Fresh water Hydrogen?

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  • #1
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Is Hydrogen a practical way to store energy and create fresh water?

Consider this scenario:

There is an island lacking a fresh water source. So you build some off-shore wind turbines. The electricity doesn't go far - just into the salt water at the turbine's base, where it uses Electrolysis to create hydrogen. The hydrogen then goes through a pipe to a high peak on the island. When power is needed, it is converted back to electricity, and water is created as well.

Would a tank of hydrogen hold enough to offset times when there is no wind? Would water created by hydrogen (fuel cells? Combustion?) be fit to drink? How much power is lost in turning electricity into hydrogen and back?
 

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  • #2
CWatters
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As I understand it the round trip efficiency of electricity -> hydrogen -> electricity is between 30% and 50%.

It takes about 50kWh to make 1Kg of hydrogen so of that you might get back 25kWh if you assume 50% efficiency. I think you also get 9kg of water. That means overall it would have cost you 25kWH to make 9kg of water which works out at 2.8kWH per Kg (or per L).

One reference I found says that desalination using the "SWRO process" (whatever that is) takes 6.8 – 8.2 kWh/kgal. Note that's per 1000 gallons!

So unfortunately I think your proposal has little merit. Would be much better to send the 50kWh of electricity ashore as electricity and use half to run a desalination plant.

Perhaps someone can check my numbers.
 
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  • #3
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Hmmm... It only "Costs" you 25 kWH if you had better things to do with the electricity at the time. If you are storing the hydrogen for later power generation, then the 30% - 50% might be better than chemical batteries or other methods of storage. Then the water would be a free bonus, although I see it isn't enough to support many people.
 
  • #4
Baluncore
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Once the turbine is installed you will find that the hydrolysis of sea water generates several gasses H2, O2 and Cl2.
You will need to dispose of the chlorine that will be mixed with the oxygen.
When you burn the hydrogen in air you will get water.
 
  • #5
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Chlorine? I wasn't expecting that.

So... There is a hotel on the island, and we put the chlorine in the swimming pools and pump the oxygen into the guest rooms? Everyone likes oxygen, right?
 
  • #6
SteamKing
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Chlorine? I wasn't expecting that.

So... There is a hotel on the island, and we put the chlorine in the swimming pools and pump the oxygen into the guest rooms? Everyone likes oxygen, right?
Well, if you're using seawater as the raw material for the desalination plant, what did you expect would happen when you ran a current thru the stuff?

Seawater contains traces (and some not so trace amounts) of just about every element there is on earth. The most common elements are found in this article:

https://en.wikipedia.org/wiki/Seawater

Not only will you accumulate chlorine and bromine, but you'll also soon have a stockpile of sodium metal and some sulfur to dispose of, not to mention Mg, K, and Ca.
 
  • #7
Baluncore
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So... There is a hotel on the island, and we put the chlorine in the swimming pools and pump the oxygen into the guest rooms? Everyone likes oxygen, right?
The oxygen and chlorine gas will appear at the same electrode. How do you intend to separate them ?
 
  • #8
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Hmmm...

Should I put all my dumb ideas here or start a new thread for each one? My next one is about electric cars.
 
  • #9
SteamKing
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Hmmm...

Should I put all my dumb ideas here or start a new thread for each one? My next one is about electric cars.
No, you should definitely start a new thread, since the subject has changed.
 
  • #10
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Well the wastage of nearly 50% is not so impressive . The electricity has to be send as electricity to the hotel or houses in the island. Then , the excess can be stored within batteries . Don't forget that the modern batteries last much longer specially considering how slowly they are being charged by wind turbines, solar panels etc. That electricity can be used for a desalination plant . The overall expense will be lower than your method .
 
  • #11
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The method people use in homes now is to store electricity generated by wind and solar using Li-Ion batteries. The efficiency there is pretty good. Modern Li-Ion batteries can charge and discharge with a loss under ten percent. Even lead-acid batteries can do quite a bit better than fifty percent efficiency. That's going to be hard to beat, but if you need hydrogen for purposes other than energy storage such as fuel for homes or vehicles electrolysis is a practical and easy way to produce it. Of course the more efficient way to go is to use electric cars and electric appliances. People have considered other unusual ideas on how to store energy, such as the potential energy of a mass in Earth gravity. That's actually an efficient method though it requires a lot of mass and the space for it to move.
 
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  • #12
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Can energy be extracted by burning the sodium and chloride back into salt? I take it that is where some of the energy from the windmill is lost.

I also recal someone saying that there was a ceiling to the price of lithium because it could be extracted from sea water. So it could be that my island's economy is based on exporting chemicals.
 
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  • #13
OmCheeto
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Hmmm...

Should I put all my dumb ideas here or start a new thread for each one? My next one is about electric cars.
I think this is a grand idea, and that you should finish this problem, before going on to the next.

Oh wait, that was in June! I'm guessing now that you.... Yup. Gas Trailer of EVs
That was also a grand idea, IMHO.

Anyways, getting back to this topic, I googled and found an interesting paper where they discussed your idea: Hydrogen Production Using Sea Water Electrolysis

Several problems pointed out earlier in this thread, seem to be solutions, pointed out in the paper, and by you.
You weren't one of the authors, were you?
 
  • #14
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You weren't one of the authors, were you?
I could claim to be. >:)
 
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