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Small scale tidal power

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Although harnessing the tides for electrical (or mechanical) energy is not new, it's not widely implemented, because, basically, you need to dam a bay. The Bay of Fundy, which expereriences the world's largest tides, is one location that produces tidal electricity. My idea is for a much smaller scale design that might be able to power your house, or perhaps pump sea water into a de-salination tank, or some such thing. Basically, the device would be anchored to the bottom of the ocean by a post (with gear notches along one side), just a bit further than the low tide mark. A floating section, provided by a large boyant device would then float on the surface of the water. The relative motion between the boyant section and the post would produce energy, via a gear system that engages the teeth on the post. Obviously the relative motion is quite small... a tide may only rise a few feet. The brawn comes from how you implement the gears, and how much force the floating section can produce. Unforuantely, I have not figured out how you'd generte any power from an outgoing tide via this method. You'd want the floating section to be fairly light, and having it ride the ocean back to low tide wouldn't produce enough force (only the force of gravity) to generate power.
 — mtoonsdale, May 17 2004

Gravity Ram http://www.pathcurv...yRam/principles.htm
Similar but bigger [ben_krak, Oct 04 2004]

Forbes article on Tidal Electric http://www.forbes.c.../2003/0721/042.html
[spacemoggy, Oct 04 2004]

Tidal Electric http://www.tidalelectric.com/
Homepage of the company building the tidal lagoon [spacemoggy, Oct 04 2004]

I've done some more figuring on this... maybe it's not all that great an idea afterall. Work = Force x Distance. So, assume 100,000Kg of boyant force (large, I know, and I also know a Kg is a unit of mass, not force, but you know what I mean), which equals 980,000N of force. Assume the tide is 3 meters from high to low. 980,000 x 3 = 2.94 Megajoules of work. Power = Work / Time, so 2,940,000 Joules /43,200 seconds (12 hour tide) = 68.06 Joules per seconds of power, or in more appropriate terms, 68.06 watts of power. Not even enough to run a couple 40 watt light bulbs. I still like the idea, even if the math proves its impracticallity.
 — mtoonsdale, May 17 2004

for a small device I think you are better off capturing the current with a turbine or even capturing the wave action.
 — macrumpton, May 17 2004

//you need to dam a bay.// Thats the old way. At Swansea, in Wales, they're building the world's first tidal lagoon. This has myriad advantages over damning a bay. It prevents silting, the tide can be used on the way in and the way out, and it can be built in lots of places. For a look at the future of electricity generation, see links.
 — spacemoggy, May 18 2004

[mtoonsdale], perhaps it is easier to think of the energy available as the work done to lift a volume of water from low tide to high tide...:)
If you reduce your scale further, then every time a wave passes it is like a fast moving mini tide. There are plenty of wave generation devices in use already.
 — Ling, May 18 2004

 The Rance barrage is built across a river. It is tidal, but there are several drawbacks to it: 1) electricity can only be generated on the way in, as if you disrupt the outward stream the area behind the barrage will silt up. 2) the barrage prevents fish swimming upstream to breed, and generally disrupts the ecology. 3) suitable sites for barrages are limited.

There was a plan to build a large tidal barrage across the Severn Estuary in South-Western England, but it was scuppered by protests from local environmentalists and surfers. The surfers were furious that it would stop the Severn Bore, which can be surfed for miles upstream.
 — spacemoggy, May 18 2004

Although daming a bay may be the old way [spacemoggy] implies that the tide can't be used going out AND coming in with this method. But it can be, and is. Also, 'damning' a bay is different than 'daming' one.
 — mtoonsdale, May 19 2004

And damming is different from damning....
 — Ling, May 19 2004

Well, I was specifically referring to estuarine bays, which the Rance Barrage is. I suppose there's no reason why a bay that doesn't enclose a large river shouldn't generate power on the way out and the way in. But most tidal barrages seem to be built across estuaries, and you then get the silt problem if you generate power on the way out.
 — spacemoggy, May 20 2004

Drat. I was hoping for something for my bathtub.
 — DrCurry, May 20 2004

guys, speaking as a completely shag-wit here, would an underwater wind farm [sic] not be a more pratical and efficient way to harness tidal power. Would leave surface passage open to shipping and be directionable (?) to harness both in and out tides? I'm thinking lots of small to medium size turbines not the ginormous (its a word!) ones.
 — etherman, May 20 2004

 //it's a word!// So you say. But you try that in some of the rougher scrabble-bars around here, and see where it gets you.

Luke: I'll be careful... Ugly alien: You'll be DEAD!
 — spacemoggy, May 20 2004

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