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Author Topic: Why Channel Energy Into Molten Salt ?  (Read 10202 times)

Offline jgchemie

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Why Channel Energy Into Molten Salt ?
« Reply #25 on: 10/10/2011 22:48:21 »
The big problem with electricity generation from solar is, of course, that the sun only shines during the day ::)  To get a good price from the electricity grid the generating station should be able to track demand as best as possible - So, for solar, this means storing a large amount of it's available energy after the sun has set.


So the engineers are looking for the best material that can:
- absorb a lot of heat in the range that the solar station can use (at temps suited to raising superheated steam).
- can take-on or give-up it's stored heat quickly (a good heat transfer coefficient).
- weighs as little as possible and is as compact as possible - w.r.t. the energy stored.
- can evenly spread the absorbed heat throughout, ie. not a solid.

The reason Molten Salt is so suitable is it is a newbielink:http://en.wikipedia.org/wiki/Phase-change_material [nonactive] that uses the newbielink:http://en.wikipedia.org/wiki/Latent_heat [nonactive] effect to store far more thermal energy per kilogram than the same weight of some medium that does not change state. The best P.C.M.s in most cases are those that go from solid to liquid due the expansion of gases being an practical limitation.

Thank ewe very much Peppercorn. Yes...I understand now....I have one of those PCM packs for use as a heat pack....and then I have to boil the thing to get it back to a liquid.

Thank you very much for your explanation !....Presumably molten salt is not just molten salt ?...in other words..are there other chemicals added to achieve this reaction ?

Too bad the Gemasolar power plant is using sensible heat storage and not latent heat storage. There is no phase-change occurring in these salts. Thermal expansion would destroy the storage tanks and the thermal conductivity for a Na/K nitrate salt is much to low for the heat to be efficiently utilized during a phase-change. We are still many years off from utilizing phase-change materials in large, utility-scale electricity production. But the comments about using alloys, Zn, or other salts or encapsulated phase-change materials are worth investigating!
 

Offline peppercorn

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Why Channel Energy Into Molten Salt ?
« Reply #26 on: 13/10/2011 18:29:54 »
Too bad the Gemasolar power plant is using sensible heat storage and not latent heat storage. There is no phase-change occurring in these salts. Thermal expansion would destroy the storage tanks and the thermal conductivity for a Na/K nitrate salt is much to low for the heat to be efficiently utilized during a phase-change. We are still many years off from utilizing phase-change materials in large, utility-scale electricity production. But the comments about using alloys, Zn, or other salts or encapsulated phase-change materials are worth investigating!

Thanks for the info @jgchemie.
I didn't think the expansion would be that great for these salts, but for advantages to going to PCMs I would have thought the mechanical hurdles would have been overcome. Of course thermal conductivity is a genuine stumbling block if it is really too low.

Perhaps molten-zinc would be too expensive to scale-up to a system like this, but it appears that it might be useful on the more everyday, personal scale.
The sort of temperatures that it could allow could easily warrant the application of an Organic_Rankine_Cycle.
 

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Why Channel Energy Into Molten Salt ?
« Reply #26 on: 13/10/2011 18:29:54 »

 

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