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Old 04-04-2010, 12:31   #1
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Hydrogen Tanks

If you are like me, there is a fair bit of time in sunny weather when the batteries are full, and the solar panels are shut off by the regulator.

I was thinking I could generate hydrogen with the excess power and keep it in a pressurized tank. The idea is to put 5 or 6 electrolysis cells in series with stainless steel plates, and use either sodium hydroxide, or sulfuric acid in fresh water (to make it conductive)

The electrolysis will automatically pressurize the gas, so a pump wouldn't be needed. Then the possible uses for hydrogen (and oxygen) generated include:

1. Torch, welding, cutting metal
2. Cooking stove fuel
3. Fuel cell (I found a fuel cell which can put out 1kw for $4000)
4. Engine.. in theory it should be possible to convert a 4 stroke gas engine to run on hydrogen.


I am sure there are other uses (feel free to discuss) but I am mostly interested in the first two.

Does anyone have experience with this, or ideas for such an aparatus? It would probably be best to store hydrogen and oxygen separately so a normaly welding torch can be used, and use less oxygen 4:1 mixture instead of 2:1 (so the metal being welded doesnt oxidize) but I would be happy to start out with something that stores HHO too.
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Old 04-04-2010, 12:44   #2
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I agree that it's vexing when the batteries fill up and you've got no where else to store energy. This happened to me yesterday: by 1300h both the wind generator and solar panels had gone into hibernation mode. We were on the beach at that point, keeping an eye on the boat while it lied at anchor, and therefore couldn't do our normal trick of converting excess energy into hot water via the inverter.

But a $4k fuel cell just to store excess energy? Yikes. That sounds like the type of plan congress would come up with.

What I'd love to see would be a system where the charge controller, rather than shutting down the panels, would throw excess energy into a 12v heater in the hot water system. How cool would that be?
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Old 04-04-2010, 15:11   #3
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Wow!! Sounds like a good way to blow up yourself and your boat. I am a retired chemical engineer. Here are a couple of obvious problems with your scheme. There are dozens of others.

The hydrogen generated by an electrolytic cell is at quite a low pressure. It will take two independent compressors to compress the gas to storage pressures (1000s of lbs for O2, ? for hydrogen). Your welding torch probably needs at least a hundred pounds of pressure supply to work at all.

Fuel cells don't need much pressure at all, but storing H2 and O2 at low pressure will take huge volumes of tankage.

Need I say more?

David
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Old 04-04-2010, 15:22   #4
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More batteries anyone?
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Old 05-04-2010, 02:26   #5
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Quote:
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But a $4k fuel cell just to store excess energy? Yikes. That sounds like the type of plan congress would come up with.
Yeah, too high a price for me, but it might be possible to build a low-efficiency fuel cell, or just not get one until they are cheaper.

Quote:
What I'd love to see would be a system where the charge controller, rather than shutting down the panels, would throw excess energy into a 12v heater in the hot water system. How cool would that be?
That should not be very hard to do. A potentiometer, 2 resistors, and opamp and a relay or mosfet could do this. I think I will set something like this up soon.. The part I dont like is the fact that the batteries need to be fully charged to maintain them (not lose capacity over time) but the charge voltage changes with temperature. To do this I would need to reprogram the microprocessor in my charge controller, or make a circuit with a microprocessor and temperature sensor in it.. this shouldnt be too difficult, just kind of boring work.


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Wow!! Sounds like a good way to blow up yourself and your boat. I am a retired chemical engineer. Here are a couple of obvious problems with your scheme. There are dozens of others.

The hydrogen generated by an electrolytic cell is at quite a low pressure. It will take two independent compressors to compress the gas to storage pressures (1000s of lbs for O2, ? for hydrogen). Your welding torch probably needs at least a hundred pounds of pressure supply to work at all.
No it only needs 5psi. The torch has regulators to drop high pressure down 5psi. Same regulator could probably be used for a fuel cell.

As for compressors, I don't think any are needed. The reason is electrolysis itself creates the pressure. As for how high a pressure you could achieve, I am not entirely sure.

Maybe instead I should try to build a vanadium flow battery?
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Old 05-04-2010, 04:44   #6
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Perhaps 5psi will work for a torch but to store any significant quantity of hydrogen at only 5 psi would require a tank as large as your boat.
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Old 05-04-2010, 05:39   #7
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Sounds great, if a little dangerous.

The electrolyte may need variation - a much more efficient medium than brine is available in profusion on any boat Producing hydrogen from urine

Recycle, recycle.

Bill
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Old 05-04-2010, 07:32   #8
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Quote:
Originally Posted by Bash
What I'd love to see would be a system where the charge controller, rather than shutting down the panels, would throw excess energy into a 12v heater in the hot water system. How cool would that be?
I think this is what you're looking for... watercoil
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Old 05-04-2010, 07:33   #9
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Space, weight and money are the three problems that I see. This would also make your life I think unnecessarily complicated. Additionally, the more complex a system, the more likely it is to break unless it is engineered really well and time tested. Your system would be a prototype.
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Old 05-04-2010, 07:54   #10
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I think this is what you're looking for... watercoil
don't forget the dump load controller....
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Old 05-04-2010, 08:20   #11
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I'd love to see this happen

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Originally Posted by geckosenator View Post
That should not be very hard to do. A potentiometer, 2 resistors, and opamp and a relay or mosfet could do this. I think I will set something like this up soon.. The part I dont like is the fact that the batteries need to be fully charged to maintain them (not lose capacity over time) but the charge voltage changes with temperature. To do this I would need to reprogram the microprocessor in my charge controller, or make a circuit with a microprocessor and temperature sensor in it.. this shouldnt be too difficult, just kind of boring work.
would a dump load controller, such as denverdOn suggested, work better?
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Old 10-11-2010, 14:46   #12
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Independence yacht

Visit Independence greenyacht web pages. It is a solar/hydrogen fuel cell boat with 1.200 mile range. It does not use fossil fuels, only sun and water.
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Old 10-11-2010, 15:41   #13
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Electrolysis of seawater is not very efficient. Around 30% at best. A better storage mechanism would be compressed air. Running a 12volt compressor into a tank that ran an air engine. There is a car that runs entirely on compressed air. As the technology becomes more mature an air powered engine could provide auxiliary propulsion or run a generator.
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Old 10-11-2010, 15:50   #14
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Re. excess solar power: Dumping it as heat (eg. into the water heater) is a logical way to use it, if you're going to use it. Or you could enlarge the house battery bank. Or indulge in a little luxury- fire up the air conditioner, for example. (edit- Bill's suggestion of compressed air is also a good one; tools that run on compressed air are cheap, plentiful and reliable)

As for hydrogen: This could be a long, complex story. The short version is that, at present, we simply don't have the technology to use hydrogen as an economically viable energy storage medium. The car industry is working furiously on this problem, but a solution is a long way off. For the moment, it has to be stored compressed (often upwards of 10,000 psi, at which point exotic composite tanks must be used as it'll leak right through steel) or as a cryogenic liquid (which takes an enormous amount of energy and complex storage tanks); hydrogen storage in metal hydrides, etc. can, for now, be done only in the lab. Also worth noting: Hydrogen can only be electrolyzed from fresh water, not from salt water- and we all know how watermakers love to suck power.

Re. Independence yacht - It's a nice concept. From what I've been able to find on it in the last few months, though, there are two problems holding it back:
(1) the published speed and range estimates don't match with known limits of the technologies employed (6.6 kW of solar array produces at best about 60 kWh/day, usually less- a day of sitting in bright sun will only spin the twin 75 kW motors for about 15 minutes at full power with very optimistic estimates of the various losses involved- not counting house loads), and
(2) so far, there's no evidence that it is being built. As presently specified, it would be capable of running around the harbour on the weekend, and not much more.
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