Ocean Wave Power
Wave power devices extract energy directly
from surface waves or from pressure fluctuations below the surface. Renewable
energy analysts believe there is enough energy in the ocean waves to provide up
to 2 terawatts of electricity. (A terawatt is equal to a trillion watts.)
Wave power can't be harnessed everywhere.
Wave-power rich areas of the world include the western coasts of Scotland,
northern Canada, southern Africa, Australia, and the northeastern and
northwestern coasts of the United States. In the Pacific Northwest alone, it's
feasible that wave energy could produce 40–70 kilowatts (kW) per meter (3.3
feet) of western coastline. The West Coast of the United States is more than a
1,000 miles long.
Technologies
Wave energy can be converted into
electricity through both offshore and onshore systems.
Offshore Systems
Offshore systems are situated in deep
water, typically of more than 40 meters (131 feet). Sophisticated
mechanisms—like the Salter Duck—use the bobbing motion of the waves to power a
pump that creates electricity. Other offshore devices use hoses connected to
floats that ride the waves. The rise and fall of the float stretches and relaxes
the hose, which pressurizes the water, which, in turn, rotates a turbine.
Specially built seagoing vessels can also
capture the energy of offshore waves. These floating platforms create
electricity by funneling waves through internal turbines and then back into the
sea.
Onshore Systems
Built along shorelines, onshore wave power
systems extract the energy in breaking waves. Onshore system technologies
include the following:
-
Oscillating water column
The oscillating water column consists of
a partially submerged concrete or steel structure that has an opening to the
sea below the waterline. It encloses a column of air above a column of water.
As waves enter the air column, they cause the water column to rise and fall.
This alternately compresses and depressurizes the air column. As the wave
retreats, the air is drawn back through the turbine as a result of the reduced
air pressure on the ocean side of the turbine.
-
Tapchan
The tapchan, or tapered channel system,
consists of a tapered channel, which feeds into a reservoir constructed on
cliffs above sea level. The narrowing of the channel causes the waves to
increase in height as they move toward the cliff face. The waves spill over
the walls of the channel into the reservoir and the stored water is then fed
through a turbine.
-
Pendulor device
The pendulor wave-power device consists
of a rectangular box, which is open to the sea at one end. A flap is hinged
over the opening and the action of the waves causes the flap to swing back and
forth. The motion powers a hydraulic pump and a generator.
Environmental and Economic
Challenges
In general, careful site selection is the
key to keeping the environmental impacts of wave power systems to a minimum.
Wave energy system planners can choose sites that preserve scenic shorefronts.
They also can avoid areas where wave energy systems can significantly alter flow
patterns of sediment on the ocean floor.
Economically, wave power systems have a
hard time competing with traditional power sources. However, the costs to
produce wave energy are coming down. Some European experts predict that wave
power devices will find lucrative niche markets. Once built, they have low
operation and maintenance costs because the fuel they use—seawater—is free.
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