We do not know any successfully commercialised technology converting ocean wave energy into electricity. There is a long list of wave energy projects based on the different designs but none of them could produce commercially valuable power.
Note: we review only ocean wave energy converters. We do not consider designs using tidal or any other form of ocean energy. Also, we do not consider any submerged WEC designs. We do not believe that submerged WEC can produce commercially valuable power. Our concerns:
The cost of any submerged devise in times dearer than cost of the device with the similar power output located above water level. Even when alternator located at shore it does not make the cost of installation less expensive.
The cost of installation and maintenance is much higher.
Ability to interact with waves and absorb energy from large ocean area is limited.
There are 4 main types of floating wave energy converters
- Point absorbers
- Oscillating Water Column (OWC)
A point absorber is a floating structure with components that move relative to each other due to wave action (e.g., a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical or hydraulic energy converters.
Terminator devices extend perpendicular to the direction of wave travel and capture or reflect the power of the wave. These devices are typically onshore or nearshore; however, floating versions have been designed for offshore applications. The oscillating water column (OWC) is a form of terminator in which water enters through a subsurface opening into a chamber with air trapped above it. The wave action causes the captured water column to move up and down like a piston to force the air though an opening connected to a turbine.
The common disadvantage of known designs is unstable output. They interact with wave crest and idle in trough.
Theoretical limit of wave stability approximated by a wave height to wavelength ratio of 1/7
If wave period is 7 seconds, ideal device will work only 1 second and will idle rest of the time. A low efficiency is perfectly embedded into all these designs.
The lack of ability to produce stable continuous output during the wave period is one of the major reasons that makes wave energy projects unsuccessful.
There is only one solution to make wave energy converter to provide continuous output during the wave period is using an array of devices deployed along the wave length. Each unit will work only a second and idle rest of the time. Obviously, this solution has enormous capital and operational expenditures, which makes cost of power completely uncompetitive on electricity market.
An oscillating water column (OWC) is most promising concept for ocean wave energy development, because it does not have any mechanical parts and can be inexpensive in mass production.
What is the main advantage of OWC against the other concepts, such as a float or buoy? Simplicity and reliability. OWC pushes air out and sucks it back and can be considered as a single cylinder air pump where oscillating water inside OWC plays role of piston. To be able to produce continuous output during the wave period a long line of rigidly connected OWC’s has to be deployed.
To be able to synchronise direction of airflow among multiple OWC’s we added inlet and outlet flaps to each OWC.
Two air ducts allow to create unidirectional air flow to feed wind turbine.
We adopted a concept of reciprocating air pump to our design. OWC with inlet and outlet flaps connected to inlet and outlet ducts works like air pump, where OWC’s are cylinders and oscillating water inside OWC is piston. Please, welcome
the Wave Mill!