Heat storage in sand

[ojal]

we can't answer your question, "sand" doesn't mean anything.

On the other hand, your need is poorly defined; how many kWh do you want to store and with what temperature difference?

Even damp garden soil could make you happy between 0 and 100°C...

I find the words a little harsh and brittle?
In fact, for the moment I have not defined a specific need, I just launched a discussion on heat storage in sand because I was surprised not to see this subject already covered.
And this discussion can be used to define the types of uses that could be appropriate, the advantages and disadvantages of this type of storage, the projects in progress or already carried out, etc.
If there is a need to classify different sands, then it may or may not be wise to better define what we call 'sand'. And maybe any sand can be used, that's precisely the point of this kind of discussion.

[sicetaitsimple]

In fact, for the moment I have not defined a precise need,

This is the problem (already said above). A “good” solution is defined in relation to an objective!

[ojal]

In fact, for the moment I have not defined a precise need,

This is the problem (already said above). A “good” solution is defined in relation to an objective!

Why see problems where there are only discussions allowing a subject to be addressed globally?
We can try to define precise and well-defined uses.
Initially, the idea is to approach the subject of heat storage in sand in the most global way possible and to perhaps find judicious applications for it.

[Remundo]

roughly speaking, the thermal capacity of rocks varies relatively little between 2 and 3 MJ/m3/°C

thermal conductivity can be very variable depending on their nature and the humidity they contain.

Likewise, the density can vary greatly, between solid rock and decompacted sand, or even freshly deposited gravel.

here is a good summary table which gives you the 2 parameters
https://energieplus-lesite.be/donnees/e ... -des-sols/

you can see for yourself the versatility of sand depending on the water it contains.

That’s why I told you “sand doesn’t mean anything”.

And what's more, your needs are undefined, it's difficult to go further.

[Christophe]

And liquid water is at 4.18 MJ/m3/C° and it does not present the heat exchange concerns of a solid...

So if I may (I have a little experience on the subject...): sand as thermal storage at low temperature (residential, max temp < 100°C) has absolutely no advantage compared to liquid water: it is more expensive per kWh stored, less suitable for heat exchange and it is even more voluminous per kWh stored...

ps: reminder, 1 kWh = 3.6 MJ...1 m3 of sand does not even contain 1 kWh per degree...

[Remundo]

for those who want to "dig", if I dare say...

HEAT STORAGE IN COMPACT SOILS

whose conclusion is

The effect of water content, dry density and temperature on
the thermal parameters are studied on four compacted soils. The results
show that the conductivity, heat capacity and diffusivity of materials
reach a maximum around the Proctor optimum. The increase in the
temperature causes a slight increase in thermal parameters.

4. Conclusion
The coupled effect of water content, density and temperature variation
on the thermal parameters of soils were studied. The results show that
in the loamy soils studied, the conductivity and diffusivity increase up to
reach a maximum value around the Proctor optimum, then it
decreases on the wet side of the compaction curve. Thermal capacity
increases on the dry side of the compaction curve until reaching a plateau in
exceeding the Proctor optimum. The addition of sand made it possible to increase the density and
to improve the thermal parameters of the soil. The temperature variation between
20 and 50°C causes a slight increase in thermal parameters. The effect of
temperature on thermal conductivity and thermal diffusivity is reversible
after application of thermal cycles.
Soils compacted on the moist side of the Proctor optimum have good ability
to store heat: maximum thermal capacity and thermal conductivity
optimal ensuring good exchange between the soil and the geo-structure

Here we are at a low temperature (no more than 100°C), the water remains liquid at atmospheric pressure.

[ojal]

If I understand correctly, there is no real point in using sand if we stay at temperatures below 100°C, since in this case, a liquid like water seems to have more advantages.
The interesting applications to find would therefore be at higher temperatures, which is why I mentioned temperatures of the order of a few hundred degrees, for example 500°C...
And to rise to these temperatures in the context of domestic applications, the use of electrical resistances powered by solar panels is an option that seems to make sense to me?

[sicetaitsimple]

Is the use of electrical resistances powered by solar panels a path that seems to make sense to me?

It certainly exists (industrial ovens, etc.) but certainly not for 10€ at Casto.

[ojal]

Is the use of electrical resistances powered by solar panels a path that seems to make sense to me?

It certainly exists (industrial ovens, etc.) but certainly not for 10€ at Casto.

I have often seen hotplates equipped with spiral-shaped electrical resistances rise very high in temperature because the metal turns red.
These are indeed resistors that cost around ten euros

Electrical resistance temperatures spirale.png (214.11 KB) Viewed 896 times

Electrical resistance spiral.png (262.16 KB) Viewed 896 times

[sicetaitsimple]

Must try! immerse one in sand and plug it in, at least it will validate (or not) your concept. And if you can instrument with a thermometer measuring the temperature of the sand, it will be even better!