Quote:
Originally Posted by MN Renovator
With my defrost cycle disabled and the house kept at my winter temperature, my fridge uses about 1kwh per day if I never open the door during that day. I'd figure you want some wiggle room. Also don't forget you'll get a couple cloudy days in a row, you really need something automatic to switch back to the grid when your battery pack gets low or you'll be throwing away food if you make a mistake on sun estimates or how much battery you thought you had left. If you want to treat your batteries nicely(especially if going lead-acid) you need to size the system for very shallow cycles and plan for the cloudy days, also plan for the days you actually open and use the fridge, hot days of the year, and the ~300wh defrost cycles. I'd seriously consider oversizing to figure 2kwh per day unless you've got better than just energy star type stuff. You'll be spending more money on lead-acid and the solar PV modules than you'll probably ever save by running the fridge. You'd probably want to make the system big enough to power other things and then on days that aren't so sunny, scale it back down to the fridge.
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Modify the (standalone) freezer by adding a relay *after* the thermostat to run the compressor from solar power once the batteries reach full charge (or a little before), then switch back when the charge goes back down a little. Then it can only get colder than the thermostat setting. You'll also want to add a delay on break timer to avoid accidental short cycling.
That trick won't work for a refrigerator since it would freeze items you don't want frozen. But if you have a refrigerator dedicated to stuff that must be served cold but keeps fine at room temperature (water, beer, soda, etc.), you can indeed run it only during the day.