Help with a solar project.

[th3w01f]

On an industrial scale, cold storage is considered one of the few *real* ways to store energy, in the sense that you can run the compressor balls-out during times of peak generation (lowest cost, in my world), and the "excess cold" carries forward to the times when the compressor isn't running. I don't know about the cooling ranges achievable with home systems, or the quality of insulation, but you might be able to tweak your thermostat to make the whole rig battery-free.

I'm going to have to sober up before completely digesting this one.

[Not_A_Llama]

I'm going to have to sober up before completely digesting this one.

When you have power (daytime), run the compressor past its usual cutoff point, which is usually around 0F. R134a boils at -15F, so maybe somewhere around there. The extra 15 degrees is a thermal buffer that acts like a battery. Maybe enough to make the system run battery-less. If you keep the freezer mostly full (water/ice bottles?), your opening losses will be minimal and you'll have crazy good heat capacity.

Aw hell, let's get nerdy:
Specific Heat of Water Ice in the range of -15 to -25C is ~= 1.94 kJ/kgK

Let's say you have a 15 cubic foot chest freezer that's packed 70% full of frozen items that I'll model as ice. In the extra 15F you get by running the compressor past the usual 0F cutoff to -15F, you have effectively stored...
specific heat * capacity of freezer * density of water * pack density of fridge
1.94 kJ/kgK * 15 cubic feet * (1 g/cm^3) * 70% * 9 kelvin = 1.4 kWh
(and the fun google query that calculates it, if you wanna do it with specific numbers)

So effectively, just running it down to -15F in a mostly-packed fridge, you get a free day of energy storage (well; so long as the freezer is efficient enough to keep the cold in, during the heat, and as you're opening and closing). Realistically, you have about double that before you hit 32F, and then even more as the 32F stuff starts melting.

So that's an idea.

[DFBrews]

When you have power (daytime), run the compressor past its usual cutoff point, which is usually around 0F. R134a boils at -15F, so maybe somewhere around there. The extra 15 degrees is a thermal buffer that acts like a battery. Maybe enough to make the system run battery-less. If you keep the freezer mostly full (water/ice bottles?), your opening losses will be minimal and you'll have crazy good heat capacity.

My chest freezer cuts out at -10 I did a PID controller to bypass the factory thermostat and program it to avoid short cycling. I run my lagering chamber for home brewing this way I have a tub of glycol a pump and then a heat exhxanger in a separate box where i keep the beer

[Not_A_Llama]

My chest freezer cuts out at -10 I did a PID controller to bypass the factory thermostat and program it to avoid short cycling. I run my lagering chamber for home brewing this way I have a tub of glycol a pump and then a heat exhxanger in a separate box where i keep the beer

Cool, let's rejigger my calculations, then..
1.94 kJ/kgK * 15 cubic feet * (1 g/cm^3) * 70% * 5 kelvin = 0.8 kWh

So it's less rosy here. A lot depends now on real-life performance - can your freezer keep a load of -10F goods below 0F in a 24 hour span? If so, you're probably good battery-less. If not, you're still discounting your battery installation.

Assuming your 6V figure from before, that's 800 Watt*hours / 6 volts = 133 Amp Hours of battery. Half and a bit of battery.

Edit: Mother of god. I have created the ultimate unit mixing disaster. Begone, google calculator! Look on my works, ye mighty, and despair!