Combined breakwater and wave power generator

(George busby) #1

The key to building floating cities is to build cost effective breakwaters that also generate electricity and store energy.
The breakwaters consist of reservoirs that convert the kinetic and potential energy of waves into stored potential energy which can then be used to generate electricity.
Water will enter the reservoirs through one way openings in their sides and exit through turbines. Water will enter if the pressure of the incoming wave is greater than the water pressure inside the reservoir and so a head of water above sea level is created.
The reservoirs would be secured to piles and would block the forward motion of waves. The bigger the reservoirs the lower the risk of overflowing in heavy seas.
The reservoirs are able to survive the destructive forces of heavy seas because they are an open structure and the forces are absorbed by water in the reservoirs.


You realize you’re talking about billions, maybe trillions of dollars worth of engineering and materials?

(George busby) #3

The cost of building the reservoirs would probably be similar to the cost of building ship hulls. The reservoirs keep water in and ships hulls keep water out and they both have to cope with similar pressures.
The cost of the turbines should be recouped from the electricity generated.
The total costs would be millions but certainly not billions or trillions.

(Mariusz) #4

I don’t see why this project could not be scaled down and tested on even a small platform. Of course it would not generate megawatts of power, but the general idea could be tested and refined.


The problem is mass. You cannot store elevated volumes of water w/o displacing water. Your water tower, when full, will weigh how many gigatons,to store megawatts of energy?

(George busby) #6

The size of the head of water will vary with the size of the incoming waves and the amount of water used by the turbines. Assuming a working head of 4m, a power of 1Mw would require about 25 tonnes of water to pass through the turbines per second.
A reservoir of size 1000m width by 25m depth by 10m high would store about 250,000 tonnes of water with potential energy of about 12.5 GJ.
Water is heavy and so the structure is very stable and spread over many piles.

(George busby) #7

Using a modified container would be a good start.


Your numbers give ~2.77 hours of backup, based on your consumption estimate.

Piles? How far to bedrock? How deep is the water? Where is the billions coming from for those piles, the containment, turbines, regulating systems, power transmission and distribution?

(George busby) #9

When you compare the costs of building the reservoirs and piles with building conventional breakwaters from the sea floor upwards then I am sure reservoirs would be cheaper to build in deeper water. They have the added advantage that they can produce electricity to offset some of the costs.
Of course the deeper the water the longer the piles and greater the costs. In deep water the reservoirs could be supported by floats instead and they would need to be bigger as they would partially submerge as they fill up.
The reservoirs will help with intraday energy storage and help to maximise output in line with peak demand.
The larger the reservoirs the more energy that can be captured from big waves as well as greater energy storage.
I agree that as a stand alone wave power generator the economics are questionable but if used in addition as a breakwater the economics are much more favourable.


There is no magic formula to float tanks full of water, at any such high capacity, is my point.

That 66 MILLION gallons of water has mass. To SUPPORT that mass, you need a physical structure. To FLOAT it, it has to be MUCH more massive.

You’re talking about creating this as if it’s child’s play. Reality does not support your position, any more than Ellmer’ and Matius’ V shaped boomerang ‘city’. The stresses may not even be calculable, when you throw a storm at it.

I am NOT saying there is no way, but storing that much water, as a physical battery, of 2hrs 45min capacity, for a floating city is physically impossible, without Star Trek miracles that real science doesn’t support.

A nuclear reactor is far more realistic. There are dozens, if not hundreds of them, already at work, for far less, in the worlds oceans, thanks to the Navies of the US, Russia and China.

I’ve already outlined a way to create a non-floating breakwater that the science, economics, and physical capability IS available for. Even the theory for making such a structure was fantasy, 20 years ago.

There are cheaper, more effective ways to do it. Since ot depends on modulating the energy in the waves, to ‘charge’ a layer beneath the surface, take it the next step and add underwater turbines, instead. STILL too expensive to get, and maintain those underwater turbines, to currently justify, but far more feasible.

(George busby) #11

A floating city will need a long breakwater which is obviously a big structure. If the costs of the breakwater is offset by producing electricity that would seem to make sense.
A wave has equal amounts of kinetic and potential energy. I propose converting the kinetic energy into additional potential energy for use in generating electricity.
Conventional breakwaters seek to convert the kinetic energy into heat via friction, but this is inefficient because water is a lubricant.
I do not understand how you propose to deal with the kinetic energy by modulating the energy in waves.
It is the kinetic energy of waves and the resulting hydrodynamic pressure that is so destructive.


Follow these…

(George busby) #13

I am afraid it is my turn to be the sceptic. Wave absorbing is not the same as energy absorbing. You can modify the wave but you can’t lose its energy.
I envisage floating cities starting from the coast and expanding seawards so trying to deflect waves underneath them would not be appropriate.
Sea waves vary greatly in size and so a wave absorbing design needs to cope with this great variety.
The wave bridge looks incredibly flimsy and in my view would be destroyed by the first big wave they encounter. I am very sceptical when efficiencies such as up to 94.5% are quoted because the actual number could be as low as 1%.


The principle is observable in nature, as well. There are naturally calm areas that have similar natural features, such as shoals and reefs, that create protected waters.

(Davi W Jr) #15

now oil… on the other hand…


Aside from cleaning up the toxic environmental issue, IMHO, fossil ‘fuel’ should remain where nature put it. Biofuels are more expensive, but can be sustainable.

An advantage to kelp is that it can be a sustainable source of both nutrition, and fuels, while also keepimg it local.


I wasn’t going to go there … but, yeah, oil films tend to calm the waters.

There is actually a valuable lesson in that. :wink:


So … rhetorical question … where does the surface wave (energy) go when the ripples from a rock tossed into a pond get smaller and eventually disappear?

Does the surface wave not “lose its energy”?

Does not that energy get dissipated by opposing the effect of gravity when the water on the surface is lifted up into the ripples (aka, swells on the ocean)?


Perhaps we’re mixing vocabulary within this thread.

The wave on the open sea IS the energy. What we visibly observe on the open ocean as a “wave” is actually a “swell”.

The “wave” to the surfers or beach-goers isn’t what we’re dealing with when discussing the development of seasteading on the ocean surface.

The wave, as a surface wave (meaning the energy, not the visible thing called “the swell”), doesn’t propagate through the air (or solids) …

… so the waveform creates a swell (visible to us as water lifted up - measured in the amplitude of the wave - the “swell”) …

… and gravitation force acting upon the water consequently dissipates (ultimately, over time) the surface wave energy (assuming, of course, that there is not wind present to create more waves).

That is what happens to the pond ripples.

Whether that surface wave encounters a verticle barrier (e.g., the various [incorrectly named] breakwater designs) …

… or a horizontal barrier (e.g., the air or oil on the water or any other floating object) …

… matters not to the surface wave.

If a surface wave encounters a fluid, it propagates THROUGH the fluid and moves onward in the same direction.

If a surface wave encounters a non-fluid, then it refracts off of it in a different direction and/or transfers energy by (verticle or horizontal) displacement of the object.

(Larry G) #20

And fluids of different densities tend to refract and attenuate the wave energy as well- e.g. different temperatures, oil vs water, water vs air, liquifaction of soils…