Combined breakwater and wave power generator


(George busby) #21

A wave loses energy when it enters shallow water because of friction with the sea floor. If the sea floor is uneven or has vegetation such as mangrove swamp the energy loss through friction will be greater
In deep water little energy is lost to friction and hence waves can cross oceans. They will decrease in size as they spread out.
At any spot the waves that it receives will be a combination of waves that were generated at different places and have interacted. Hence, waves can be very variable from one to the next.


#22

Yet, transferring energy from the surface creates a higher velocity at another depth, just like a restriction in a pipeline. This higher velocity could potentially be used more effectively to drive an underwater turbine…


#23

I’m not sure we are communicating clearly, @Georgeb.

A surface wave is a specific type of wave that exhibits specific properties. It has an amplitude that equals only 1/2 the distance from crest to trough …

… and, therefore, the water just below the trough is, for all practical purposes related to seasteading, undisturbed by the surface wave.

ALL issues on the open sea, related to that energy, happen between the crest and the trough. Unless one plans to locate a seastead in the shallow water of a coastal area, discussions of friction and surf are irrelevant.

Further, the energy of the surface wave - on the open sea - doesn’t dissipate by friction or spreading out. The surface wave travels in a directional line and changes direction by refraction. This is how traditional Polynesian sailors navigate … by knowing the locations of islands and the directions of surface waves created by the prevailing winds, and calculating their location relative to the surface waves that are refracted from those islands.

The surface wave dissipates by lifting water, forming the swells, as it travels across the open water. Formed by surface winds, the surface wave is either reinforced/maintained by more wind OR it dissipates by fighting against gravity as it lifts water into swells.

On the open sea, any proposed “breakwater” would be a floating breakwater … which is any oxymoron.

So your proposal - of lifting water into storage tanks - must deal with only that narrow depth of water contained within the range (2 x amplitude) of the surface wave. Below that range (i.e., below the trough) there is virtually no convertible surface wave “energy”.

This comment thread is a conflation of two basic concepts - surface waves and breakwaters - that must be dealt with differently on the open sea, as compared to a place (shallow water or shoreline) where a breakwater will work because it can be physically connected to land.

Other threads have, in the past, conflated “breakwater” with efforts to deal with the problems of surface waves on the open sea … and those are DIFFERENT problems requiring different solutions.

Breakwater deals with mass … what to do about surface waves on the open sea is strictly an energy problem.

Consequently, on the open sea, creating electricity from any form of surface wave capture is really just a matter of deciding which project has the best cost-to-build-and-maintain ratio as compared to electrical production.

The conclusion MIGHT be another form of energy production (solar, nuclear, etc.) or it might be your plan.

And kudos to you, George, for thinking of ways to create a potential solution.

My purpose is not to criticize your plan, but to point out that this comment thread was using similar words to mean different things and conflating a near-shore issue with an open-sea issue.

Your ‘vertical storage’ idea has some merit - and alternative applications, btw - so I wasn’t trying to discourage your brainstorming.

But this (TSI) forum has traditionally mixed up vocabulary and meaning within the same comment threads, leading to confusion. I was trying to point out that this thread had taken a similar turn.

Regards, and thanks for “floating” your idea for everyone to consider. :slight_smile:


#24

Alternative use of ‘vertical storage’ -

Water towers - common in small towns in the US - serve a valuable purpose we often overlook …

… in that, if electrical power is lost, the community still has positive water pressure for several purposes (drinking water, waste treatment, firefighting, and - potentially - desalination).

A seastead (of any size) that is surrounded by water still needs to maintain positive water pressure … and vertical storage is the best guarantee of maintaining that fail-safe capacity.

So … regardless of the conclusion about energy production, a discussion about lifting and storing water is a valuable mental exercise.


#25

As a suggestion (food for thought) -

The metric system was designed to directly convert volume to weight, and most of the world already uses metric measurements.

So, in a displacement calculation, a 45,000 cubic cm box floats 45 kilograms.

Since seasteading inherently deals with the displacement of ocean water …

… we might consider adopting metric measurements as a seasteading standard.


#26

Compromise approach…
Use a backflow preventer and well pressure reservoirs basing capacity on occupancy of each flat. Maybe 50 gallons per person? That distributes the emergency water supply, w/o needing one massive tank or tower.

Basically a community main line supplies r-o water, each flat has its own backup water supply.

However, any gravity based storage will require too much central structure, otherwise. Storing water as an energy backup is going to require more capacity than reasonably attainable.

Think, what is the output of, say the Hoover dam? How much water storage? How are you going to float that much water, high enough, to provide that backup capacity?


#27

Are you suggesting that the function performed by breakwaters near the coast (i.e. calming the surface waters) is not necessary on the open ocean?


#28

No …

… because “the function performed by breakwaters” erected along coastlines and around ports is to protect land from erosion, channels from infil, and docks from excessively choppy moorings.

“Calming the surface waters” might be a byproduct, but that is NOT the function of breakwaters. Calming the surface waters for ocean-going vessels is needless … precisely because they are ocean-going vessels.

That is not to say that artificial barriers are never created to “calm surface waters”. San Diego’s Mission Bay is an example of a saltwater playground that has utilized artificial barriers (fill dirt and rocks, and sand) to create “calm surface waters”. But those places exist only where a breakwater or jetty (or natural terrain) has already dampened the effects of ocean currents and surface waves.

ON THE OPEN OCEAN… there is no need to worry about mass, because the only concern for a seastead is dealing with swells caused by surface waves. Dealing with MASS on the open ocean is called “displacement”.

So … although a seastead does want to create calm surface waters around the seastead …

… the problem for the seastead is undesired energy, not undesired mass.


#29

@JL_Frusha -

One might consider the idea of vertical storage impractical, but there is nothing better on Earth for emergency capacity than a gravity-powered system. When everything else fails, gravity remains.

Beauty is in the eye of the beholder.

So is design preference.

I’m not arguing that vertical storage is the best way for anything, but it IS a practical alternative for some potential scenarios.

As such, we should not (in my opinion) oppose the development of the concepts when they are other people’s ideas funded by their own bank account.

And … in truth … the mental exercise of turning horizontal (surface wave) energy into a vertical pump feeding a storage tank that requires ‘X’ displacement would yield data that someone somewhere might find useful.

I object to those who claim their idea is the only option, when clearly other ideas are also viable.

But, if somebody wants to brainstorm an idea and commit their own resources to their experiment, I’d prefer to see how that works out. Maybe part of their data might be helpful to another person’s project.

I’m not convinced that this form of energy production is the best alternative, so I’ll invest my own funds in some beer recipes. :stuck_out_tongue_closed_eyes:

But … hey … if this scheme turns into a free source of energy, I’ll happily admit my error … as I rush to buy more electrical equipment and expand my (soon to be automated) brewery’s production line. :wink:


(George busby) #30

If you are thinking of building floating cities in deep water you will need a floating breakwater. You need a breakwater not only to calm the seas but to stop the islands being pushed about and to stop water flooding onto the land.
In deep water waves are bigger than on shallow water because there is less energy loss to friction. They could generate more electricity.
If floating reservoirs were used as breakwaters they would need two sets of floats: one set to support the empty reservoir and another set to support the weight of water in the reservoir…
If half the capacity of the reservoir was used by floats a 2m rise in water level in the reservoir would cause it to sink by 1m and give a net head above sea level of 1m.
The beauty of water pressure is that it is the same in all directions and so pressure applied horizontally by a wave can be converted to vertical pressure in the reservoir.


#31

No. Breakwaters deal with mass, and swells are merely manifestations of surface waves.

A different thing entirely.

But … hey … if you keep repeating the mantra long enough, physics might change over to your version of reality.

Good luck.


#32

If someone would, please show an example of this hypothetical system. I think the words are beginning to make sSisyphus task look easy. I fail to see how floating a large lake, on the ocean, simply as mass water storage for turbines or any other power generator type sounds totally absurd. This one, I’m gonna need to see an example of.


#33

All of the seastead models that I have seen show a breakwater around the complex. Are you saying that it’s not needed? Or are you saying that “breakwater” is the wrong word for what’s needed?


#34

For practical purposes, perhaps the Wave Dragon is close to your theoretical floating water storing idea.

So far, the project has shown promise, but it’s not going to scale feasibly to store a reasonable 3-5 day supply of water for the turbines.

The hurdle they have also failed to overcome is storm breakage and cost to manufacture vs return of investment. Try finding someone willing to invest millions on a 50 year payback…

Executive Summary
Wave energy is a renewable energy resource that harnesses the power of the waves on a body of water
through oscillatory motion or through a hydrokinetic turbine. Although wave energy is not currently an
economically viable source of power, in the future wave energy will contribute to the production of a
substantial amount of the world’s power needs. Through the implementation of this case study, in which a
wave energy converter is modeled and optimized, power and cost values of wave energy were found, which
contributed to the creation of a wave energy roadmap. In the case study, it was found that cost of energy
for the design and power output from the overtopping device were 1.72 $
𝑘𝑊ℎ
and 520 W, respectively. It
was found that both of these values are insufficient for economic feasibility. However, sources of the
elevated costs can be analyzed in the road map section to determine what it would take to overcome these
barriers.
The wave energy roadmap describes the timeline as well as some of the barriers that need to be overcome
for wave energy become economically viable. It was found that through historical trends in other renewable
energy systems, combined with projections of these systems, coal, and wave energy, that wave energy
would become economically feasible around the year 2052. Further research conducted found that many
barriers need to be overcome for wave energy to become viable such as improved government policy,
funding, and further research in the areas of wave energy conversion techniques and ocean mapping.


(George busby) #35

I am very familiar with the wave dragon which also uses small reservoirs and potential energy to generate electricity. The problem with the wave dragon is that water enters the reservoir by overtopping. Only the part of the wave with enough energy to climb the ramp enters the reservoir. It then drops into the reservoir and so loses some potential energy. If the reservoirs are shallow to reduce this energy loss there is energy loss from overflowing the reservoir. If the reservoirs are deep there is greater loss of potential energy. There is also energy losses to friction as water climbs the ramp. The ramp also has to absorb some of th


(George busby) #36

The ramp also has to absorb some of the kinetic energy of the wave and so there is a danger the whole structure will get pushed about, which has happened in practice.
I propose that water enters the reservoir through one way openings in its sides. Water will enter if the pressure from the incoming wave is greater than the pressure inside the reservoir. There is no loss of potential energy from dropping into the reservoir or friction losses on the ramp. The kinetic energy of waves is mainly absorbed by water in the reservoir and so there is less risk of the structure being pushed about…
The wave dragon is not designed as an energy storage device and in my view it is too inefficient to be economic.


(George busby) #37

Breakwaters deal with energy rather than mass. They need to be high enough to avoid overtopping and be able to deal with the kinetic energy of waves.
We want to stop water flooding onto land whether caused by waves wth potential energy overtopping or water being pushed onshore by the kinetic energy of the wave. We also need calm waters to avoid damaging boats when docking and for safety reasons.
Swells are just waves that have travelled long distances.


#38

OK, so, something like a giant pool skimmer, except some way to also push water up into a Wave Dragon reservoir…

First your hinges are continually moving, and doors are either being bashed, or opening to admit water.

Second, you have to screen it, to keep flotsom and jetsome, as well as live creatures out.

Third, it still has to be more durable than Wave Dragon

Fourth, it needs to store enough water to have a reserve capacity, during lulls.

Fifth, it needs to be moored in much deeper water.

Not saying it cannot be done, mind you, just trying to point out what I see as immediate problems.


(George busby) #39

The doors will be opening and closing every few seconds but the pressure on them is the net difference between the pressure inside the reservoir and the pressure exerted by the incoming wave. As the reservoir fills up this pressure difference will reduce and the doors will close slowly rather than be bashed about.
Screening for floating objects would probably be necessary but fish should be able to pass through the turbines. If objects do stop the doors closing they should be moved by the next wave.
Durability is of course vital and would need to be carefully considered.
The reservoirs themselves provide the storage capacity and the bigger the reservoirs the greater the storage capacity. Waves are usually continuous with completely flat seas fairly rare. The storage capacity of the reservoirs is most useful in capturing the energy of heavy seas which in most wave power devices is wasted. The energy stored also helps to smooth electricity output and enables maximum electricity production at times of peak demand.
In shallow water the reservoirs can be fixed to piles so that the bottom of the reservoirs is at sea level. In deep water the reservoirs can be supported by floats.
As water is able to flow under the reservoirs the problem of stagnant water associated with conventional breakwaters is avoided.


#40

“Breakwater” is both the wrong word and the wrong concept.

But minimizing or eliminating the swells caused by surface waves (the energy) is absolutely necessary for a seasteading community.