Kepler's 'ocean fence' tidal power unit. Photo: Kepler Energy.
Revolutionary 'sea fence' promises tidal power price crash
Alex Kirby & Oliver Tickell
11th August 2015
An new design of tidal power turbines will generate power at a third the price of current technologies, write Alex Kirby & Oliver Tickell, even at a lower price than offshore wind - without endangering marine life.
What's new is that the blades need no enveloping supporting structure. This leads to lower parasitic drag, and hence low power losses and simple, cheap construction with longer rotors across the flow.
A British company has announced plans for an array of unique marine turbines that can operate in shallower and slower-moving water than current designs.
Kepler Energy, whose technology is being developed by Oxford University's department of engineering science, says the turbines will in time produce electricity more cheaply than off-shore wind farms.
It hopes to install its new design in what is called a tidal energy fence, one kilometre long, in the Bristol Channel - an estuary dividing South Wales from the west of England - at a cost of £143m (US$222m).
The fence is a string of linked turbines, each of which will start generating electricity as it is completed, until the whole array is producing power. The fence's total output is 30 megawatts (MW). Each MW can supply around 1,000 homes in the UK.
Peter Dixon, Kepler's chairman, told Reuters news agency: "If we can build up to, say, 10 kilometres' worth, which is a very extended fence, you're looking at power outputs of five or six hundred megawatts. And just to visualise that, it's like one small nuclear reactor's worth of electricity being generated from the tides in the Bristol Channel."
Suitable for shallow water, fish-friendly
The new Transverse Horizontal Axis Water Turbine (THAWT) will use the latest carbon composite technology, and should be suitable for the waters around Britain, as well as overseas.
What's new about the design is that the blades need no enveloping supporting structure. "This leads to lower parasitic drag, and hence low power losses and simple, cheap construction with longer rotors across the flow", says the company.
"This is in contrast to all other transverse horizontal axis turbines on the market, which are limited in their power output by their lack of structural rigidity and consequent limited maximum size."
The basic generating unit comprises two turbines with a central direct drive generator, with only four supporting bearings and three foundation supports required. "As a consequence of this design, the weight of the unit will be significantly lower than that achievable by propeller type units", Kepler claims.
"The simplicity of the design - only one rotating unit, with no yaw mechanism, no complex pitch changing mechanisms and with electrical equipment in a dry column - means that the Kepler turbine arrays will have very significantly lower life-cycle costs than those of first generation machines."
Video: THAWT scale model undergoing testing.
The turbine is scalable to suit different sites. A typical rotor would be 10m diameter and 60m long sited in a tidal flow with a mean depth of 20m. Tests indicate that the basic 10m diameter, 120m long unit with two turbines should generate more than 4.4 MW at a water velocity of 2m/s, and more than 5.2 MW at a water velocity of 2.5m/s. In addition, the unit will operate with reasonable efficiency at low water velocities.
Because the turbines sit horizontally beneath the surface of the sea, they can be sited in water shallower than the 30-metre depth typically required by current designs. And because the water is slow-moving, the company says, fish can safely avoid the turbines' blades.
Although the technology is regarded as environmentally benign, Kepler says it will still undergo a rigorous environmental impact assessment during the planning process to ensure that it poses no significant risk to marine life and to other users of the sea.
And unlike wind power, the power output from each installation will be completely predictable long in advance based on the movement of the tides. It will also be possible to site tidal power farms at different sites around the UK and other coastlines to provide a smooth power output, increasing the value of the energy produced.
New wind projects win planning permission - but as yet, no money
There is more good news for proponents of renewable energy after the UK government - which is no longer encouraging onshore wind and solar energy - gave planning consent for a large offshore wind farm that could provide power for up to two million homes.
The new wind farm is to be built near the Dogger Bank in the North Sea and will have 400 turbines. Its developers, Forewind, say it could create almost 5,000 jobs during construction. However it may not go ahead owing to severe cuts in funding for renewable energy including offshore wind, believed to be driven by the UK Chancellor, George Osborne.
Energy and Climate Change Minister Lord Bourne was bullish about the scheme, however: "Thanks to Government support the UK is the world leader in offshore wind energy. As we build the Northern Powerhouse, we want local communities to reap the benefits of investment and green jobs from low carbon developments like Dogger Bank Offshore wind project."
Earlier this year, Forewind - a consortium comprising SSE, RWE, Statkraft and Statoil - also obtained planning consent for another installation nearby which, with the new development, would form one of the largest offshore wind farms in the world.
But North Sea oil and gas isn't over yet
But the fossil fuel industry is far from abandoning its own interest in British waters as the energy giant BP has announced that it is to invest about £670m (US$1,040m) to extend the life of its North Sea assets.
It said it would be drilling new wells, replacing undersea infrastructure, and introducing new technologies to help it to produce as much as possible from the area, whose future would be secured "until 2030 and beyond."
In his recent budget, George Osborne announced new tax breaks to encourage the complete recovery of North Sea oil and gas. This is also a legal requirement under the Infrastructure Act 2015, passed by the previous coalition government.
In November, however, delegates to the UN Climate Change Convention annual negotiations will gather in Paris to try to conclude an ambitious and effective agreement on preventing the global average temperature rise caused by greenhouse gas emissions exceeding 2˚C above its pre-industrial level.
Last year, the Convention's executive secretary, Christiana Figueres, said the world's long-term goal was to reduce greenhouse gases to zero by 2100 - a target she said would require leaving three-quarters of fossil fuels in the ground. "We just can't afford to burn them", she said.
Alex Kirby writes for Climate News Network.
Oliver Tickell edits The Ecologist.
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