Illustration courtesy Theoretical and Applied
Fluid Dynamics Laboratory at the University of California
Off the southern coast of Australia, a new
effort is under way to capture the energy embedded in ocean swells.
Special buoys will be used to convert the sea's waves into a maximum of
62.5 megawatts (MW), or enough to power 10,000 homes, according to an
announcement this week from project partners Lockheed Martin and Victorian Wave
Partners Ltd. Touted as the world's largest wave energy project, the Australia
buoys are still just a drop in the bucket for wave power potential.
The constantly churning oceans that cover most of the Earth offer an
inexhaustible source of clean energy. The amount of recoverable energy embedded
along the continental shelf of the United States, for example, amounts to
almost a third of all the electricity the country uses in one year, according
to estimates from the Electric Power Research Institute,
"It's emission-free power and it's located close to where most of the
population lives," said Sean O'Neill, president of the Gaithersburg,
M-based Ocean Renewable Energy Coalition (OREC).
But the process of harnessing all of that energy, still in its infancy,
isn't an easy one. "At this stage, putting equipment in the sea and
getting it to work reliably, consistently, during severe storms, is a huge
challenge," said Aquamarine Power CEO Martin McAdam. "If anyone tells
you otherwise, they haven't done it yet." (See related pictures: "Immense,
Elusive Energy in the Forces of Nature.")
Precisely how such a feat could take shape is an open question still to be
answered, in the most literal sense: What designs and mechanisms will work
best? Beyond "PowerBuoys" in Australia, wave energy proponents are
now testing diverse and intriguing ideas for power generators that can even
pull double duty for desalination, maritime surveillance, and other exciting
applications.
A serpentine power-generation device from Pelamis is set to be deployed in
the United Kingdom and Portugal.
PHOTOGRAPH BY DAVID CHESKIN, PA WIRE/AP
Slithering Scottish "Sea Snakes"
Scotland-based Pelamis Wave Power produces an offshore wave energy
converter that looks like a colorful sea snake—and is in fact named for the
species Pelamis platurus. But this snake's bite lies in its ability to produce
power. (See related pictures: "Nature Yields New Ideas for Energy and
Efficiency.")
Anchored 1.25 to 6.2 miles (2 to 10 kilometers) from shore, the Pelamis can
naturally spin on a chain to face wave direction like a flag changes
orientation on a flagpole. Five floating tube sections are linked by universal
joints that flex in two different directions as waves roll down the machine's
serpentine length. Each joint houses cylinders that resist the wave-driven
movements and pump hydraulic fluid to power onboard generators, sending
electricity to shore via underwater cables. The Pelamis can handle dangerous
storm swells much like a surfer paddling out to a favorite break: When big
waves roll in, it simply passes through and under them.
Pelamis has produced six full-scale machines so far, each rated at 750 kW.
Over the past 15 years they have logged more than 10,000 hours at sea while
connected to real electrical grids, notably at the European Marine Energy
Centre (EMEC), off the west coast of the Orkney mainland.
The company plans to debut its technology commercially with Farr Point Wave
Farm, a ten-machine project off the Sutherland coast that is set to produce
power by 2017. Pelamis has several other plans currently on the drawing board.
The UK energy supplier E. ON and ScottishPower Renewables each own a
Pelamis machine currently in sea testing at the EMEC. Each company has
ambitions to develop a wave farm, E.ON's in waters north of EMEC and Scottish
Power Renewables' off Marwick Head in Orkney. These operations could link as
many as 66 machines each and produce 50MW of power at each location. Pelamis
has also partnered with Vattenfall to develop a 10MW wave farm, using up to 14
machines, off the Shetland Islands and is planning another 10MW facility off
the west coast of Lewis in the Outer Hebrides. And in Aguçadoura, Portugal,
past site of a three-machine Pelamis farm, Companhia da Energia Oceânica SA (CEO)
might install as many as 26 machines with a target capacity of 20MW.
Pelamis is one of five competitors vying for the £10 million ($16.6
million) Saltire Prize, offered by the government of Scotland to the first
company able to create a viable green energy system that taps the energy
constantly churning offshore. (Terry Garcia, National Geographic executive vice
president for mission programs, chairs the Saltire Prize committee.) Scotland
has some of the world's most promising wave and tidal energy resources and has
led the way in promoting their development. (Related: Ocean Energy
Teams Compete for $16 Million Scotland Prize.)
Seafloor "Magic Carpet" For Power,
Desalination, and Coastal Protection
Reza Alam, a UC Berkeley engineer and expert at wave mechanics, has created
a power-producing "magic carpet" that serves as an artificial ocean
bottom with multiple applications.
"Mud is known to very strongly dampen ocean waves. Within a distance
of a couple of hundred yards even very strong waves can be completely dampened
out," he said. "So we were inspired to wonder if a synthetic carpet
could respond similarly to the action of waves and absorb that same amount of
energy."
The device features a thin rubber or elastic composite carpet stretched
across across a grid of cylinders and double-action piston pumps. The carpet
adopts the up and down wave motion of its waters and subsequently moves the
attached piston pumps to produce hydraulic pressure with multiple applications.
"The first idea was desalination, near the device or onshore, because
high-pressure water is something we need for that," Alam explained. The
system can also be customized to deliver compressed air, rather than water, for
offshore aquaculture, where it could be used to move cages and oxygenate water.
And of course the system could generate electricity—perhaps in surprising
quantities. In recent wave tank tests, it absorbed more than 90 percent of
incoming wave energy. With that kind of results, Alam estimated, a single
square meter (11 square feet) of carpet system on a seafloor could power a pair
of U.S. homes. A 100-square-meter (1,076-square-foot) patch on the California
coast would equal the power production of a 6,400-square-meter
(68,889-square-foot) solar panel array.
The ocean wave energy converter is meant to be set in 60 feet (18 meters)
of water, where it's protected from storm damage by the water column above and
would be largely invisible to those on shore. It must be carefully sited to
avoid sensitive areas for marine life, like reefs, as well as recreational areas
like surf breaks. But because the system greatly reduces wave impacts by
absorbing their energy, it could also be strategically deployed to create
"safe zones" near coastlines, protecting harbors or slowing erosion.
"The idea first was producing power," Alam explained, "but when
we presented it in conferences, the feedback I got was that protecting harbors
was probably a more immediate application of this idea. Then you don't even
need a pump, just the material to absorb the energy of the waves."
The carpet is currently undergoing wave tank tests and should move to open
ocean trials by 2016, Alam said.
Specially designed buoys can use the rise and fall of ocean waves to
generate energy.
PHOTOGRAPH BY PR NEWSWIRE/LOCKHEED MARTIN/AP
Buoys Boost Energy, Thwart Pirates, Perform Sea
Surveillance
The buoys being installed for the large wave energy project off the coast
of Victoria, Australia, might also be able to make the seas safer.
Ocean Power Technologies (OPT) PowerBuoys are anchored to the ocean floor
but move freely up and down with the ocean swells, driving an onboard
piston-like structure to power a generator and produce electricity sent to
shore via subsea cable. They boast sensors that monitor their own performance
and the ocean's movement, able to switch off power production when waves are
too large and strong.
The buoys may avoid one challenge that offshore wind turbines have faced:
At 38 feet (11.5 meters) high, the buoys present a far lower profile than
offshore wind turbines, which can tower more than 440 feet (135 meters), and
according to an OPT fact sheet, they are not highly visible at a distance of 3
miles (5 kilometers) from shore. Some offshore wind projects have sparked
opposition because of their potential to disrupt ocean views. (Related: Cape
Wind Deadline: Headwinds for Offshore Turbines.)
The buoys are anchored with a proprietary system to avoid seafloor
ecosystem damage, and could even provide some benefits to marine animals by
serving as an artificial reef, said Charles F. Dunleavy, chief executive
officer of OPT.
In addition to delivering power to the grid, the buoys can power themselves
at a remote location and support a flexible suite of sensors and equipment for
maritime security and monitoring off the grid.
The U.S. Navy's Littoral
Expeditionary Autonomous PowerBuoy (LEAP) program tested a smaller, totally
autonomous version of the PowerBuoy with acoustic sensors, communications
systems and signal processing. The equipment might be deployed someday as
maritime surveillance, protecting sensitive areas or equipment and tracking
illegal ship traffic.
Floating Pumps "Surf" on Wave Energy
Aquamarine Power's Oyster is a simple design, just as its makers intended,
that basically functions as a wave-powered pump. The floating system features a
large, hinged flap anchored in 33 to 50 feet (10 to 15 meters) of water in the
near-shore zone, some .3 miles (.5 kilometers) out. The flap moves with wave
motion, driving attached pistons that push high-pressure water through an
underwater pipeline. That water is funneled to shore, where it powers a
standard hydroelectric turbine—the design keeps complicated moving parts out of
the ocean and on dry land where they can be more easily maintained.
The current Oyster 800 is has been at sea two and a half years—longer than
any other mobile wave energy device. The device's location near the shoreline
and its design are both aimed at mitigating one of wave power's top
challenges-surviving the sometimes brutal conditions in locations like the
Scottish coast.
"Survivability is one thing that we think differentiates Oyster, and
it can really stay out there in big storms," said CEO Martin McAdam.
"It's designed to spill excess wave energy over the top of the machine in
storm conditions, because the machine actually ducks under the water and excess
energy cascades across the back of the wave."
Oyster has withstood several storms with waves of 26 feet (8 meters) and
more. Because of its location in shallow (40 to 50 feet, or 12 to 15 meters)
water, McAdam said the machine shouldn't encounter waves much above 33 feet (10
meters).
The Oyster system is designed for increased scale, so that pipelines could
connect several hundred devices to a single onshore plant producing
electricity. The company, also chasing Scotland's Saltire Prize, has permits
for a 40MW farm off the Isle of Lewis and plans to begin producing power there
within four years.
Underwater Turbines Tap Tidal Power
Waves aren't the ocean's only motion. The gravitational pull of the sun and
moon causes sea levels to rise and fall reliably, typically twice a day. This
horizontal flow of ocean waters offers a regular and predictable energy source
that's being targeted by several companies, including Saltire Prize competitors
MeyGen, ScottishPower Renewables, and West Islay Tidal.
In September of last year, MeyGen was given a permit to install Europe's
biggest tidal turbine array in part of Pentland Firth, the fast-moving channel
between the northeast tip of the Scottish mainland and the island of Stroma (map).
In a recent study, engineers from Oxford and Edinburgh Universities estimated
that underwater turbines in the larger Firth could produce 43 percent of
Scotland's electricity needs—up to 1.9 gigawatts. The MeyGen project would be
the first commercial tidal turbine operation in Scotland.
To tap tidal power, MeyGen is testing seafloor-anchored turbines from two
different manufacturers, Atlantis Resources Corporation and Andritz Hydro
Hammerfest. Unlike their wind-driven counterparts, these would be largely
invisible from above and benefit from the fact that seawater is 832 times more
dense than air. For this reason, a 5-knot ocean current packs more kinetic
energy than a 217 mph (350 km/hr) wind, according to MeyGen statistics.
Other Saltire Prize competitors seek to tap the power of tides.
ScottishPower Renewables, a division of wind energy giant Iberdrola, is
developing (though not yet constructing) a Demonstration Tidal Array in the
Scottish Sound of Islay. Ten Andritz Hydro Hammerfest HS1000 turbines will be
anchored to the seafloor between the islands of Islay and Jura. The test is
preparation for development of a 95 MW tidal energy project at the Ness of
Duncansby, on Pentland Firth waters.
West Islay Tidal is also promoting a project, a 0.8-square-mile
(2-square-kilometer) tidal stream array in 100 feet (30 meters) of water off
the West Islay coast. Here, tides are not only strong but also biodirectional,
meaning that the ebb and flow run conveniently (for turbines) almost 180
degrees opposed to one another. West Islay Tidal hopes to see installation
begin in 2015 and 30 MW capacity complete by the end of 2016
But for all of ocean power's plans and potential, it also poses great
challenges. Systems have to be built to avoid injury to marine mammals and
other ocean life. They have to be robust enough to survive the rough weather
that is common in places with the potential for high ocean energy. Conflicts
can arise between use of the ocean for energy and other activities, such as
fishing, shipping, and recreation. And not least are the financial challenges
of producing energy at competitive rates, and raising investment dollars for
new and relatively unproven technologies.
Like his European counterparts in the field, Sean O'Neill of the OREC
believes all this can be overcome with a vision of clean energy that won't run
out. He also sees a need to speed development of the technology, which will drive
innovations that make it cheaper and better.
"We have polluted the oceans for decades, and here we have a new
use," he said, "so there is some fear of the unknown, and we do need
to make certain of wave and tidal power's impacts and monitor them.
"If there are any negative effects we need to mitigate them, and we'll
probably discover some unintended benefits as well. But most of all, we need to
get these technologies and projects into the water." (See related interactive map: "The Global Electricity Mix.")
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