Convenient materials for storing heat ?

[Externet]

Hi. 

Surplus energy from solar panels has been heating water during the day in a non-sealed 200 litre (55 gallon) drum and used in winter as heating source during nightime.   What materials could store more energy instead of water, that along weeks diminishes level from steamy evaporation ?

Oils have a lower temperature coheficient but can be heated well to >200C;  perhaps yielding a greater Q = mCΔT

 If heating from electric elements in a oil container has lots of iron, or aluminium junk submerged, would it keep more heat ?   What simple common materials as rocks, glass?, polyethilene, metal junk in oil bath (or something else) -with no phase change complications- would you choose to implement to absorb and release more heat at winter nightimes ?

I see a surprising figure for pine wood at ---> http://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html

Edited August 20, 2023 by Externet

[exchemist]

3 hours ago, Externet said:

Hi. 

Surplus energy from solar panels has been heating water during the day in a non-sealed 200 litre (55 gallon) drum and used in winter as heating source during nightime.   What materials could store more energy instead of water, that along weeks diminishes level from steamy evaporation ?

Oils have a lower temperature coheficient but can be heated well to >200C;  perhaps yielding a greater Q = mCΔT

 If heating from electric elements in a oil container has lots of iron, or aluminium junk submerged, would it keep more heat ?   What simple common materials as rocks, glass?, polyethilene, metal junk in oil bath (or something else) -with no phase change complications- would you choose to implement to absorb and release more heat at winter nightimes ?

I see a surprising figure for pine wood at ---> http://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html

The evaporation issue can be fixed by the simple expedient of closing the container, provided a suitable expansion vent is incorporated, as in any domestic heating system. 
 

Water has a high specific heat, so can absorb a lot of heat with only modest rise in temperature. You will struggle to find many readily available materials with a higher specific heat than this. If you use oil you will get a higher temperature for a given amount of heat stored, because its specific heat is lower. At what temperature do you want the stored heat to be delivered?

[Externet]

Thanks.  

Yes, tables show water with no 'competitors' in specific heat for common available materials.   A "suitable expansion vent"  is not a 'closed container'   Pressure builds up, vapor leaks out; same thing.  How can be made it to work better being both 'closed' and 'vented' ?

[exchemist]

41 minutes ago, Externet said:

Thanks.  

Yes, tables show water with no 'competitors' in specific heat for common available materials.   A "suitable expansion vent"  is not a 'closed container'   Pressure builds up, vapor leaks out; same thing.  How can be made it to work better being both 'closed' and 'vented' ?

The vent in a central heating system involves a long pipe up with a U shape at the top. The hot water does not percolate up this pipe, so the water surface exposed to the atmosphere is at ambient. It is also a very small surface. Combining these factors, the evaporative loss from it will be practically nil. You can reduce it even more by arranging the vent to come from the bottom of the vessel, where the coldest water is. The only important thing is that there is a vent, so that expansion can be accommodated without stressing the vessel.  

[Externet]

Thank you; understood.

[John Cuthber]

Or you can use a non-rigid container, for example, bellows- and not worry about the expansion/ contraction.
You really can't beat water for heat capacity.
In the other hand, if you allow phase changes, you can do even better.

https://en.wikipedia.org/wiki/Sodium_sulfate#Heat_storage

[exchemist]

10 hours ago, John Cuthber said:

Or you can use a non-rigid container, for example, bellows- and not worry about the expansion/ contraction.
You really can't beat water for heat capacity.
In the other hand, if you allow phase changes, you can do even better.

https://en.wikipedia.org/wiki/Sodium_sulfate#Heat_storage

That’s interesting. Mind you, 32C is not very warm for a heater. Though I suppose you could use with a heat pump to jack it up to 50C or so.

[Ghideon]

On 8/20/2023 at 12:50 PM, Externet said:

How can be made it to work better being both 'closed' and 'vented' ?

Here is the solution in my current house, it has a standard closed heating system. There is a tank with a pressurised bladder which allows for expansion: 

 

The pressure can be adjusted by adding air through a valve and/or by adding water to the closed system.
Valve for adding air:

Any overpressure is vented through an emergency valve (see top picture)

[Steve81]

See this:

https://en.m.wikipedia.org/wiki/Solar_power_tower

Early designs used these focused rays to heat water and used the resulting steam to power a turbine. Newer designs using liquid sodium have been demonstrated, and systems using molten salts (40% potassium nitrate, 60% sodium nitrate) as the working fluids are now in operation. These working fluids have high heat capacity, which can be used to store the energy before using it to boil water to drive turbines. These designs also allow power to be generated when the sun is not shining.