoreline devices, such as Limpet, and other near shore units are commercially the most advanced and can be particularly advantageous when incorporated into costal protection, harbour development and creating recreational areas for water sports.    

However, wave energy faces a number of challenges before it can reach its full potential and achieve large scale commercialisation. The reality is that a large supply of energy is available, technology exists to exploit this energy and the technical challenges are solvable but the difficulties lie in solving the problems at a cost which is acceptable to the market, and getting the power transmitted from these remote locations to the market demand areas.