Buoyant future

Plans in the west country to install an electrical hub on the seabed could provide a much-needed boost for the burgeoning wave power industry.

Wave power machines connected to an underwater electrical socket could be providing power to the national grid by 2006 according to proposals laid down by the south west’s Regional Development Agency.

It has just invested almost half a million pounds to take forward plans for the installation of such a device, known as the Wave Hub, in the seabed off Cornwall’s Atlantic coast. It’s hoped that the hub will enable manufacturers of offshore wave power devices to test how effective their machines are before moving on to commercial production.

While up to 18 companies are said to be interested in working with the hub, there are three clear front-runners: Plymouth’s Orecon, Edinburgh’s Ocean Power Delivery and Denmark’s Wavedragon. Each company has developed a dramatically different approach to harvesting wave energy.

Orecon, being a local company, is naturally one of the most enthusiastic about the plans. Formed in 2002 as a spin-out from the University of Plymouth, Orecon is something of a champion for the south west wave power industry. Indeed, the company’s managing director Fraser Johnson claimed that it’s partly thanks to the agitation of his company that the Wave Hub project has seen the light of day.

Johnson is delighted that finally something on the wave power front appears to be happening in the south west. Referring to initiatives north of the border – such as Orkney’s marine energy test centre – Johnson said: ‘Scotland is a great place to go; lovely people, great wave resource, but a lousy grid.’

He added that while it would cost millions to install a grid infrastructure to get power from the outer Hebrides to anywhere useful, Cornwall has a ‘wonderful grid’ and equally useful wave resources.

To illustrate his point, Johnson revealed the proposed location of Wavehub: 250m off-shore from an old coal-fired power station at Hale. He explained that the sub station is still in operation and provides a link to one of the main arteries coming into the south west. It is precisely this kind of existing infrastructure that Scotland lacks, he said.

Orecon’s technology is basically a refinement of the single oscillating water column (OWC) systems used in other wave-power systems. In a typical OWC system, waves flow in and out of a vertical column floating in the water. When a wave enters the column, it compresses the air inside the system and passes it across an enclosed turbine. As the wave recedes and the water leaves the chamber, the air is sucked backwards past the turbine for a second time.

The problem with such a system is that single OWC units have to be ‘tuned’ to operate within the frequency characteristics of a particular type of wave and outside a small frequency bandwidth; either side of this and their efficiency drops sharply.

Orecon’s device, the MRC1000 (multi-resonant converter with a generation capacity of 1MW) gets round this efficiency problem by using a group of six tubes of different lengths linked to a single air turbine. Each of these tubes can be tuned to a different wave frequency, thus making the system more efficient than its OWC forbears.

Johnson said that another advantage of the system is that most of the technology involved is standard offshore equipment used in the oil and gas industries. This should reduce the cost of commercial deployment and ensure that the units are robust enough to operate for long periods with minimal maintenance. As for the environmental impact of the device, Orecon has an environmental arm that examines the potential impact of its devices at the early design stage.

He said that it’s somewhat surprising how many wave device manufacturers fail toconsider this. Orecon is currently seeking funding to take the idea forward.

Edinburgh’s Ocean Power Delivery is ideally placed to exploit existing wave research resources. Following successful sea trials, the company expects its Pelamis generator to be generating grid electricity at Orkney’s European Marine Energy Centre (EMEC) within the next couple of months. It is also extremely excited about the opportunities offered by Wave Hub.

The Pelamis, also called the sea snake, works on a different principle to Orecon’s device. The semi-submerged, articulated structure is composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams, which pump high-pressure oil through hydraulic motors that drive electrical generators to produce electricity.

Power from the joints is then fed down a cable to a junction on the seabed. OPD’s business development director Max Carcas said that several devices could be connected and linked to shore through a single seabed cable.

Like Orecon’s device, Pelamis can exploit varying wave conditions. A novel joint configuration allows the system to be ‘turned-up’ in calm seas where capture efficiency must be maximised, or down to limit loads and motions in rough conditions.

Carcas is as enthusiastic as Johnson about Wave Hub. He said that the attraction of the project lies in the fact that it removes the previously prohibitively expensive hurdles of building an infrastructure and will allow wave generator manufacturers the freedom to concentrate all of their efforts on their core technology.

The Pelamis concept has been proved with both scale models, and a land-based version of the power module that uses hydraulic actuators to simulate north Atlantic wave conditions. The company has also had a full independent design verification carried out by offshore consultant WS Atkins.

Pelamis is now being prepared for sea trials on the quayside in the firth of forth, following which the system will be towed in sea trials. Then, assuming the trials have been successful, the device will be deployed in Orkney.

Finally, there is Denmark’s Wave Dragon, which enjoys the distinction of being the first offshore generator in the world to actually produce power for a grid. Indeed, the first prototype connected to the grid has been generating power in the Baltic since May 2003.

Wave Dragon is perhaps the simplest of the systems. Described by its creator as an ‘overtopping device’, the system uses two ‘wave reflectors’ to direct waves up a ramp and into a reservoir above sea level. This water is then let out through a number of turbines and is transformed into electricity. Despite its groundbreaking status, some have questioned the huge displacements required to make Wavedragon work efficiently.

It can be deployed in a single unit or in arrays of two to 200, resulting in a power plant that its developers said could have a capacity comparable to traditional fossil-based power plants.

The machine is currently being reviewed by the UK Carbon Trust with the aim of lowering production costs and accelerating the process towards commercialisation.

Talking to people involved in the wave generation industry is an unusually refreshing experience for a seasoned observer of the manufacturing industry.

For here are qualities so frequently missing: optimism, excitement, and the unbridled enthusiasm that comes from the knowledge that this technology could make the world a better, cleaner place. After teething troubles, caused largely by a lack of funding and political commitment to the idea, wave power seems finally to be takingthe first step towards becoming a significant power source for the 21st century.

Some grandiose claims concerning the amount of power it can provide are made for wave power. and, possibly, if we surrounded our entire coastline with wave generators the claims could be realised. It seems though, that the true promise of wave energy, and its most likely contribution to our power needs, will be when it is harnessed in tandem with the wind and the sun.