wave energy systems
Wave energy is rapidly emerging as one of the best means of
harnessing energy from the ocean. There are three kinds of
approaches which have been used to harness wave energy. Let's review these:
1. Buoys or Floats - Floating buoys have
been developed which can generate energy from the bobbing or pitching
motion caused by the waves. In some buoy type systems the buoy
uses a simple mechanical system to turn a crankshaft. For example, in
the Indian I-wave system the wave action raises the heavy partially buoyant piston that drives the overhead crankshaft by half turn. The receding wave drops the piston completing the balance half turn. One revolution is obtained for every wave. Using
a gear box and a generator the current is produced continuously.
Vertical buoys can also be used in a similar manner to move a piston up and down which contains a permanent magnet. The magnet is surrounded by a copper wire coil. As the magnet moves back and forth through the coil an electric current is automatically generated. One of the advantages of this approach is that the current is produced directly without
the need of a generator.
The buoy approach can be used with both
vertical and horizontal types of buoys. An example of a horizontal
buoy is the Pelamis wave energy converter which uses semi-submerged cylinders
linked by hinged joints. It looks a lot like a sea serpent in
the water and so was named after the Pelamis sea snake. Inside
each cylinder there is a hydraulic ram which pumps high-pressure oil
through hydraulic motors. The hydraulic motors in turn
drive electrical generators inside the cylinder. Many of these
cylinders can be combined and then the energy can be fed to an
underground sea cable and back to shore.
2. Oscilating Water Columns - Another approach to generating
energy is to use a water filled column in which the rise and fall of
the water in the column moves air or fluid which in turn spins an electrical
generator mounted at the top of the column. The Aquabuoy
system recently developed
by the Finnish company Finavera Renewables is an example of this type
3. Focusing Devices - A third approach is to use channels
near the shore to the wave energy into an elevated reservoir.
Then as the water flows back out of the reservoir a standard
hydroelectric water turbine is used to generate electricity.
There were a number of projects in the 1970's which tried to use this
approach but they ran into both funding and technical problems.
These early projects underestimated the amount of damage that could be
done to the system by storms and salt corrosion.
Pros and Cons of Wave Energy Generation
Pros - Water by its very nature is capable of transferring a
great deal of kinetic energy as compared to wind energy systems.
Consequently even small wave energy devices are capable of producing a
great deal of energy. Also, wave energy devices are usually low
profile and so do not provide much of a visual distraction if placed
off-shore. A big advantage of wave energy is simply its potential.
Our planet is mostly ocean and so the capacity for waves as a
renewable energy source is enormous.
Cons - As with all renewable energy technologies, wave
energy has its share of challenges. Initial attempts at using
wave technology often failed because ocean environments are inherently
changeable. Storms can quickly cause waves to go from a couple
of feet to 40 or 50 feet in a matter of hours. Consequently any
wave energy device must be made incredibly durable in order to survive
harsh ocean conditions. Another major drawback of wave energy
systems is that they are either in the ocean or offshore which means
that any electricity which is generated must be transferred, usually
via undersea cable back to land where it can be used. The laying
and maintenance of the electric cables can add significantly to both
initial costs and maintenance costs.
Several new wave energy projects are moving from the drawing board
into reality in the next few years and so we may soon get a good
picture of how practical this approach to renewable energy is. The Federal Energy Regulatory Commission (FERC)
recently issued a license for a hydrokinetic energy project, which will be located in
Makah Bay off the coast of Washington State. Scotland is moving
ahead with a full-scale prototype of the Pelamis tidal device
beginning in 2008, with final installation during 2009. Portugal
is also planning to implement a Pelamis type of system but has not
finalized a date for implementation. Keep an eye on this
technology. There is definitely more to come!