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Science

Underwater Power Generation? 62

Posted by Cliff from the natural-dynamos-under-the-sea dept.
An anonymous reader writes: "We keep seeing stories here about tidal power, and that's cool, but I don't see how it can be done without a column rising all the way to the surface. So here are the ideas I've got right now." Read on for some interesting thoughts on the subject...

"Keep in mind that the device will probably be housed in a length of 4-inch PVC or ABS pipe, and it needs about 0.5 ma at 1.5 volts:

  • Surge power. Put a couple of funnels back-to-back with a CPU cooling fan-sized turbine and generator in the middle, and run the output through a rectifier and capacitor. But how reliable will those moving parts be after years underwater?
  • Self-winding watch concept. Float the thing tethered to the bottom and install some sort of pendulum inside with a magnet on it, moving through a coil. The moving parts are protected, but will it be enough power?
  • Yank the chain. Again, tether it, but use the varying tension on the tether to drive a dynamo of some sort. Not sure how this would work.
  • Magnetohydrodynamic generator. Like the surge power thing, but using the flow of cunductive seawater through a magnetic field to generate a current. I have no idea how much power this would generate, if any, or how to deal with ion accumulation at the electrodes.
  • Nukes. Anyone got a spare radioisotope thermoelectric generator? Any idea how many smoke detectors I'd need to cannibalize to get enough Americium-241?
The generator need not fit inside the 4-inch cache tube, but it shouldn't be huge, either. It needs to be practical to build, and not terribly expensive. Above all it's got to be reliable and enduring. Any ideas?"
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Underwater Power Generation? More

Underwater Power Generation?

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  • I'd love to help you... (Score:3, Funny)

    by Anonymous Coward on Tuesday April 02, 2002 @10:49PM (#3274649)
    But first you need to tell us who you are and why you want and underwater lair.
    • Gah, you've discovered my evil secret! I suppose I may as well give you all the details. I am Man-Ray, scourge of the oceans and destroyer of land-dwellers. Soon, my perpetually blinking submarine LED devices will be placed in all of the world's oceans, a constant reminder of my aquatic domination to those who might venture into my domain! Muahahahahahaha!

      And stay off the lawn, damnit!

  • Dangerous (Score:2, Funny)

    by 0xB ( 568582 )

    You do realise that by extracting energy from the sea you will be affecting the currents and temperature gradients, and this will have a knock on effect on the weather?

    You may think 0.5mA is not much, but just wait until Canada turns into a barren desert and then you'll be sorry.

  • Bubbles? (Score:2, Funny)

    by n2linux ( 261477 )
    How about harnessing the power of underwater fart bubble? ;-)
    • How about harnessing the power of underwater fart bubble? ;-)

      Yeah, split the "fart atoms" for a remarkable source of power. Especially after burrito night! ;p
    • Man, White Castle's business would BOOM!
    • What type of terrible thing would you have had to do to end up getting a $h1tty job like that?
      Or would that be a job for the illegal imigrants?
      And would it pay minimum wage or would it be hazzard pay ?
  • Wasnt that yesterday?

  • Great Writeup! (Score:1, Offtopic)

    by jordanb ( 322398 )
    Wonderful to finally see Slashdot authors manage to put up a story with no spelling or grammar errors on the front page!
  • this comment is just as insightful and funny as the empty blurb on the main page. so in *theory* this should boost my karma. why are my theories always wrong?

  • Piezo electric rods... (Score:4, Insightful)

    by Perdo ( 151843 ) on Tuesday April 02, 2002 @11:30PM (#3274849) Homepage Journal
    piezo electric rods placed along the coast to capture the energy of wave motion and tidal effects. Unstable airfoils could be placed on top to "play" the rod even during relativly calm periods. In vast mumbers, They would provide two benifits: Act as bariers to coastline erosion because they would absorb the energy of coastal wave action and The generation of electricity of course.
    • The problem with this is cost vs scale. Additionally, you aren't even putting a significant dent in erosion with a plan like this. You're just transplanting it. If it's not falling into the ocean, you're digging it out of a BIG DAMN HOLE somewhere else to protect that there coast line.

      Skip the science. Focus on phonics.
    • Golly, I bet they could be used to power a spell-checker, and perhaps a grammar-checker can be added once they've been perfected!

  • Channels (Score:4, Insightful)

    by Deanasc ( 201050 ) on Wednesday April 03, 2002 @12:27AM (#3275045) Homepage Journal
    The currents through some channels are well known and steady. Put underwater "windmills" in the channel and sit back and collect the "juice". This is similar to sailboats that tow small electric generators or put magnets on the propeller shaft to trickle charge the batteries.

  • 6 watt hours per year. (Score:4, Insightful)

    by hamjudo ( 64140 ) on Wednesday April 03, 2002 @01:03AM (#3275170) Homepage Journal
    I must have missed something, check my numbers.
    .0005 amps * 1.5 volts * 24 hours/day * 365 days/year is 6.13 watt hours per year.

    If your circuit could tolerate voltage droop, a single D-cell would run it for a few years. But voltage droop is probably annoying, so put in a few D-cells and a voltage regulator.

    Alkaline batteries aren't rated to last more than 8 years or so, so use lithium batteries if you need something good for decades.

    We need to know how many years this should work to give you more precise advise.

    I can think of lots of ways to produce 0.75 milliwatts, just none of them will be more reliable than a lithium battery.

    • Re:6 watt hours per year. (Score:5, Informative)

      by Rorschach1 ( 174480 ) on Wednesday April 03, 2002 @01:51PM (#3277960) Homepage
      If the /. 'editors' hadn't mangled my submission, you'd have seen that I already considered that. Here's the full thing:

      Ok, so I've gotten into this geocaching [geocaching.com] thing lately, and while working on a cache to be hidden in about 60 feet of water off the coast, it occured to me that a blinking LED might make it easier for divers to spot. No problem, whip up a blinker circuit with an LM3909 [national.com] and a super-bright green LED [lumex.com] and we're set. But what about power? Sure, four D-cells [duracell.com] would let it run for close to a decade, but where's the fun in that? The undersea environment is quite dynamic, and there's got to be some power down there that can be harnessed. What I need are some ideas on how to do that.

      We keep seeing stories here about tidal power [slashdot.org], and that's cool, but I don't see how it can be done without a column rising all the way to the surface. So here are the ideas I've got right now. Keep in mind that the device will probably be housed in a length of 4-inch PVC or ABS pipe, and it needs about 0.5 ma at 1.5 volts:

      • Surge power. Put a couple of funnels back-to-back with a CPU cooling fan-sized turbine and generator in the middle, and run the output through a rectifier and capacitor. But how reliable will those moving parts be after years underwater?
      • Self-winding watch [timezone.com] concept. Float the thing tethered to the bottom and install some sort of pendulum inside with a magnet on it, moving through a coil. The moving parts are protected, but will it be enough power?
      • Yank the chain. Again, tether it, but use the varying tension on the tether to drive a dynamo of some sort.
      • Nukes. Anyone got a spare radioisotope thermoelectric generator? [nasa.gov] Any idea how many smoke detectors I'd need to cannibalize to get enough Americium-241 [uic.com.au]?
      • Magnetohydrodynamic [ntlworld.com] generator. Like the surge power thing, but using the flow of cunductive seawater through a magnetic field to generate a current. I have no idea how much power this would generate, if any, or how to deal with ion accumulation at the electrodes.

      The generator need not fit inside the 4-inch cache tube, but it shouldn't be huge, either. It needs to be practical to build, and not terribly expensive. Above all it's got to be reliable and enduring. Any ideas?

      • That makes more sense.

        So the requirements are something that lights up, is nifty, not too expensive, non-hazardous, and works most of the time.

        So something that went dark during periods of unusual calm would be ok.

        I doubt anything will outperform a lithium cell in any respect except for being more nifty.

        Most of the devices I can think of, will stop working if they get coated with living stuff. How long does stuff stay clean 60 feet down?

      • I've seen what storms on the gulf coast of Florida can do to underwater rock structures, so I have to wonder how you are going to keep your geocache from getting dislodged during rough seas?



        -Chris

  • You are giving us very little information. But here's what I'll do for you: I'll answer your problem and make it quick, easy, and (most important) CHEAP.

    Use a D cell. Yep, your common flashlight battery will supply you with 3.8 years of power at your requirements, and best of all no moving parts!!! If your device lasts half that long underwater then I'll officially be surprised. Need longer time? Use two cells! More power? Go lithium!

    Of course, there could be legitimate reasons to not use the cheap, widely available chemical power you can buy at your grocery store (maybe your gov't grant requires you to buy $400 hammers as well or something), but if you posted info relevant to the question, and why painfully obvious solutions have been thrown out then we could get somewhere.

    If these are home built one-off projects, I'd definitely ditch the generator concept. It's far too problematic, and will not last anywhere as long as a lantern battery, and probably not as long as the D cell quoted above. If these are research devices, I'd ditch it unless it was actually the whole point of the research (which I suspect). If this is part of your report/dissertation/homework/etc then do your own work. If this is a commercial product, tell us your market, price range, longevity, and what it's actually powering.

    -Adam
    • Augh. Wait, wait. You want to put alkaline batteries underwater? There's two other problems that you need to consider then:

      • Corrosion. The impression I get (correct or not) is that the device is supposed to have a long lifetime, be small and relatively inexpensive, and perhaps numerious. In those circumstances, the chances of salt water leaking into the battery enclosure sound pretty good. Once that happens, end of life follows rapidly.
      • Leakage. End of life occurs because the acids from the battery leak out into the surrounding seawater. I hate to sound like a treehugging owllover, but contaiminating other organisms habitats with extremely toxic chemicals they've got nearly no protection against just strikes me as uncool. Depending on placement and ubiquity of the planned device, you could be talking about serious ecological damange. And probably hefty fines, to boot.
      • Hey,

        There's two other problems that you need to consider then:

        Buy yourself a small tupperware container. Put your electronics in. Drill a hole for any cables to come out of, and seal it up with silicone sealent, from any good hardware store. Put silicone sealent around the top of the tupperware box, and place it on.

        Allow the sealent so set and voilia, one long-life sealed container.

        Michael
      • If he cannot build a watertight battery compartment, what chance in heck does he have of building a generator?

        It is true that a battery subject to adverse conditions will leak, but that goes again toward engineering a good battery compartment, and buying good batteries that are suited to low drain applications.

        I still say that it'd be far better than any generator scheme he could come up with. There are reasons he might not want to use batteries, but the ones you mention are cop-outs to cover incapable engineers.

        -Adam
        • If he cannot build a watertight battery compartment, what chance in heck does he have of building a generator?

          Watertight I've no doubt of. Survive ocean submersion for the decade or more he seems to want it for is more difficult. Maybe cast the whole thing in silicone and without air pockets. Frankly, he'll be putting it in an environment that most plastics and metals fair poorly in, and probably changing it's ambient pressure constantly.

          Further, comparing the difficulty of a battery compartment to the difficulty of a generator is disingenuous, I think. What I'm cautioning against is not the difficulty (which I think is about the same, and made quite arduous by the proposed lifetime and environment); I'm concerned about the consequences of an engineering failure.

          If almost any of the generation ideas he proposes goes south, worst case is that the device stops working. If a battery compartment leaks, the battery leaks alkalines or lithium compounds into the surrounding seawater.

          That's my two cents.

          • Lithium in particular doesn't play well with water. To tell the truth, right now it looks like I'll probably just be using 3 or 4 alkalike D-cells (Duracell says they should be ok for years, especially at 50 degrees F) and sealing it all up with epoxy. The only opening in the pipe will be for the LED, which will be epoxied in place. Hopefully the lens can take immersion in salt water.

            I thought about pressurizing the pipe to help counteract the outside pressure, but I just recently had a bad experience with pressurized ABS (spudgun experiment) and I'm wary of trying it again. The window replacement alone cost me $25 last time...

            Yeah, batteries are the easiest way to go, but I just like the idea of trying to make an ultra low-power circuit run indefinitely (until component failure) unattented, without access to solar power.
    • See my reply to the message above. Moderators on crack? It's the editors we've got to worry about. =]

  • Differentials (Score:4, Informative)

    by Nyarly ( 104096 ) <nyarlyNO@SPAMredfivellc.com> on Wednesday April 03, 2002 @02:39AM (#3275467) Homepage Journal
    I wonder if the device couldn't be placed with an end on either end of a thermocline.

    The idea would be to use the temperature differential (which can be significant - 10 degrees Faranheit isn't unusual) to generate current. A decent thermocouple would be able to do this without too much difficulty.

    The difficulty, of course, is getting the thermocouple on either side of the thermocline. If the device can be of sufficient length (describing it as housed in a pipe suggests as much) this shouldn't be an issue. However, remaining on the thermocline could be difficult. Perhaps some sort of diaphram that would maintain position at the boundary? Tricky.

    • That's fairly similiar to open/closed OTEC concepts. The problem with this scenario is that you're limited to a (relatively) narrow set of latitudes where you can expect to get both sufficient temperature differential for your thermocline, and enough energy to make it worthwhile.
      • For your power requirements, skip the generator entirely. Slap on a decent battery and a couple of solar cells to keep em juiced.

        Unless you're doing all this underwater, which wouldn't make sense given the examples you put forth.

        • Re:Differentials (Score:4, Interesting)

          by Rorschach1 ( 174480 ) on Wednesday April 03, 2002 @02:22PM (#3278195) Homepage
          Yeah, it's all underwater. See post about editors on crack.

          There can still be a considerable amount of surge at depth. I remember finding one roughly 1-meter hole in a rock wall near Anacapa that funneled the surge through it with enough force to knock me around and almost tear the regulator from my mouth, and then suck me through and spit me out the other side. It'd be able to generate tons of power, but it'd be way to heavily travelled a spot for my purposes. (See post about underwater lair. =])
  • A few weeks back there was a story about Wave Motion power plants [slashdot.org]. There were links there to other experiments with power generation from wave/tidal foreces.

  • make a fan (Score:3, Interesting)

    by marcus ( 1916 ) on Wednesday April 03, 2002 @03:16PM (#3278579) Journal
    Requires:

    1 large weight for the base
    piezeoelectric device
    1 foot by 1 foot flapper of suitable material
    LED
    some silicone goop
    case of some sort

    Build the flapper with one corner attached to a short arm and the arm to the piezo device. Wire PD to the LED. Fit circuitry, everything except flapper and half of the arm into the case. Anchor non-flapper-arm side of PD to case. Fill with goop. Take a dive and anchor the device on the bottom with the flapper aligned to wave surge and you're done.

    LED will pulse when wave surge pushes flapper. 2 LEDs will allow for pulses both in and out.

  • I agree with those that say use batteries... (Score:3, Insightful)

    by cr0sh ( 43134 ) on Wednesday April 03, 2002 @06:08PM (#3279983) Homepage
    Coupled with resin or silicone potting (as others have suggested), it seems the best, most reliable, and cheapest way to go.

    But, there is another option, though it probably won't last as long - think seawater and different types of metal...

    That's right - akin to a "spud/lemon - battery" - if such a thing could power a small watch, then it could be scaled up a bit to power an LED...
    • The spud/lemon battery is a fairly simple device, but the electrodes will suffer from corrosion quite easily. The metal oxides, the algae and other living creatures on the electode surface will decrease the current quite significantly.
  • I have absolutely no idea how much power these watches can generate (probably not anywhere near enough, but it would be a fun experiment :-).
    Get yourself a seiko [seikousa.com] kinetic watch, which generates power by movement, and stores it in a very efficiënt capacitor. Throw out the clock, and use the mechanism (or a couple of mechanisms, either parallel, in series or a combination of boh depending on the power requirements) to power your blinkenlight.

    Seal aforesaid device in a package with enough air so that it floats. Attach a large weight with a thether to it, dump it in the surf and hope that it works :-)

  • Longevity problem (Score:1, Interesting)

    by Anonymous Coward
    If you're thinking long life (greater than 10 years), wouldn't various forms of life become problematic? (i.e. coral, seaweed, algae, sponge, etc.) Even if your moving parts aren't all gunked-up, who's going to see an LED covered in coral? Are there any low-power GPS type devices? Since you're assuming someone will be close enough to see an LED, wouldn't a hand-held unit communicating with a BlueTooth-type device be adequate? Using a capacitor-charging system, you could give pulses as infrequent as every minute or so, if needed.

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