Phase change materials: storing solar heat

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Christophe
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Phase change materials: storing solar heat




by Christophe » 23/11/11, 14:07

Summary message on thermal storage in phase change materials (making it possible to multiply the energy density density of the storage and to obtain an interesting level of change of state) taken from https://www.econologie.com/forums/stockage-d ... 10905.html

dedeleco wrote:You can store thermal energy in quite a lot of body like hydrated and dehydrated salt and phase changes:
with commercial realization:
http://www.climatewell.com/index.html#/ ... w-it-works
and even make an ecolo cllimatizer:
http://www.climatewell.com/index.html#/ ... w-it-works

The lime stores 0,32KWh / kg of CaO (ie 320KWh / m3 but 900 ° C of concentrated solar energy is required.
Gypsum or plaster stores much less, but at lower T 163 ° C !!
sea ​​salt too.
Calcium chloride too.
http://fred.elie.free.fr/chlorure_calcium.htm
The number of bodies storing energy as well is huge with all the possibilities and temperatures.
http://en.wikipedia.org/wiki/Hydrate
http://scienceamusante.net/wiki/index.p ... de_chaleur
A list of real possibilities:
http://fr.wikipedia.org/wiki/Mat%C3%A9r ... ermique%29
http://en.wikipedia.org/wiki/Phase_Change_Material
At human temperature less than 100 ° C is stored at max 70 at 100 KWh / m3

The earth (clay, rock, etc.) free under our feet at + 36 ° C above the ambient stores 10KWh / m3 (between 20 ° C and 56 ° C).

Paraffin at 60 ° C 60KWh / m3 approximately (dodecanoid).

Overall view of the capacity possibilities 0,1KWh / L = 100KWh / m3 depending on the temperature:
http://www.bine.info/hauptnavigation/pu ... el=1436%29
Image


A solar power plant with molten salts is presented in this report: https://www.econologie.com/la-4ieme-revo ... -4370.html
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by chatelot16 » 23/11/11, 14:28

it is not easy to compare stored energy with phase change and water alone

with a phase change the storage is done at a precise temperature, all the calculated energy is recovered at almost the same temperature

With water or land, the amount of stored energy is proportional to the stored temperature difference ... With a large temperature difference, we can store as much energy in water as in a salt change of phase, except that because of this great variation of temperature it is usable only with a heat pump in complement ... to the extreme of reasoning we let the sun and the earth do what it want and use what has been naturally stored by a geothermal heat pump

in your table to find a figure as low for water it is calculated with a temperature variation too low

then we must not count that the energy per liter of matter: it is rather necessary to count the energy stoké by euro of material invests / I find that the water is the cheapest, even the water tank is cheaper that way to use the bizare salt

moreover the water of the thermal reservoir can be used directly of thermal fluid and to avoid the exchanger

I do not say that to divert the debate: it will be here the debate on the change of phase, but to compare with other means
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by dedeleco » 23/11/11, 14:47

The free land in situ is still much cheaper than the water tank dear to Christophe!

Between seasons the conservation of this heat on 4 months in a tank is not obvious more !!!

So all the financial balance sheet: house and storage, many possible variants to do : between store a lot with not very insulated house or store little but isolating very strong very tight like a dewar !!

All this not to invest by paying 50 to 100 years of usual heating !!!
As Christophe says, who with this argument would never have built the remarkable house, that he bought !!!
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by Christophe » 23/11/11, 14:48

It depends on the material and the desired temperature ranges!

The higher the "change of state" T °, ​​the more potential thermal energy is stored, but the more losses there will be in storage ...

In short I think that each MCP must be adapted to the use: we use salts in the thermosolar plants because we need high temperatures.

In the domestic it is very different.

For example with palm oil (probably the cheapest MCP) and 1 / 4 the volume of the water buffer, we win between 50 ° and 42 ° C (assuming the bearing at 42 ° C): 2.2 times energy compared to water alone ... Detailed calculation here: https://www.econologie.com/forums/stocker-de ... t7421.html

Gold 42 ° C is precisely the ideal temperature for heated floors: neither too hot (losses) nor too cold ...
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by Gaston » 23/11/11, 14:54

chatelot16 wrote:in your table to find a figure as low for water it is calculated with a temperature variation too low
Given the position of the point about water, I think it is the change of phase water / ice ...
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by dedeleco » 23/11/11, 15:05

I think it is the change of phase water / ice ..

very clear and obvious because stack on 0 ° C !!
and the water heating water (variation of 50 ° C between 20 ° C and 70 ° C) is less, with 55 KWh / m3
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by Christophe » 23/11/11, 15:06

Absolutely, I had not seen the remark!

Where would the point for the steam? : Cheesy:

In fact at the rate of 330 kJ / kg of melted ice, we are good on the graph but for the evaporation we are at 2200 kj / Kg, so far beyond the ordinate scale ...

: Idea:

Schmelz = fusion so CQFD
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by chatelot16 » 23/11/11, 17:49

the change of phase water vapor is of no interest because it would be necessary to store the steam to conserve the energy!

there are only solid liquid changes that are interresting
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by dedeleco » 23/11/11, 18:54

Steam should be stored

Compressed at high pressure to more than 300 ° C, deep underground, like volcanoes and only waiting to explode in the super-volcanoes, when the magma rises and releases its water vapor with colossal energy (see the volcano Toba 75000 years ago with a diameter of more than 100km of vaporized earth !!!
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by Christophe » 23/11/11, 19:40

chatelot16 wrote:the change of phase water vapor is of no interest because it would be necessary to store the steam to conserve the energy!

there are only solid liquid changes that are interresting


No interest no. But more difficult to store than other phases is on! The pressure would pose more technological problems than the insulation ...

Some urban heating networks are on steam in the USA ... for example in New York! (hence the smoking manholes in the films ...) But the steam is only "stored" for the time of transport ...
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