Help with a solar project.

[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.