Ever see one of those shake-flashlights? Moving a magnet through a coil of wire generates current.
Imagine the letter "H" but with multiple vertical bars, like this |-|-|-|-|-|-|-|-|-|. Each vertical bar is a large plastic tube with a coil of wire inside inside of each is a large cylindrical magnet which sloshes back and forth. The tubes are wired together through the horizontal bar. Encapsulate the whole thing inside a plastic raft, and then tether it to the sea floor or a swingset-like overhead structure.
The result is a way to extract electricity from waves that does not involve moving parts. I.E. it's entirely sealed, hence has no problems with salt-water corrosion or wear items.
I'm not sure how much electricity can be generated like this. I tried to do some numbers and got knee-deep in Gauss, flux, and Oersteads very quickly.-- ShawnBob, Apr 08 2010 Illustration of shake flashlight principle: http://express.hows...aker-flashlight.htm [ShawnBob, Apr 09 2010] Permanent Magnet Linear Generator Buoys http://www.peswiki....ear_Generator_BuoysThese wave motion kinetic dynamo devices seem very close to what you have described in concept, particularly the OSU model. (See the first illustration and also the embedded link to PhysOrg.) Each buoy is apparently able to generate 250KW, and can be grouped in farms of 200 buoys. [jurist, Apr 10 2010] Lighted buoy http://www.oceanscience.com/lights.html [bungston, Apr 12 2010] Wave energy http://en.wikipedia.org/wiki/Wave_powertheoreticals of wave energy [metarinka, Apr 12 2010] mhd power from the ocean http://www.sara.com/RAE/ocean_wave.htmlWaves to run MHD to ocean currents. [travbm, Oct 29 2015] Hello. It sounds good to me but i'm just leaving this because i didn't just want to vote for it and not greet you.-- nineteenthly, Apr 08 2010 Maybe make it spin slowly? Either along the horizontal bar or about itself, like a propeller.-- phoenix, Apr 08 2010 Bigsleep:
Great Link! I've read about this before. This actually is filled with hydraulic fluid which is forced back and forth through a turbine.
One advantage I can think of for the magnets again is that fact that nothing rotates: No seals to replace: No wear items. No expensive turbine blades to replace. No hydraulic fluid to leak in the ocean. It seems like a Ockham's razor of a generator.
The coil of wire is indefinite, and perhaps the magnet too, provided that it doesn't eventually wear a groove inside it's tube.
The gravitational potential energy you speak of is simply the wave height converted into kinetic energy.-- ShawnBob, Apr 08 2010 [+] but are waves generally of the same amplitude and frequency ?-- FlyingToaster, Apr 08 2010 Flying Toaster:
I'm not sure. Oddly enough, frequency rather than amplitude seem to affect my calculations more than anything: N waves per hour and that each wave causes the raft to rock back and forth...i.e. that the magnet generates electricity moving in both ways down the coils. The actual wave height seems of little consequence. It doesn't really need huge waveheight, such as other bobbing type generators. Higher frequency smaller waves would paradoxically seem better with this particular device. All it needs is to rock as much as possible.
This leads to an interesting variant: Perhaps add a vertical shaft with a sail-like fin on top to help rock it?-- ShawnBob, Apr 08 2010 well... there's going to be one freq:ampl ratio that will be productive and not require adjustments (ie: just a free-standing, unpowered buoy). Perhaps making the tubes capable of being slanted ? and "upstream" detectors capable of telling it the height/length/duration of the next wave.-- FlyingToaster, Apr 08 2010 My understanding is that the particle motion inside a wave is a circle.-- baconbrain, Apr 08 2010 //are waves generally of the same amplitude and frequency? //
They could easily be so. All you need is one of those wave- makers that they use in big swimming pools. It could be adjusted to give the ideal frequency and amplitude of wave.-- MaxwellBuchanan, Apr 08 2010 Maxwell:
Unfortunately from an energy perspective, every time energy changes forms it is not 100% efficient in conversion. This would mean that anything that makes the waves in the pool would require more energy than the waves themselves. The notion of putting such a raft in the ocean makes sense only because the waves are already there..i.e. the moon and tides make them vs. haveing to use some external energy to make waves to make energy (if that makes sense). It seems to me that there might be something you could do to condition existing waves (as in a wave pool) into optimal waveforms--perhaps with uniform direction if nothing else.-- ShawnBob, Apr 09 2010 I have a question. The magnets move relative to the wire. The wire is fixed so the magnets must move. Does this mean that the magnets must float in order to be driven by the waves?-- DenholmRicshaw, Apr 09 2010 Denholm:
Yes, the magnets move linearly through the center axis of fixed helical coils within the raft. The entire encapsulated raft floats. The raft is sealed up and the only thing coming out of it is the wire necessary to conduct the electicity it makes. This is the huge advantage because barnacles can grow on it, seagulls can poop on it etc..and nothing really gets damaged because no moving parts are exposed to the environment or the salt-water. Almost no maintenance once it's out there.
Think of your emergency shake-powered flashlight that you buy. --SEE 2nd LINK ABOVE--Throw it in the ocean so that the waves shake it instead of you. Upsize it as large as possible (because the flashlight only outputs a tiny voltage to drive the LED). Perhaps the coils are quite long and there are multiples of them in a single raft...perhaps even more than one magnet sliding through a given coil--whatever geometry maximizes the power output.-- ShawnBob, Apr 09 2010 Are the coils horizontal or vertical?-- DenholmRicshaw, Apr 09 2010 //Unfortunately from an energy perspective//
Awww, shucks. Perhaps the wave generator could be powered by a wind turbine, with the surplus energy being used to drive a large fan which ensures that wind energy is continuously available.-- MaxwellBuchanan, Apr 09 2010 /the only thing coming out of it is the wire/
I like this raft used to power a light, also on the raft. Less wire. The raft would be anchored over at shallow spots dangerous to nightgoing boats, where it is also easier to anchor. This would be a great high school science project.-- bungston, Apr 09 2010 Bungston:
I've heard of solar powered bouy lights, but they tend to get cluttered up with nasty white seagull ****, and not to mention if you've ever used solar powered lawn lights you know that they don't work for very long. I think this would make an Awesome bouy light...would be a GREAT project and very doable because the circuit is so simple. One can use an ordinary rechargeable batteries for the capacitor I think.
A bouy light would be a great start, and then upscale and see how much power could be generated off the bouy perhaps power a transmitter too...I'm thinking you may want a small sail on top to make sure the bouy really rocks around a lot.-- ShawnBob, Apr 09 2010 Denholm:
The idea was for the tubes to lay horizontally across the waves and pivot along the center tube as the waves pass underneath, sloshing the magnets back and forth. Wanna build one in your garage?-- ShawnBob, Apr 09 2010 No sail, because think what will happen in a stiff wind: it will pull the tether tight, which will then be tight, limiting the rocking.
In fact this would be an issue regardless because of waves. I am not sure if buoys are tethered with simple ropes or with a rope in a pipe that tends to keep the buoy directly above the anchor.
You could start with a solar buoy light and replace the solar, because the rest of the piece will already be ocean durable.-- bungston, Apr 10 2010 Right: Nearly autonomous illuminated-navigational or weather-monitoring buoy for use in heavily-guano'ed areas. (Or for use in arctic, or antarctic winter). If that's the problem, then this is an elegant solution. [+]-- mouseposture, Apr 10 2010 mouseposture:
AND it would keep generateing at night too, unlike solar cells.
I'm liking this better and better.-- ShawnBob, Apr 10 2010 <link>-- jurist, Apr 10 2010 Jurist:
Wow! That pretty much proves the concept! I like it! They are moving a whole stack of magnets through a single coil. Unlike the raft notion however, there seems to be a moving seal and their magnet shaft moves vertically (not sure why). It seems like tilting motion rather than bobbing motion could be used to get rid of that dynamic seal even. Pretty much any wear items that make it more than an encapsulated plastic float are not ideal. Things need to be replaced etc. The optimal device would just sit there and make energy pretty with very very minimal maintenance.-- ShawnBob, Apr 10 2010 //vertically// actually I thought of the vertically too: sortof a spring arrangement, like a pringle's can; tilting seems better though... but your cores would have to hit the bottom before the raft hit the top of the wave and it tilted upright again.-- FlyingToaster, Apr 10 2010 I was thinking of a small float (innertube size) and a large magnet assembly. If the magnets were too great a % of the weight of the apparatus, they would keep that side down once tilted. The float needs to be large enough and magnet assembly (relatively) small enough that the magnets do not permanently weigh down one side.-- bungston, Apr 10 2010 Bungston:
You are so right! I'm thinking in |-|-|-|-|-| arrangement that the verticals (coils) in my little diagram would actually have to be two coils, each with a magnet, upper and lower so that the center of gravity never gets way out of whack like you just described.
As to springs, In fact, I saw an expensive version of the shake flashlight that had a second magnet in the back end such that when you shake it, it really springs the magnet back the other way.
Vertical or horizontal, springs (or extra magnets) in the end would be great to help reverse the movement of the magnets back the other way.-- ShawnBob, Apr 11 2010 Thinking more about this thing.
1: Probably a battery to charge would be good: no need for a light at night. I am sure the solar things do it this way.
2: Light should flash. Flashing light is less energetically expensive and more of an attention getter. Maybe solar buoys already do this.
3: I changed my mind about the battery. What an irritation, changing a battery. If the thing can rock on maybe dispense with battery.
4. The sail would be good for places like harbors where wave action is small. However getting a steady wind to rock something entails a sail which changes direction or shape as the raft is tipped, and then you have a nonenclosed moving part for the otters to chew on.-- bungston, Apr 12 2010 This idea is already baked, see wave energy link. The math and engineering behind wave energy devices is pretty baked, and already in use.-- metarinka, Apr 13 2010 Actually, the idea is not so much about wave energy itself as to the best way to do it...and how to do it without moving seals/turbines or wear items--that's not quite baked yet. A seagull crap-proof device...and nothing quite like this exists (yet). The closest thing is the link from University of Oregon, but in that one the magnet is tethered to the seafloor and the float moves, hence the moving seal (I think from the picture)...and actually this would use waveheight to move the magnet instead of rocking motion, which in very shallow water or surf even, tilting motion might be better.-- ShawnBob, Apr 13 2010 Sound like an ocean MHD power plant from my point of view.-- travbm, Oct 29 2015 random, halfbakery