Ocean Power
The Coming Wave

June 5, 2008

Energy: Enthusiasm for renewable energy means wind turbines and solar panels are
popping up all over the place. But what happened to wave power?

You only have to look at waves pounding a beach, inexorably wearing cliffs into
rubble and pounding stones into sand, to appreciate the power of the ocean. As
soaring oil prices and concern over climate change give added urgency to the
search for new, renewable sources of energy, the sea is an obvious place to
look. In theory the world’s electricity needs could be met with just a tiny
fraction of the energy sloshing around in the oceans.

Alas, harnessing it has proved to be unexpectedly difficult. In recent years
wind farms have sprouted on plains and hilltops, and solar panels have been
sprinkled across rooftops and deserts. But where the technology of wind and
solar power is established and steadily improving, that of wave power is still
in its infancy. The world had to wait until October 2007 for the first
commercial wave farm, consisting of three snakelike tubes undulating with the
Atlantic swell off the coast of Portugal.

In December Pacific Gas & Electric, an American utility, signed an agreement to
buy electricity from a wave farm that is to be built off the coast of California
and is due to open in 2012. Across the world many other wave-power schemes are
on the drawing board. The story of wave power, however, has been one of trials
and tests followed by disappointment and delays. Of the many devices developed
to capture wave energy, none has ever been deployed on a large scale. Given wave
power’s potential, why has it been so hard to get the technology to work—and may
things now be about to change?

The first patents for wave-power devices were issued in the 18th century. But
nothing much happened until the mid-1970s, when the oil crisis inspired Stephen
Salter, an engineer at the University of Edinburgh, in Scotland, to develop a
wave generator known as Salter’s Duck. His design contained curved, floating
canisters, each the size of a house, that would be strung together and then
tethered to the ocean floor. As the canisters, known as Ducks, were tossed about
by the waves, each one would rock back and forth. Hydraulics would convert the
rocking motion to rotational motion, which would in turn drive a generator. A
single Duck was calculated to be capable of generating 6 megawatts (MW) of
electricity—enough to power around 4,000 homes. The plan was to install them in
groups of several dozen.

Initial estimates put the cost of generating electricity in this way at nearly
$1 per kilowatt hour (kWh), far more than nuclear power, the most expensive
electricity at the time. But as Dr Salter and his team improved their design,
they managed to bring the cost-per-kWh down to the cost of nuclear power. Even
so, the research programme was shut down by the British government in 1982. The
reasons for this were not made public, but it is widely believed to have
happened after lobbying by the nuclear industry. In testimony to a House of
Lords committee in 1988, Dr Salter said that an accurate evaluation of the
potential of new energy sources would be possible only when “the control of
renewable energy projects is completely removed from nuclear influences.”
Salter’s Duck never took to the seas, but it sparked interest in the idea of
wave power and eventually helped to inspire other designs. One example is the
Pelamis device, designed by some of Dr Salter’s former students, who now work at
Pelamis Wave Power, a firm based in Scotland. Three such devices, each capable
of generating up to 750kW, have been deployed off the coast of Portugal, and
dozens more are due to be installed by 2009. There are also plans for
installations off Orkney in Scotland and Cornwall in England.

AWS Ocean Energy's submerged buoy; Limpet; Oyster; and Pelamis
As waves travel along the 140-metre length of the snakelike Pelamis, its hinged
joints bend both up and down, and from side to side. This causes hydraulic rams
at the joints to pump hydraulic fluid through turbines, turning generators to
produce electricity. Pelamis generators present only a small cross-section to
incoming waves, and absorb less and less energy as the waves get bigger. This
might seem odd, but most of the time the devices will not be operating in stormy
seas—and when a storm does occur, their survival is more important than their
power output.

Oh buoy

The Aquabuoy, designed by Finavera Renewables of Vancouver, takes a different
approach. (This is the device that Pacific Gas & Electric hopes to deploy off
the California coast.) Each Aquabuoy is a tube, 25-metres long, that floats
vertically in the water and is tethered to the sea floor. Its up-and-down
bobbing motion is used to pressurise water stored in the tube below the surface.
Once the pressure reaches a certain level, the water is released, spinning a
turbine and generating electricity.

The design is deliberately simple, with few moving parts. In theory, at least,
there is very little to go wrong. But a prototype device failed last year when
it sprang a leak and its bilge-pump malfunctioned, causing it to sink just as it
was due to be collected at the end of a trial. Finavera has not released the
results of the trial, which was intended to measure the Aquabuoy’s power output,
among other things. The company has said, however, that Aquabuoy will be
profitable only if each device can generate at least 250kW, and that it has yet
to reach this threshold.

Similar bobbing buoys are also being worked on by AWS Ocean Energy, based in
Scotland, and Ocean Power Technologies, based in Pennington, New Jersey, among
others. The AWS design is unusual because the buoys are entirely submerged; the
Ocean Power device, called the PowerBuoy, is being tested off the coast of Spain
by Iberdrola, a Spanish utility.

The Oyster, a wave-power device from Aquamarine Power, another Scottish firm,
works in an entirely different way. It is an oscillating metal flap, 12 metres
tall and 18 metres wide, installed close to shore. As the waves roll over it,
the flap flexes backwards and forwards. This motion drives pistons that pump
seawater at high pressure through a pipe to a hydroelectric generator. The
generator is onshore, and can be connected to lots of Oyster devices, each of
which is expected to generate up to 600kW. The idea is to make the parts that go
in the sea simple and robust, and to keep the complicated and delicate bits out
of the water. Testing of a prototype off the Orkney coast is due to start this summer.

The logical conclusion of this is to put everything onshore—and that is the idea
behind the Limpet. It is the work of Wavegen, a Scottish firm which is a
subsidiary of Voith Siemens Hydro, a German hydropower firm. A prototype has
been in action on the island of Islay, off the Scottish coast, since 2000. The
Limpet is a chamber that sits on the shoreline. The bottom of the chamber is
open to the sea, and on top is a turbine that always spins in the same
direction, regardless of the direction of the airflow through it.

As waves slam into the shore, water is pushed into the chamber and this in turn
displaces the air, driving it through the turbine. As the water recedes, air is
sucked back into the chamber, driving the same turbine again. The Limpet on
Islay has three chambers which generate an average of 100kW between them, but
larger devices could potentially generate three times this amount, according to
Wavegen. Limpets may be built into harbour breakwaters in Scotland and Spain.
Dozens of wave-energy technologies are being developed around the world: ideas,
in other words, are not what has held the field back. So what has? Tom Thorpe of
Oxford Oceanics, a consultancy, blames several overlapping causes. For a start,
wave energy has lagged behind wind and solar, because the technology is much
younger and still faces some big technical obstacles. “This is a completely new
energy technology, whereas wind and photovoltaics have been around for a long
time—so they have been developed, rather than invented,” says Mr Thorpe.
The British government’s decision to shut its wave-energy research programme,
which had been the world’s biggest during the 1970s, set the field back nearly
two decades. Since Britain is particularly well placed to exploit wave energy
(which is why so many wave-energy companies come from there), its decision not
to pursue the technology affected wave-energy research everywhere, says Mr
Thorpe. “If we couldn’t do it, who could?” he says.

Once interest in wave power revived earlier this decade, practical problems
arose. A recurring problem, ironically enough, is that new devices underestimate
the power of the sea, and are unable to withstand its assault. Installing
wave-energy devices is also expensive; special vessels are needed to tow
equipment out to sea, and it can be difficult to get hold of them. “Vessels that
could potentially do the job are all booked up by companies collecting offshore
oil,” says Trevor Whittaker, an engineer at Queen’s University in Belfast who
has been part of both the Limpet and Oyster projects. “Wave-generator
installation is forced to compete with the high prices the oil industry can pay.”

Another practical problem is the lack of infrastructure to connect wave-energy
generators to the power grid. The cost of establishing this infrastructure makes
small-scale wave-energy generation and testing unfeasible; but large-scale
projects are hugely expensive. One way around this is to build a “Wave Hub”,
like the one due to be installed off the coast of Cornwall in 2010 that will
provide infrastructure to connect up wave-energy arrays for testing.

Expect flotations

But at last there are signs of change. Big utilities are taking the technology
seriously, and are teaming up with wave-energy companies. Venture-capitalists
are piling in too, as they look for new opportunities. Several wave-energy
companies are thought to be planning stockmarket flotations in the coming
months. Indeed, such is investors’ enthusiasm that Mr Thorpe worries that things
might have gone too far. A big failure could tarnish the whole field, just as
its prospects look more promising than ever.

Whether one wave-energy device will dominate, or different devices will suit
different conditions, remains to be seen. But wave energy’s fortunes have
changed. “We have to be prepared for some spectacular failures,” says Mr Thorpe,
“but equally some spectacular successes.”


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