A small example of worthwhile forward planning

[openspaceman]

Sorry OSM missed that one! The freezer out here goes down to minus 16. I am also planning for a chest freezer in the cabin back in Scotland so it is all circling in my head.

When we had less battery storage I timed the freezer to go off through the night and kick back in when the odds favoured the likelihood of PV generation. Another minor timeshifting of power use and preserving that battery soc to the morning. I could see something similar in a chest freezer but with the added lift of the brine blocks being started in Solar days until solid and the freezer being off through the night and kicking in at 10am?

Bear in mind my physics knowledge dates back to the 1960s but a it should be possible to tune the brine to the temperature you wish it to start freezing at but as it freezes the remaining solution will become more concentrated and hence freeze at a lower temperature, the liquid will still be storing some coolth though.

Seems I can't look at anything anymore without thinking of timeshifting energy use.

Yes me too, I wish I could add more insulation to my DHW tank but no space, so the battery must bear the brunt of it.

[Stinsy]

I posted "I will be watching the result too but to get to 0 Fahrenheit I think you will need 26% salt by weight.

So I think you need to dissolve 310 grams of salt in 1.5 litres of water."

0 Fahrenheit was chosen by Fahrenheit because it was the coldest he could get I think, it's about -19C which is and ideal point for a freezer to toggle around but there has to be enough heat exchange surface for it to melt overnight from the heat getting into the freezer from outside as the delta T is only a a small change in temperature for the heat of fusion to be taken up between solid and liquid.

If the freezer is super insulated and not opened then it may not warm up enough to melt the brine, OTOH from looking at my overnight battery consumption it looks like my freezer comes on about 5 times for about an hour between midnight and 08:00.

Depends what your objective is!

If it is to use excess solar in the day and give it back at night (as was my aim) then I think the experiment was a failure. It took 2 days for the jug to melt in the fridge!

However if the aim is to help the freezer stay cold in a power outage (which I believe is Joe's aim) then I'm more hopeful. The jug giving off it's stored phase-change energy over 48hrs (or whatever) is in fact better in this case.

[AE-NMidlands]

Depends what your objective is!

If it is to use excess solar in the day and give it back at night (as was my aim) then I think the experiment was a failure. It took 2 days for the jug to melt in the fridge!

A) try using a metal (stainless?) jug and
B) try copper busbar-size conductors dipped in it as heat-sinks/ transfer bars. copper tube even. Lacquer (as used on transformer windings) might protect them from the brine...

[Joeboy]

Depends what your objective is!

If it is to use excess solar in the day and give it back at night (as was my aim) then I think the experiment was a failure. It took 2 days for the jug to melt in the fridge!

A) try using a metal (stainless?) jug and
B) try copper busbar-size conductors dipped in it as heat-sinks/ transfer bars. copper tube even. Lacquer (as used on transformer windings) might protect them from the brine...

Personally, I need to dial this back to 'nugget' territory which co-incidentally is where my brain lives on a daily basis.My vague understanding of this process is that brine gives up more heat than standard water due to the magic pixies inherent in salt. Freeze that liquid down to the max your freezer can go to and you will have a significant advantage over a standard water ice cube icebox scenario?
Timing(weight of salt) the mix means you can have a bottom layer of tupperware boxes full of brine that will keep the freezer cold when power is off and not melt in a standard non grid trip out 24 hr cycle. The energy used to keep the brine frozen can be dialed around to ensure it is being pulled back down to max freeze in Solar hours thus saving battery soc or likelihood of grid touch. Plus the bottom layer will remain solid. But it's all about the magic salt pixies really.

[Stinsy]

Depends what your objective is!

If it is to use excess solar in the day and give it back at night (as was my aim) then I think the experiment was a failure. It took 2 days for the jug to melt in the fridge!

A) try using a metal (stainless?) jug and
B) try copper busbar-size conductors dipped in it as heat-sinks/ transfer bars. copper tube even. Lacquer (as used on transformer windings) might protect them from the brine...

Personally, I need to dial this back to 'nugget' territory which co-incidentally is where my brain lives on a daily basis.My vague understanding of this process is that brine gives up more heat than standard water due to the magic pixies inherent in salt. Freeze that liquid down to the max your freezer can go to and you will have a significant advantage over a standard water ice cube icebox scenario?
Timing(weight of salt) the mix means you can have a bottom layer of tupperware boxes full of brine that will keep the freezer cold when power is off and not melt in a standard non grid trip out 24 hr cycle. The energy used to keep the brine frozen can be dialed around to ensure it is being pulled back down to max freeze in Solar hours thus saving battery soc or likelihood of grid touch. Plus the bottom layer will remain solid. But it's all about the magic salt pixies really.

The point is: there is a huuuuge amount of energy stored in the phase change.

So: ordinary water chilled to 2℃ will cool a room down by a teeny bit as it warms up to room temperature. However chill it to -2℃ (and freeze it solid) then it stores many times as much energy cooling a room by a much more substantial amount as it raises to room temperature.

The point of the brine is that the melting point of pure water is too high to be useful in a freezer. A block of normal ice will keep a fridge cool for an extended period (because it absorbs heat while it is melting), a freezer: notsomuch.

However if we brine-up our water, we lower the melting temperature substantially. This then becomes useful in a freezer because the melting brine will absorb heat not at temperatures above 0℃ but at temperatures above -19℃ therefore keeping your food frozen...

[AE-NMidlands]

I'm starting to understand...
Although a salt solution has a lower SH than water (due to the salt displacing the water super-molecules) in fact you push the water phase change down to a useful freezer temperature.
I think I have got it now... I read previous posts as saying that the salt crystals coming out of the brine was the phase change being exploited.
(Apart from some strange compounds like CaCl2 and NaOH I had never encountered any latent heat associated with dissolution or solutes crystallising out..)
A

[Oldgreybeard]

I'm starting to understand...
Although a salt solution has a lower SH than water (due to the salt displacing the water super-molecules) in fact you push the water phase change down to a useful freezer temperature.
I think I have got it now... I read previous posts as saying that the salt crystals coming out of the brine was the phase change being exploited.
(Apart from some strange compounds like CaCl2 and NaOH I had never encountered any latent heat associated with dissolution or solutes crystallising out..)
A

Our hot water heat storage is provided via a bit of kit that exploits the big gain in stored energy that you can get from changing the phase of a material. It uses sodium acetate, the stuff used in hand warmers that are charged by putting them in boiling water and triggered to discharge and give out heat by a small "clicker" inside the gel capsule. There's some secret source in the box that enables nucleation to be triggered automagically and to stop automatically as well. The result is a box that's pretty small but which stores as much heat as a ~210 litre water tank.

Best bit about it is that the heat losses are tiny. We went away for a week, with the thing switched off (for safety), came back and found we still had a "tank" of hot water as the thing had just sat there with the sodium acetate in liquid form and was only triggered to start turning back into a solid when we ran off some hot water when we got home.

[Stinsy]

I'm starting to understand...
Although a salt solution has a lower SH than water (due to the salt displacing the water super-molecules) in fact you push the water phase change down to a useful freezer temperature.
I think I have got it now... I read previous posts as saying that the salt crystals coming out of the brine was the phase change being exploited.
(Apart from some strange compounds like CaCl2 and NaOH I had never encountered any latent heat associated with dissolution or solutes crystallising out..)
A

Our hot water heat storage is provided via a bit of kit that exploits the big gain in stored energy that you can get from changing the phase of a material. It uses sodium acetate, the stuff used in hand warmers that are charged by putting them in boiling water and triggered to discharge and give out heat by a small "clicker" inside the gel capsule. There's some secret source in the box that enables nucleation to be triggered automagically and to stop automatically as well. The result is a box that's pretty small but which stores as much heat as a ~210 litre water tank.

Best bit about it is that the heat losses are tiny. We went away for a week, with the thing switched off (for safety), came back and found we still had a "tank" of hot water as the thing had just sat there with the sodium acetate in liquid form and was only triggered to start turning back into a solid when we ran off some hot water when we got home.

What is the make/model of your heat storage thingy?

[openspaceman]

I read previous posts as saying that the salt crystals coming out of the brine was the phase change being exploited.
(Apart from some strange compounds like CaCl2 and NaOH I had never encountered any latent heat associated with dissolution or solutes crystallising out..)

That was probably because I complicated things by saying the salt came out of solution. As I understand it when the brine turns to ice the ice is just water, the salt precipitates if the solution was saturated.

Perhaps someone trying this can extract a lump of the ice out of the brine, wash it in fresh water then sample it.

[openspaceman]

What I forgot to say is I order haggis and smoked salmon from Scotland which arrives next day by courier. The box is lined with that reflective multilayer insulation but inside with the meat are gel packs (heat sealed bags) of water and a polymer that has a lower freezing point, they arrive still fairly solid. If I order more I shall try and see what temperature they freeze at but in other respects they would be fine in a freezer.