Wave and tidal power
The continuous movement of sea water caused by the Earth’s rotation and the pull of the moon has the potential to provide us with an inexhaustible supply of energy.
This takes two forms – wave power and tidal power. Neither has yet been properly exploited in Britain, mainly because other energy sources have so far proven cheaper and easier to develop. But, as easy to reach oil and gas start to run out, global energy demand rises and commitment to limit climate change strengthens, the case for wave and tidal is becoming stronger.
Britain has over 11,000 miles of coastline and some of the highest tidal ranges in the world. With technology developing fast, it is clear that both wave and tidal power can make a significant contribution to energy generation in the future, with tidal stream generators in particular helping us reach our long term aim of a carbon free economy.
Of the two, tidal power is the more developed technology, with some power stations already operating successfully in France and the US. Wave energy generation is still a research field, with many designs being tested and competing to prove they can cope with the demanding challenges posed by harnessing the ocean’s relentless power.
The two leading tidal technologies are barrages and tidal stream generators:
Tidal stream generators
Tidal stream generators are mounted on the seabed or estuary floor, and make use of the kinetic energy of moving water to power a turbine. Often described as submerged wind turbines, tidal stream generators are far cheaper and less ecologically damaging than barrages, and because of the much higher density of water, they produce more energy than a wind turbine of equivalent size. And the energy they generate is more regular because tides are regular and predictable.
Tidal stream generation is still an emerging technology and no standard design has yet been agreed upon, but in the near future it is likely to play a key role in supplying the world with clean, reliable, and completely renewable energy.
A tidal barrage looks something like a dam, stretching across a river estuary. Inside it are a series of turbine wheels, continuously rotated by the constant water flow as the tide rises and falls, generating hydroelectric power. Energy generation is at its height on the ebb tide as the barrage traps water behind it, releasing it slowly and generating electricity.
In Britain we have some of the highest tidal ranges in the world, and the Severn, Humber, Dee and Solway estuaries are all suitable sites that could generate large amounts of power – but there are problems.
The Severn Barrage
Barrages are expensive and take years to build. Given the urgency with which we need to move to clean energy sources to tackle climate change, they are not currently the best way to spend our money.
So when the government rejected proposals for a Severn barrage in October 2010, Greenpeace didn’t object but called on the government to invest the money in other more cost effective renewable energy projects. The scheme would have cost in the region of £30bn – money that we think would be better spent developing Britain’s offshore wind industry, where an investment of less than half that magnitude would generate more usable power and far greater economic returns.
And there’s another problem. Estuaries are among the world’s most productive and sensitive ecosystems, and the flooding by these barrages causes great disruption to their natural processes. The environmental impacts in and around the Severn, for example, could have far-reaching consequences – making it difficult to approve the project.
This doesn’t mean that tidal barrages are never an appropriate solution, simply that each project has its own set of economic and environmental issues, so they are best considered on a case-by-case basis.
Wave energy can be captured in many ways, including anchored offshore devices pitching back and forth or up and down over the waves, or fixed onshore installations using the waves to drive a turbine.
Waves lose their energy in shallow water because of friction as they interact with the seabed, making the best place to site wave generators at the edge of the continental shelf, where the shoreline drops steeply down and the deep ocean begins.
Wave technologies have only been available for a few decades, but a Centre for Alternative Technology report estimates it could eventually meet 10 percent of Britain’s energy needs.
But there are still big challenges to be overcome – it can be difficult to convert a slow, oscillating and choppy wave motion into electricity. And the ocean is the toughest of environments – generators are constantly exposed to corrosive salt water and may be regularly battered by violent storms.
British companies and universities are at the forefront of developing this technology, backed by grants from the £50 million Marine Renewables Deployment Fund. They are attempting to harness the awesome power of the Atlantic Ocean where the kinetic wave energy is greatest – around Northern Scotland and Cornwall. The European Marine Energy Centre in Orkney has been central to the development of Pelamis Wave Power’s P2 energy converters, which look strong candidates to provide the first workable commercial wave farms.
In 2010 the South West Regional Development Agency installed its Wavehub marine energy project 16 miles off the Cornish coast. Wavehub is connected to the national grid, allowing scientists and engineers to test their wave generators in a real-world environment.
These exciting projects are starting to demonstrate the potential of both wave and tidal stream technologies. To hit the UK’s 2050 target to reduce carbon emissions by 80 per cent, we’re likely to need one or more of them, or some other practical design, to be commercially viable well before that date. And that, as ever, will require genuine government commitment, in the form of supportive policies and development funds.