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 Dear EarthTalk: Alternative energy sources like wind power, hydrogen and biofuels are getting a lot of headlines these days, but what about efforts to generate electricity from the ocean's waves? ---- Tina Cook, Naples, FL
The concept is simple, says John Lienhard, a University of Houston mechanical engineering professor:
"Every day the moon's gravitational pull lifts countless tons of water up into, say, the East River or the
Bay of Fundy. When that water flows back out to sea, its energy dissipates and, if we don't use it, it's simply
spent." According to Energy Quest, an educational website of the California Energy Commission, the sea can
be harnessed for energy in three basic ways: using wave power, using tidal power, and using ocean water
temperature variations in a process called Ňocean thermal energy conversion" (OTEC).
In harnessing wave power, the back-and-forth or up-and-down movement of waves can be harnessed, for
example, to force air in and out of a chamber to drive a piston or spin a turbine that can power a generator.
Some systems in operation now power small lighthouses and warning buoys. Harnessing tidal energy, on the
other hand, involves trapping water at high tide and then harnesses its energy as it rushes out and drops in
its change to low tide. This is similar to the way water makes hydroelectric dams work. Already some large
installations in Canada and France generate enough electricity to power thousands of homes.
An OTEC system uses temperature differences between deep and surface waters to extract energy from the
flow of heat between the two. An experimental station in Hawaii hopes to develop the technology and someday
produce large amounts of electricity on par with the cost of conventional power technologies.
Proponents say that ocean energy is preferable to wind because tides are constant and predictable and
that water's natural density requires fewer turbines than are needed to produce the same amount of
wind power. Given the difficulty and cost of building tidal arrays at sea and getting the energy back
to land, however, ocean technologies are still young and mostly experimental. But as the industry
matures, costs will drop and some analysts think the ocean could power nearly two percent of U.S.
energy needs.
Several companies now work at the cutting edge of ocean power technology. Scotland's Ocean Power
Delivery Ltd. has a wave system called Pelamis that it hopes to install in waters off of California's
wave-battered central coast. And Seattle, Washington's Aqua Energy has installations off the coasts
of Oregon, Washington and British Columbia and is in talks with utilities about providing the
Pacific Northwest with hundreds of megawatts of ocean energy within the next decade.
Tidal energy pioneers are also hard at work on the U.S. Atlantic coast. The New Hampshire Tidal
Energy Company is developing tidal power in the Piscataqua River between New Hampshire and
Maine. And a company called Verdant Power is providing Long Island City, New York with
electricity through tidal river turbines and has begun installation of tidal power systems in
New York City's East River.
CONTACTS: Ocean Power Delivery Ltd., www.oceanpd.com;
Aqua Energy (Finavera Renewables),
www.verdantpower.com.
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Previous Earthtalk questions:  |
As any board or body surfer will tell you, the ocean's tidal currents pack considerable wallop. So why wouldn't it
make sense to harness all that formidable power, which is not too unlike that of the rivers that drive hydropower
dams or the wind that drives wind turbines, to make energy?