Britain runs the rule over wave-power

It is reliable, green and good for the economy. Lucy Shackleton reports on efforts to roll out wave energy in the UK, Ireland, Portugal and beyond.

The UK government announced last month that it was giving planning permission for the world’s first large-scale wave energy farm to be built ten miles off the coast of Cornwall, the south-west corner of England.

The Wave Hub project could generate enough energy for 7,500 homes, according to an economic impact assessment, from the South West of England Regional Development Agency, which is developing the £28 million (€40m) project. It is estimated that the switch from oil or gas-generated electricity could save 300,000 tonnes of carbon dioxide emissions over 25 years, generate up to 1,800 jobs and £569m (€815m) for the UK economy over the same period.

The project aims to provide the infrastructure necessary for companies to develop their wave energy conversion (WEC) devices from the prototype stage to the commercial marketplace. So far, four companies have been chosen to use Wave Hub. These are Ocean Linx, Ocean Power Technology, Fred.Olsen and Westwave. Their WEC devices will all connect to a termination and distribution unit, which will relay the generated electricity, via a sub-sea cable, to a substation on the shore, which will connect to the national grid.

Wave energy, which uses energy collected from waves to drive electricity generators, is a promising sector in the renewable energy industry. In contrast to wind energy and photovoltaics, wave energy conversion usually has low visual and acoustic impact and does not require much, if any, land space. The natural seasonal variability of wave energy corresponds to fluctuating electricity demand in a temperate climate and, perhaps most importantly, wave energy technologies, once built, do not release any polluting emissions. The potential worldwide wave energy contribution to the electricity market is estimated to be about 2,000 TWh a year.

Europe is the world leader in wave energy technology. Countries such as the UK, Ireland and Portugal are keen to exploit their proximity to the strong, regular waves of the Atlantic. Denmark, Norway and Sweden, too, are developing WEC devices.

So far, other WEC device testing facilities have been on a significantly smaller scale. There is a small test site off the coast of Galway, Ireland, but it is not grid-connected. The Portuguese have a 400 kW pilot plant in the Azores. Up to now, the most advanced test site was a European Marine Energy Centre (EMEC) WEC site, off Billia Croo, on the western coast of the Orkney mainland. It was here that the first WEC device, Ocean Power Delivery’s Pelamis (named after a sea snake), delivered power to the national grid. But the Wave Hub installation is considerably more powerful, with a 20 MW capacity as compared to 8 MW at the Billia Croo site. The Wave Hub test site will also be able to test up to 30 WEC devices simultaneously - six times as many as the EMEC wave centre.

Although there are more than 1,000 WEC techniques patented worldwide, there are difficulties with wave energy technologies. Variations in waves’ amplitude, phase and direction make it very difficult to achieve maximum efficiency in energy generation. Harsh weather conditions can cause structural damage to surface technologies. Larger WEC installations may have an impact on marine ecology, fisheries, recreational users and navigation. Environmental impact assessment guidelines have been issued to assist developers to minimise their impact on the environment.

Wave energy is not yet competitive with conventional generation methods, except in isolated communities which are not connected to the national grid. The average price is just below €0.10/kWh, more than double the average electricity price in the European Union. But as WEC technologies develop, the cost of wave energy is forecast to decrease. Coastal regions across Europe are all eager to take advantage of their coastlines and develop the wave energy sector. A sector which Richard Yemm, EV50 nominee and managing director of Ocean Power Delivery, has described as a "huge economic and industrial opportunity, which could run to hundreds of billions of pounds in exports and create tens of thousands of long-term jobs".

Five ways to catch the waves

• Overtopping devices (floating or fixed to the floor): devices capture water from waves and hold it in a reservoir above sea level, before releasing it through low-head turbines which generate power.

• Oscillating water columns (partially submerged): hollow structures which enclose a column of air and a column of water. The water level rises and falls as a result of the movement of the waves, compressing and decompressing the air inside the column. When the trapped air is compressed it escapes from the structure via a turbine. As the water level in the structure drops, air is sucked back inside, again causing the turbine to rotate and generating electricity.

• Floating devices: components are hinged together and react to variations in the sea level. Relative motions of different components are resisted by hydraulic pumps which pump high-pressure oil through hydraulic motors.

• Underwater buoyant devices (moored to the ocean floor): devices which are pushed up and down by variations in water pressure. Energy is used to pump hydraulic fluid through hydraulic pumps.

• Hinged flap devices (moored to the ocean floor): devices which oscillate backwards and forwards according to the movement of the waves. Energy harnessed to pump hydraulic fluid through hydraulic pumps.

It is reliable, green and good for the economy. Lucy Shackleton reports on efforts to roll out wave energy in the UK, Ireland, Portugal and beyond.