The Tide is Nigh

18 February 2008

seatrials
Photo credit Pelamis Wave Power

Britain is blessed with an abundance of potential renewable sources of energy.  Besides wind, there is also wave and tidal stream power.  This is an industry in its infancy, despite being a source of electricity going back to the 1970s, because finance and innovation have not been forthcoming.  If the German wind industry is a guide – the UK is in a position to create jobs and profits by being at the cutting edge of a new technology.   In Germany a quarter of a million jobs have been created through the design, manufacture and maintenance of wind turbines. 

According to CAT Development Director Paul Allen, Britain has enormous potential for marine renewable energy generation. Tim Ovens, project director of The Renewable Energy Centre agrees:  “Because of our long coastline, this is a potentially huge resource.” The waves and tides which buffet our shores could account for up to 15% of our electricity requirement.  New engineering techniques, and job creation in areas of high unemployment like Cornwall and Scotland could be of considerable benefit to the UK economy.

How does it work?

Wave energy occurs because the wind drags across the surface of the sea, forming waves.  The stronger the wind and longer it blows the more energy it imparts.  For this reason the waves along the West coast of Britain are more powerful and energy-rich as they come from the Atlantic Ocean than those on the East coast
Tidal Stream energy comes from the way the gravity of the sun and moon affects water.  Unlike some renewables, Tidal streams are completely predictable – happening twice a day, and can carry large amounts of energy.

What are the latest developments?

seatrials
Photo credit Pelamis Wave Power

Sea snake-like wave machine Pelamis generates power by the wave motion pumping fluid through hydraulic rams, which drive hydraulic motors which then drive electrical generators. The resulting power is sent to shore via a seabed cable.  Several 140 m long Pelamis devices can be linked together.  Each machine is rated at 750kW, enough to power 500 houses.  Depending on the wave resource, machines will on average produce 25-40% of the full rated output over the course of a year.

Three Pelamis wave machines are being tested commercially at sea off the coast of Portugal. Another four are planned to be installed at the European Marine Energy Centre (EMEC) in the Orkneys. The UK Government and other public sector organisations have invested around £15 million in the creation of the centre and its two marine laboratories, one for wave power, the other for testing tidal stream technologies.
The Carbon Trust estimates that the coasts of Britain are one of the richest sources of tidal stream energy in the world.  Because this technology is in its infancy we do not know yet what is the best type of machine to extract this energy - horizontal axis turbines, vertical axis turbines, oscillating hydrofoil machines and venturi-based devices (a tube that increases the speed of the water-flow) have been proposed.  Once it is determined which is the best design, not just in terms of energy produced, but also low-maintenance and minimum environmental disturbance, then they can be rolled out (or rather sunk) around the coast.

seatrials
Photo credit Pelamis Wave Power

Another project is the Cornwall Wave Hub.  It is a module for connecting wave and tidal generation devices to the shore.  Essentially it’s like a marine version of a home extension socket – the devices are plugged into it and the cable leads to the mains.  This makes testing wave devices much simpler, because they do not have to build an electricity sub-station.  Nor do they have to install the monitoring capability each time a new device is linked.  This will speed up testing, as well as making the results uniform so which is the best technology will be apparent. The devices attached to the Wave Hub could generate enough electricity for 7,500 homes, directly saving 300,000 tonnes of carbon dioxide over 25 years. An independent economic impact assessment commissioned by the South West Regional Development Agency has shown that Wave Hub could create 1,800 jobs and £560 million for the UK economy over the same period.

What are the environmental dangers?

Any intervention into nature has effects.  We have become more aware of how all our technologies have environmental consequences, and these new marine energy systems will be carefully sited to reduce the adverse effects.  It is unfortunate that the government currently favours the large and intrusive Severn Barrage, which has given rise to opposition because of the disruption it will have on the local ecosystem.  Other devices such as the wave hub and Pelamis will have potentially much smaller environmental disturbance. The Cornwall Wave Hub is intended as a test bed so that we can research the energy generation potential of new inventions, and also their environmental impact, in a real situation, rather than a laboratory.

Paul Allen of CAT believes that the problems of deploying these systems are not technological ones, but: “the political will and cross-party consensus. It’s not an engineering challenge, but a social and political one.  Look how mobile phones changed from something the size of a brick to something the size a matchbox. The technological innovation is there.  And there is enormous jobs potential, but the government needs to set real incentives.”

Links:
Images of devices: http://www.bwea.com/marine/devices2.html
CAT:  Centre for Alternative Technology http://www.cat.org.uk/
The Renewable Energy Centre  http://www.therenewableenergycentre.co.uk/
Pelamis Wave Power: http://www.pelamiswave.com/
EMEC: http://www.emec.org.uk/

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