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Off Grid With Your Refrigerator, Complications, Details, Ideas (Read 7456 times)
Solar Freak
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Re: Off Grid With Your Refrigerator, Complications, Details, Ideas
Reply #1 - Jun 29th, 2013 at 9:43pm
Some times in the winter the sun dont shine for 4 or 5 days in a row in Oklahoma. So the panels would charge lot less. So figure maybe at least 6 or 235 watt panels because when the suns not so bright with clouds covering my panels can possibly make just 20 watts Cry or up to 100 watts or more even 300 watts for 3 panels on pretty cloudy day Cheesy. A lot of cloudy days in row would be trouble Cry so if you can afford a pallet of ten panels that would be best. Some people even get 20 panels or two pallets that would be pretty safe Grin.

Update on the Freezer 24 hour Killawatt Usage

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Off Grid With Your Refrigerator, Complications, Details, Ideas
Jun 28th, 2013 at 11:30am
If you are going to take your refrigerator off grid you will want to know what it draws on a daily basis so you can decide how many batteries you will need and what size inverter will power it.

My refrigerator pulls about 180W running, 300W surge at startup and 500W in defrost. It's 21 Cu Ft and a top freezer. No digital controls or anything. It has a simple defrost timer, uses a small motor to run the clock/timer. I put extra insulation on the back where I could.

It uses about 1,400 Wh a day in the winter, 1,800 Wh a day in the summer. Defrost happens about twice a day and is short, about 5 to 7 minutes, so it's only about 40 Wh each run but that's when you pull the most power.

This was all measured over time with a Kill-A-Watt meter, get one if you don't have one, it's a must for going off grid.

It runs really good from a pure sine wave inverter, either a 600W one or a 1800W one I have and two of the big walmart marine deep cycle batteries at 114 Ah per battery.

The problem with a fridge is that it isn't a constant load, it cycles on and off at different times and you can't predict when defrost happens.

If you can get a timer that has several settings per day, you could have it turn off at night in a way that it only comes on a few times and that might save energy if your batteries are smaller but you have more than enough solar panels to cover it in the day.

There are a number of people who have modified a chest freezer to be a off grid refrigerator by modifying it's thermostat to click on and off at higher temperatures at around 38F to 42F.

The advantage of a off grid chest freezer as a refrigerator is that you don't lose any cool air when you open the door. Use google and you can find many articles and videos on the subject. If you do that you would start by plugging it into the grid and watching it for a number of days with a Kill-A-Watt meter to see how it does before deciding on what system to set up.

To monitor the temp on my fridge, I put the outdoor transmitter unit of a wireless indoor/outdoor digital thermometer inside the fridge and the receiver unit on the counter about 1 foot away. It works good even though you would think the metal would block the signal. It's the Accurite brand from walmart.

Once you know the daily watt hours it draws you can get an idea of the battery storage and panels you need.

In this case, and this is just an estimate that may need adjustment in the real situation, the solar panels will have to generate about 3,000 Wh a day, which would power the fridge and charge the batteries for use at night. Figure on 50% loss with the batteries, but remember it's only for the time when solar isn't generating.

You may also want to think about what happens on rainy dark days. Possibly some kind of back up generator, or wind turbine system, or more batteries so you can go days without solar power.

3,000 Wh a day / 24V = 125 Ah which is close to the 2 x 114 Ah batteries (24V in series so the amp hours do not add up, the volts go up). Of course you never draw that much out of your batteries, usually it's safe to use about half of that.

And we do use only 1/2 of that because in the daytime the solar panels are enough to power the fridge and charge the batteries, remember that the fridge cycles and so the batteries can charge between that. One cycle of the fridge in this case is only about 75 Wh (summer) so the batteries don't run down completely at each run and the batteries come back up to charge pretty quick after each run by noon or so, that's what you should try for on a good day.

How many watts of panels would you want? You can calculate that and get close by using about 8 hours of sun a day, and a need of 3,000 Wh / 8 = 375W all day long. You have losses in some of that so figure around a 500W set of panels would work well. Better to have more at the low prices of panels now it doesn't hurt. 2 x 235W panels = 470W and some wire loss would be just about right and at $1/W you could add one more panel for $235 and use the batteries for another small load.

You should try to go 24V with your system, it just works better and wire loss is less, amp draw is less, wire cost is less because it's smaller, fuses are less so it's just a lot better.

As you can see, it's complicated going off grid with your fridge or just about anything. The real world is always different from the figures you come up with but the math will give you an idea what you are up against so you can plan and hopefully hit the balance you want.
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