A demonstration
of a novel technology that uses the kinetic energy of ocean
waves to generate electricity is scheduled for deployment
off the California coast by fall. Similar in concept to pumped-storage
hydropower designs, it protects sensitive electrical equipment
from corrosive seawater by locating turbines, circuitry and
transmission cables on land.
Under the patented "Seadog"
system, a buoy riding the up-and-down motion of waves drives
an attached piston (click
here to view illustration). The piston draws in seawater,
then expels it into a 24-in.-dia buried pipeline running to
the shore. The pressure build-up continuously pushes the water
up a coastal bluff into a reservoir. From there, it is discharged
through an off-the-shelf hydroelectric turbine to generate
electricity before the salt water is returned to the ocean.
A single demonstration pump not
connected to an onshore reservoir will be deployed off Humboldt
County, Calif., by November. The buoyancy block will float
inside a cage of piles driven into the sea floor and extending
about 35 ft above mean high water, allowing sea swells of
10 to 12 ft to drive the pump.
"Permitting will take a long
time," frets Roger Bedard, proposal manager at the Electric
Power Research Institute, Palo Alto, Calif. He says the technology
owner and project developer, Independent Natural Resources
Inc., Eden Prairie, Minn., may experience a longer delay from
permitting than it is prepared to accept. But INRI Vice President
Doug Sandberg says he is hoping for a permit waiver for the
demonstration, which "is no more invasive than putting
in a buoy." If the demonstration is successful, a 16-pump
array with onshore facilities would follow. Sandberg expects
permitting to take 12 to 24 months. A contractor has not yet
been selected, but firms "are standing in line,"
he says.
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The land-based portion "is,
in effect, a mini-hydroelectric project," says Chris
Guay, an oceanographer at the Lawrence Berkeley National Laboratory
and consultant to INRI. The hybrid design allows the project
to sidestep the intermittency challenges of renewable power
because electricity can be generated on demand rather than
subject to the whims of nature, says Guay.
The company recently tested a 1Ú32-scale
prototype at the Offshore Technology Research Center at Texas
A&M University, College Station. Sandberg says the performance
validated laboratory predictions. With its 65-in.-dia buoyancy
block and a 4-in.-dia piston-head, the prototype created "1,200
lb of lift that translated into a maximum of 187 psi. For
every one psi, we could move water 2.33 ft," he says.
The company now intends to scale
up the pump to full size in a marine setting. The test will
identify any mitigation needed for environmental impact, such
as small marine life entering the piston cylinder. INRI also
hopes to show that the Seadog technology can be used to pump
feedwater into desalination plants.
With a nameplate generating capacity
of 750 kW, the wave farm would be located just beyond the
breaker point–a distance of up to one mile from shore.
The site depends on the configuration of the continental shelf
and the onshore reservoir needs a minimum elevation of 150
ft. "We have estimated that we can be in anywhere from
50 to 200 ft of water," says Sandberg. He estimates a
total project cost, including permitting, of roughly $3 million.
