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Emergency power for a fridge

Alex C

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Aug 11, 2020
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Hello!
I am living in Puerto Rico where we have to worry about power outages every year. I would like to eventually switch the whole house to solar but to begin with, I want to put together something simple mostly to power our fridge when we lose power. I believe the frdge has a load amperage of 6.5 A (I could be mistaken). Would a 12 volt system be enough power or should I try to go for a 24 volt? Appreciate any advice!
 
12 or 24V would be suitable for just the load the fridge will be putting on the system. If you plan on running the whole house 24V would be the better choice. What you need to do is work out how much power (watt hours) the fridge uses over the typical time your mains is out. You can do this with a watt meter. (example only purchase one suitable for your country). Once you know that you can size your battery etc.

Once you have that watt meter you can use it to determine your household's overall draw too and then size your whole system. Depending on your peak load (ie, how much you draw worst case, cooking dinner + aircon + hair drier etc etc) you may find that 24V isn't ideal and a 48V system becomes more appropriate. 24V will likely do it, but your DC cabling may get pretty hefty.
 
Another method is if your fridge has a yellow sticker indicating annual power usage. Divide that by 365, and you have your daily usage. A typical large residential fridge uses about 2kWh per day. The more efficient ones can use less.

Agree with gnubie, 24V would be better for future expansion.

Assuming 2kWh/day, you need 600W of solar to produce that daily and 4kWh worth of FLA/AGM (lead) batteries (4000/24 = 170Ah) for 24 hours with no sun.
 
I have a van with 400 w panels, 600ah battery, 2000 w inverter. My power was out almost three days. I parked the van near window and used hd extension cord to run my fridge and a small light. I was a little shaky after first day, but sun rise came and we were good.
 
I have a van with 400 w panels, 600ah battery, 2000 w inverter. My power was out almost three days. I parked the van near window and used hd extension cord to run my fridge and a small light. I was a little shaky after first day, but sun rise came and we were good.

Looks very interesting. Do you have an image of it?
 
Sitting in the dark with the frig running won't be much fun, so I would plan on a system that would power the frig, some lights, and a TV. I'd call that 2.0 to 2.5 kwh per day. You could put something together with four golf-cart batteries to give you ~5.0kwh of storage at 24V. Assuming you don't want to deplete the batteries more than 50%, that gives you 2500WH of power. Two or three 250W grid-tie panels would be enough to keep a system like that fully charged.

One important planning question would be your days of autonomy? That is, from the time your power goes off, till the time you have bright sunny weather, is about how long? Say a storm blows in on Monday afternoon, and that's when the power goes off. Will there be clear skies on Tuesday to start charging, or two days, or three? You'll have to scale your battery capacity up by how many days you'll need to supply how many watts, before the batteries get charged again. As a rule of thumb, I would have the number of panels to completely charge your depleted bank in one day of clear, sunny weather.
 
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