What size solar system to run a refrigerator for backup if grid went down?

My fridge runs at 115 v at 3.3 amps and 380 watts . How many batteries and solar panels would you recommend ? Best inverter if I want to grow the system ?
Estimate on running a week with no grid . Location is Alabama.

bridges1 said:

My fridge runs at 115 v at 3.3 amps and 380 watts . How many batteries and solar panels would you recommend ? Best inverter if I want to grow the system ?
Estimate on running a week with no grid . Location is Alabama.

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Assuming the solar panels will charge the battery, on a good day, how many "bad sun" days does the battery need to carry the load?

If you have a 50% duty cycle that would be 12hrs x 380watts= 4560w. Per day. If you could get 6hrs of sun a day at 800watts that's 4800watts of replacement power.

You need to put a power recording meter like a $25 "Kil-o-watt" meter and get the power per day over a period of several days to see what the frig uses/needs. A larger inverter that allows some growth room will often cost power just from being on, where a smaller inverter will waste a little less. This is just the cost of the business. An 1000w inverter should work if the frigs is a modern one. I think the modern ones need less power to get started. NVS suggests it might take 800 watts of solar panels to make up for 24 hours of use at 50% on time. Consider that plus,
1. You need to be running while you are charging (without robbing your charge power) so add about 400 watts of panels for that load. Also, on a nice sunny day where the day is sun all day long, 6 hours of sun is a blessing. For normal days where some clouds are around or it is cloudy in the morning (Alabama has clouds, right?) it would be good to fully charge in 3 or 4 hours. So maybe 1500-2000w of panels would be in order. Consider you have two totally overcast, dark rainy days. My power is down to about 5% of a normal sunny day, so on those days, I count as zero. The third day, it clears off about midday and you want to fully charge that battery. If the battery can carry the load for 3 full days, 72 hours, now you want to make that up over just a few hours of good sun, if you don't know what tomorrow holds. This is where charging off a generator might make sense. When the weather just don't work, you can't really make a system big enough to run without real sun for 7 or 8 days for those really worst cases.

bridges1 said:

My fridge runs at 115 v at 3.3 amps and 380 watts . How many batteries and solar panels would you recommend ? Best inverter if I want to grow the system ?
Estimate on running a week with no grid . Location is Alabama.

Click to expand...

Will be using Lithium Batteries .

DThames said:

You need to put a power recording meter like a $25 "Kil-o-watt" meter and get the power per day over a period of several days to see what the frig uses/needs. A larger inverter that allows some growth room will often cost power just from being on, where a smaller inverter will waste a little less. This is just the cost of the business. An 1000w inverter should work if the frigs is a modern one. I think the modern ones need less power to get started. NVS suggests it might take 800 watts of solar panels to make up for 24 hours of use at 50% on time. Consider that plus,
1. You need to be running while you are charging (without robbing your charge power) so add about 400 watts of panels for that load. Also, on a nice sunny day where the day is sun all day long, 6 hours of sun is a blessing. For normal days where some clouds are around or it is cloudy in the morning (Alabama has clouds, right?) it would be good to fully charge in 3 or 4 hours. So maybe 1500-2000w of panels would be in order. Consider you have two totally overcast, dark rainy days. My power is down to about 5% of a normal sunny day, so on those days, I count as zero. The third day, it clears off about midday and you want to fully charge that battery. If the battery can carry the load for 3 full days, 72 hours, now you want to make that up over just a few hours of good sun, if you don't know what tomorrow holds. This is where charging off a generator might make sense. When the weather just don't work, you can't really make a system big enough to run without real sun for 7 or 8 days for those really worst cases.

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Thanks to all for the info. I will order a Kil-o-watt" meter today and get back. I have a 5000 watt generator and would like to use to charge the batteries for backup on cloudy days.

Is it realistic for you to be sitting there in the dark listening to the refrigerator run? Will you open the refrigerator door when you need light? What you really are going to need is a system that will power the frig, keep the lights on, and power the playstation so your kids do not drive you insane. Let's throw together some numbers as to what you need to get you through a crisis.

Refrigerator: 2500Wh/day
Lights; 100W X 4 hours/day: 400Wh
TV/console; 150W X 3 hours/day: 450Wh
Misc; laptop, phone, ect: 250Wh/day
Inverter on 24/7: 1000Wh/day

Added up, that's 4600Wh. Assuming you get 3 sunhours of power towards the winter, that's 4600Wh/3sh = 1533W of panels. Call that six 260W grid-tie panels. That will fit on just one double row array frame. With two days of autonomy, that would be a 18000Wh lead-acid battery, or a 12500Wh Li battery. At 24V that would be a 750Ah battery, vs a 520Ah Li battery. Cut these battery numbers in half if you go with 48V.

This is very doable, about the size of my workshop system, with 2000W of panels, a 4000W inverter, and a 568Ah battery at 24V. Adjust the numbers in the list to fit your real-world measurements. Math will stay the same.

MichaelK said:

Is it realistic for you to be sitting there in the dark listening to the refrigerator run? Will you open the refrigerator door when you need light? What you really are going to need is a system that will power the frig, keep the lights on, and power the playstation so your kids do not drive you insane. Let's throw together some numbers as to what you need to get you through a crisis.

Refrigerator: 2500Wh/day
Lights; 100W X 4 hours/day: 400Wh
TV/console; 150W X 3 hours/day: 450Wh
Misc; laptop, phone, ect: 250Wh/day
Inverter on 24/7: 1000Wh/day

Added up, that's 4600Wh. Assuming you get 3 sunhours of power towards the winter, that's 4600Wh/3sh = 1533W of panels. Call that six 260W grid-tie panels. That will fit on just one double row array frame. With two days of autonomy, that would be a 18000Wh lead-acid battery, or a 12500Wh Li battery. At 24V that would be a 750Ah battery, vs a 520Ah Li battery. Cut these battery numbers in half if you go with 48V.

This is very doable, about the size of my workshop system, with 2000W of panels, a 4000W inverter, and a 568Ah battery at 24V. Adjust the numbers in the list to fit your real-world measurements. Math will stay the same.

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Having a few lights is ok. My idea was to start a system that would run the fridge then as budget permitted add to the system. Can I do that for around $3500.00

You should look for "All in one" units. They can, charge battery from grid or generator, can charge from solar, can run off of the grid and auto-switch to battery/solar (U.P.S. mode) and some other tricks as well. The can be used with a number of battery types. 24v or 48v would be wise. 48v with a server rack type LiFePo4 battery would be worth considering. 24v might make sense is you plan to keep the system fairly small and want to assembly your own battery from cells, 8 cells for 24v and 16 cells for 48v.

Here is a link to some units. Do some research and ask questions before you decide. There are many decision points. The 3000watt size are pretty common and will carry your frig plus other things. Some items may not be UL listed and you might not be able to connect in a permanent way if you have local building codes you must comply with.

With a generator available you only need a battery large enough to carry you maybe 24-36 hours if you have cloudy days. On cloudy days (if it is not dark rainy type clouds) you can get 30-60% power depending on how bright the sky is. If you can get enough panels that...say 50% power can carry your load and not dig into the battery's charge, then you can have cloudy days that are somewhat neutral and catch up the following day with sun or generator. I have an emergency system that is sort of a hobby to play with, but really serious about being ready for a power outage as we have a large freezer that is full an other things that must run. I have more panels than I really need but I can sock the power to the battery in a few hours of the sun will shine. You have to find a balance on what you want to spend for batteries and for panels.

DThames said:

maybe 1500-2000w of panels

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I was thinking “800W would do it” so figured “1600W is what they need.”
So I’d go with that. That leaves headroom for lighting and

Refrigerators are great battery killers. You need more protection than just the 10.5V disconnect the inverter has. That isn't to save the battery, it is to keep the FET from being destroyed. In emergencies you need to change your habits and not just open the door all the time. Big battery systems always work. I find it amusing that I run a refrigerator, hot water for showers etc, dishwasher with heated dry, and a large capacity LG clothes washer with its own 40 gallon water tank with all cycles using hot water all from PV. And as night approaches the battery has to be fully charged to run some medical equipment to keep me alive. Even rain for a couple days doesn't bother me. I only have a car battery!