The patented SurfWEC variable-depth platform (US Patent 8093736 B2 enabling the Shoaling Feature and Storm Load Avoidance Feature) is applicable to other generic WEC concepts including flapper/surge devices. Economic analysis of traditional bottom-mounted flapper/surge devices drives the existing designs into the boutique power generation realm rather than the sustainable energy triad. This is a shame because many people have worked very hard for many years to make headway on WEC technology development.
One effort we like is the Resolute Marine Wave2O design. Here is an image from their website:
This WEC uses a flapper to harvest waves, and from an engineer’s point of view it has some interesting features. It is mechanically tough, there has been some prototype development, and it appears that soon there will be a deployment of a system for desalination of seawater to produce drinking water.
However, this approach suffers from a few issues that makes it difficult to cost effectively produce utility level energy:
It is sensitive to changes in water depth (in significant tidal ranges it will not be optimally deployed)
When sized for large waves it will not effectively respond to small waves
It is unidirectional; when waves run parallel to the flapper the unit will not generate much energy.
It has no storm avoidance feature beyond flooding the flapper parallel to the sea bottom, but then it becomes a very complex sizing issue. (A small flapper for small waves cannot sit in deep water where the flapper can be flooded to be protected from huge waves)
But once a device like this is mounted on a SurfWEC base, things become much more economically interesting.
Assume that a large bottom-mounted unit can produce 1000 megawatt-hours (1000 MWh) per year.
If the unit can be turned to take advantage of optimal wave directions it could double its energy output (this is low since perfect alignment is rare in a fixed unit and it will be 100% in a unit that can rotate) so now the output is 2,000 MWh per year.
Then if the SurfWEC base can place the device in optimal wave height it can probably double its energy output once again. So now the output is 4,000 MWh per year.
Then if the unit can be optimized to always operate in surging waves it can probably double its energy output once again. So now the output is 8,000 MWh per year. (As engineers it is very rare to encounter an efficiency increase that is progressive like this, often one increased efficiency can be added to another, but it is very rare where efficiency increases can be multiplied).
Then if the unit can keep producing in truly heavy weather by running in submerged operation, it will probably add a few more percent in output.
As such, it is not unreasonable to expect that a unit deployed on a SurfWEC variable-depth platform will produce 8 times as much energy per year as a fixed ocean bottom mounted unit.
Undoubtedly a unit on a SurfWEC variable-depth platform is more expensive, but if one were to assume it will be twice as expensive, the cost to produce energy is a quarter of a fixed unit and that is a huge gain that can drive WEC into the utility cost realm.
Hydrodynamically mounting a flapper on a SurfWEC base is more complex than using a bobber to achieve resonance, but that is an optimization exercise and there are solutions to that issue such as providing an opening between the flapper and the base and to carefully design the level of buoyancy in the flappers.
Meanwhile, we have made an animation to further describe the approach.
If a new technology is not linked to a single approach or application, a technology inherently becomes more rugged. SurfWEC is rugged technology.