# idea to generate electricity from wave energy

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Hi,

I came up with an idea to generate electricity from ocean waves, and was wondering how it compares to other methods. Basically there is a heavy floating vessel riding the wave, and a steel rod attached to it going down to the seafloor. At the seafloor there is a vertical hydraulic cylinder with a length equal to the ocean wave amplitude. The steel rod is connected to the piston of the hydraulic cylinder, and the up and down action of the waves run a rotary hydraulic motor using the up down action of the piston. This hydraulic motor shaft is attached to an electrical generator. There are a couple more details too like a rod guide above the cylinder to keep the piston aligned, and a concrete base around the cylinder to make the devices deployable by ship.

Also since this is an electronics newsgroup, here's an electrical analogy: the waves are the voltage signal and the seafloor is the circuit ground, and the load is the hydraulic fluid movement :) Higher voltages (wave amplitude) equals more power!

cheers, Jamie

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I've already told the UK gov how to do nuclear fusion the easy and safe way so they aren't really bothered about that sort of stuff.

You can't have none because they haven't worked out how to say 'Yaa Boo sucks' to each other or the rest.

Apparently that sort of stuff is really complicated.

DNA

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Why not leave the ship mobile and just sink a flat platform under the vessel in the horizontal plane, it will resist the verticla movement of the vessel. Connect that to the piston you setup on the vessel with your generator.

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John

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Theres a lot of forces at sea, ive seen pictures of some very bent protoype wave powered generators, also errosion etc ..

I was wondering if the pressure at the sea bed changes much as a wave passes over, if this could be used it would mean just a flat object on the sea bed, wich would be least intrusive and probably least exposed to damage.

Colin =^.^=

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If you do a little math, the numbers don't come out too good. Assume you can build it for \$10 per ton of displacement, and the water moves up an average of a meter every 5 seconds. From that calculate the horsepower per ton (550 ft-lbs/sec is one HP). Doesnt even pay the cost of borrowing the \$\$\$\$ to build it.

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Not much, about 0.445psi per foot of wave height.```
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passes

hmm doesnt sound a lot, although I gues for 40ft waves it might be though, I would think it also depends on the depth/wavelength ratio too, I wonder if that would source a useable amount of power.

ie. to pay back the energy used to create the device in a reasonable time

My idea was to have a simple enough device to make it very cheap, wich is like a flat square accordion type box wich is just installed on the sea floor, the ar/liquid inside it is connected to two pipes via one way valves (in oposite directions), maybe need a piston inside, it would rely on at least two such units spaced far enough apart so that they have different pressure on them, the two pipes go to a turbine or whatever.

Obviously the moving accordion squeezy type bits need some carefull thought. and the pipes would have to be well secure too. not to mention the delivery of the energy to the shore.

The main advantage would be that it is able to cover as large as area as available as it is virtualy totaly unobtrusive. If it was constructed right it would allow any silt/etc to just rest on top and go up and down with the units.

It might be possible to fabricate a realy huge mat of these things and then just let it drop to the sea floor, if the total mass is enough it might just stay put with virtualy no further instalation, although it would be cheaper if they were able to be made out of plastic.

Multiple redundancy would ensure a significant number of failed units would not stop the whole thing from working.

However im not convinved that you get enough alternating pressure differential between units on the sea floor at a reasonable depth. if there was that pressure differential then you would presumably get a current on the sea floor too, maybe this is so ?

Im not realy into the mechanics of these sorts of waves but the idea of finding a truly ideal alternative energy source is too good to miss.

Colin =^.^=

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You expect to find two places in the ocean that are at different pressures, and deliver these pressures to an accordion box? Try an experiment in your bathtub with some plastic tubing. I think you'll have a really hard time finding *any* pressure difference gets delivered to the box. Hint: If there was a pressure difference, why wouldnt the higher pressure zone push against the lower pressure one until the pressures average out?

Also pressure is not energy. Pressure has to work over a distance to supply work. For instance, the pressure at the center of the Earth is many trillions of pounds per square inch, but there's no energy being expended and no work done.

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Why not just a paddlewheel? You could put a weight below it to stablize it and attach it to the sea floor with a chain and let the water current turn the wheel to generate power. Would be cheap but I don't know how effective and I suppose it would be easy to get jammed. Not sure how much power it would generate though. (if it was a lot then many ships could attach a similar rig to the hull and use it to regain back some of the power)

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This was how Count Belisarius maintained Rome's bread supplies in 537AD, when the besieging Goths destroyed the aqueducts that fed the watermills. He had the mills rebuilt on boats anchored in the Tiber. The boats were arranged in pairs with the wheel between them.

Paul Burke

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What current? Unless you're in a tidal basin with the tide going in and out, the ocean mostly just sits there for all practical purposes (ignoring deep sea circulation currents driven by temperature differences and so forth). The water comprising waves goes up and down, with little back and forth motion.

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Waves do not have significant energy in the horizontal direction. It's mostly up and down. But you know this if your tennis ball has ever gone over the fence into a lake. It doesnt come back to shore-- it tends to stay in one place.

The way a surfboard extracts energy is that it's on a slope, and the slop is moving "forward".

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Well no im not sure if there is a pressure differential deep down or not, but if a 100ft tsumani washes over you while you are sitting on the beach, all of a sudden you will find the pressure has definatly changed !

The height of the water above one spot varies with the wave, wich at some point must cuases a change in pressure but below a certain depth this probably disapears, as you say if there is a pressure difference this will cuase a water flow wich would cancel it out, however it is a wave and so it is rather dynamic, the momentum of the water will mean the difference exists for a while before the water can start to move, by wich time the pressure may have changed back.

However The flow of water in the pipes is in one direction, so momentum doesnt impede the flow.

The work comes from the difference in pressure and the movement of the accordians cuased by the change in pressure, the constant pressure is of no consequence to this. The accordians move up and down with a relative 'difference' in pressure on them, this is the distance*force (force=pressure*area) that is energy.

I did think of the tubes in the bathtub but a comprehensive mathmatical model would probably show a more realistic idea of whats going on. Its all a question of what depth the presure disapears, but I think it is probably rather complicated.

Colin =^.^=

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And sooner or later, a storm will blow structures like this away. After all, one does put them where the waves get big.

John

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That was all parody, right?

John

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Hey, congrats - you have discovered zero point energy. :)

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There was something to this scheme in an old mechanics illustrated magazine sometime back. But they envisioned large turbines anchored to the sea floor in a fashion similar to the wind mill generators, that take advantage of sea currents.

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Thats not true. There are many real examples of this not being true. The gulf stream is a prime counter example.