long term heat storage

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long term heat storage

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Slim

Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)

Posted: Thu Jan 12, 17 12:49 pm Post subject: long term heat storage

https://newatlas.com/renewable-energy-heat-storage-empa/47334/

Interesting idea. I would have thought that NaOH would be an undesirable choice in terms of system longevity. (Won't it eat away at pipes, etc...?)

Quick google, and apparently NaOH is okay in appropriate stainless steel plumbing, if below 80 C https://www.bssa.org.uk/topics.php?article=34

Anyhow, clearly just the begining stages of this idea, but still an interesting one. I'm curious how the heat transfer and storage efficiencies work out. (Is it really that much better to use the lye to heat the ground in the summer and pump it back out in the winter than it is to use more conventional geothermal heat pump technology?)

Mistress Rose

Joined: 21 Jul 2011
Posts: 15996

Posted: Fri Jan 13, 17 8:04 am Post subject:
I'm not sure about this. I am very much aware that 'solid' sodium hydroxide will generate large amounts of heat in contact with water, but I am not sure that this occurs as dilute as 50%.

Slim

Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)

Posted: Fri Jan 13, 17 12:26 pm Post subject:

Mistress Rose wrote:

I'm not sure about this. I am very much aware that 'solid' sodium hydroxide will generate large amounts of heat in contact with water, but I am not sure that this occurs as dilute as 50%.

Yes, the article is sufficiently vague to not really know what it is they're doing. Are they hydrating and dehydrating NaOH? Or are they using geo-heat pump to store heat in earthen thermal mass.

I think to your point, the exact question is whether there is still an exothermic reaction when you keep adding water. A quick google says that 50% is the saturation point for a NaOH solution, so I don't know how they would be further hydrating lye and getting heat out.

Maybe the article is incorrect, and they meant that the solution would be at 50% NaOH after they got as much heat out as they could, and that is the point where heat would be applied to dehydrate the solution and "store" heat for later.

As I type, I realize that would put the solution above 50% and NaOH would begin precipitating out, so how would their solution flow.......

In short, I'm curious to know more about their supposed setup, and I hope the article isn't just bogus.....

EDIT: As always, best to go to the source: https://www.empa.ch/web/s604/naoh-heat-storage

Mistress Rose

Joined: 21 Jul 2011
Posts: 15996

Posted: Sat Jan 14, 17 8:52 am Post subject:
I think the original article said that the heat was stored in 50% solution and diluted to 30%, but not sure that sodium hydroxide gives out heat at those concentrations.

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