Dedicated Backup

DCC

New Member
It's not uncommon for me to lose power a few days a year due to weather related events. While this is not usually a big problem, I was considering a solar panel and battery system just to run my refrigerator, so at least my food would not spoil during those outages. I was thinking the simplest solution would be to just run the refrigerator from the battery full time, rather than needing some system to switch between the grid and battery. Assuming the average requirement for a refrigerator is 150 watts, isn't that 1800 watt / hours per day? Assuming battery to provide that 24 hours per day would need to make be a 150 amp hours available per day. Assuming a 100 panel provides 300 watt hours per day, it would take 6 100 watt panels to run that refrigerator 24 hours per day. Of course, this is not considering efficiency loss or compensating for overcast days, but just taking these number, there must be something very wrong, because I have seen many RV channels powering a refrigerator and more with much less solar capability. These numbers come from a quick google search but can someone tell me where the error is and a realistic way to calculate those needs?
 
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snoobler

Solar Honey Badger
Welcome to the forum.

A kill-a-watt meter can report the actual kWh used. Typical residential fridge is around 2-2.5kWh/day.

Your RV fridge information is either inaccurate, misinterpreted or context-specific that doesn't apply in all cases.

RV fridges are a different beast. If you're talking about an AC/Propane absorption fridge, a 7.6cu-ft unit can consume up to 5kWh/day. It takes 5-6X more energy to power an RV fridge than compressor-type. If they replace that absorption fridge with a 10cu-ft high efficiency compressor-type fridge that fits in the same space, or if they replace the cooling unit with a 12V one, then they can get consumption below 1kWh/day.

Running a "standard" RV fridge off electric is a massive demand.

Your approach to solar panels needed is correct. Divide kWh needed by the number of solar hours for your location/climate, and that's the panel wattage needed. You will of course need a comparable amount of kWh of batteries if you want to continue running through the night.
 

DCC

New Member
Welcome to the forum.

A kill-a-watt meter can report the actual kWh used. Typical residential fridge is around 2-2.5kWh/day.

Your RV fridge information is either inaccurate, misinterpreted or context-specific that doesn't apply in all cases.

RV fridges are a different beast. If you're talking about an AC/Propane absorption fridge, a 7.6cu-ft unit can consume up to 5kWh/day. It takes 5-6X more energy to power an RV fridge than compressor-type. If they replace that absorption fridge with a 10cu-ft high efficiency compressor-type fridge that fits in the same space, or if they replace the cooling unit with a 12V one, then they can get consumption below 1kWh/day.

Running a "standard" RV fridge off electric is a massive demand.

Your approach to solar panels needed is correct. Divide kWh needed by the number of solar hours for your location/climate, and that's the panel wattage needed. You will of course need a comparable amount of kWh of batteries if you want to continue running through the night.
I was using an average of 150 watts but looking up my specific model, it is rated at 451kw/h per year which would be about 1236w/h per day. You are probably right about me not understanding the context of the RVers as they may plug in or use a generator in addition to the solar. I'm only trying to determine if that plan is even practical so accurate numbers are not really needed at this point. Even so, the rough calculations make me think a better and cheaper solution would be just to have a 2~3 day battery backup charged by the grid. Of course that wouldn't work if the grid was down beyond that but in those situations keeping the refrigerator running may not be the priority.
 
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OffGridInTheCity

Solar Addict
I was using an average of 150 watts but looking up my specific model, it is rated at 451kw/h per year which would be about 1236w/h per day. You are probably right about me not understanding the context of the RVers as they may plug in or use a generator in addition to the solar. I'm only trying to determine if that plan is even practical so accurate numbers are not really needed at this point. Even so, the rough calculations make me think a better and cheaper solution would be just to have a 2~3 day battery backup charged by the grid. Of course that wouldn't work if the grid was down beyond that but in those situations keeping the refrigerator running may not be the priority.
You're numbers are not that far off. My full-size kenmore refrigerator uses <2kwh/day. If the goal is just to run the refrigerator (for a few days) in a power outage - you go with a UPS type solution instead of full solar. A modest UPS (such as an APC UPS) could be easily fitted with a battery large enough to run the refrigerator a few days and is made to be in-the-circuit 24/7 and topped off by grid - e.g. pretty simple / not much maintenance. There are also solar generators that have UPS type functionality - but typically you don't leave them on 24/7 year after year - so you'd deploy it when the power went out.

Specifically - something like this - https://www.ebay.com/itm/2340437460...9wN%2FttFzK5Bw22qha5|ampid:PL_CLK|clp:2334524
would easily power the refrigerator. Inside is typically an Anderson connector... that you plug into lead-acid batteries that would last an hour. You could create a 24v external battery (maybe LifePo4 or whatever) large enough to provide 2kwh/day and just plug it in.
 
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