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 of approach. 

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.

Prospects

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!