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Underwater Power Generation?
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?
But first you need to tell us who you are and why you want and underwater lair.
just wait until Canada turns into a barren desert and then you'll be sorry.
You sure about that, eh?
Hey Taco! Looks like you're using the "infinite monkeys and typewriters" scheme to generate Ask Slashdots again...
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.
If voting were effective, it would be illegal by now.
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.
I've hit Karma 50 and gotten a Score:5, Troll... I win!
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.
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.
IP is just rude.
Is there any torture so subl
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.
IP is just rude.
Is there any torture so subl
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.
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.
Good judgement comes from experience, and experience comes from bad judgement.
- W. Wriston, former Citibank CEO
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...
Reason is the Path to God - Anon