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Array/Bank Sizing for a small Chest Freezer

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  • Array/Bank Sizing for a small Chest Freezer

    I'm wondering how to properly size an off-grid system where the primary use will be to power a small 5.3 cu. ft. chest freezer when I don't really know how much it will run in the summer time at my new location.

    Location Info: Remote woods in southern Missouri about 80 miles due east of Springfield. My land is on a south facing slope at 1400'. Using TMY2 data for Springfield, MO, annual solar radiation should be around 4.9 with December being the lowest month at 2.8 and July the highest at 6.9. March through October, average solar radiation comes out to 5.68 so I figure 4.0 to 4.5 should be a good number to plan on since I doubt the freezer will run much in the winter time.

    Freezer Info: The freezer sips power when the compressor is running. Using a Fluke 334 clamp meter, I am showing 69W when running. The Fluke is supposedly accurate to within 1% but it is several years old so I am sure it is no longer this tight. However, the in-rush current is 1300W when the compressor has been off for 24 hours, so I am going to need a fairly high-quality sine wave inverter to run this. The energy star label, for whatever it is worth, says 215 kWh estimated annual usage but I have no clue what ambient temperature they are basing this on.

    I figure a 24V bank would be best but what size of a bank and PV array would be best to start with if I want to dedicate an array just to this freezer. The freezer will be stored in a small tool shed tucked into the woods next to the clearing for the array. I simply do not know how much it will run in the summer time and I suspect it will not run much at all in the winter time. I will have a generator for backup.

    Any thoughts? Thanks.

  • #2
    Originally posted by N1ESE View Post
    I'm wondering how to properly size an off-grid system where the primary use will be to power a small 5.3 cu. ft. chest freezer when I don't really know how much it will run in the summer time at my new location.

    Location Info: Remote woods in southern Missouri about 80 miles due east of Springfield. My land is on a south facing slope at 1400'. Using TMY2 data for Springfield, MO, annual solar radiation should be around 4.9 with December being the lowest month at 2.8 and July the highest at 6.9. March through October, average solar radiation comes out to 5.68 so I figure 4.0 to 4.5 should be a good number to plan on since I doubt the freezer will run much in the winter time.

    Freezer Info: The freezer sips power when the compressor is running. Using a Fluke 334 clamp meter, I am showing 69W when running. The Fluke is supposedly accurate to within 1% but it is several years old so I am sure it is no longer this tight. However, the in-rush current is 1300W when the compressor has been off for 24 hours, so I am going to need a fairly high-quality sine wave inverter to run this. The energy star label, for whatever it is worth, says 215 kWh estimated annual usage but I have no clue what ambient temperature they are basing this on.

    I figure a 24V bank would be best but what size of a bank and PV array would be best to start with if I want to dedicate an array just to this freezer. The freezer will be stored in a small tool shed tucked into the woods next to the clearing for the array. I simply do not know how much it will run in the summer time and I suspect it will not run much at all in the winter time. I will have a generator for backup.

    Any thoughts? Thanks.
    For anything off grid you design for worse case or else you go dark.
    MSEE, PE

    Comment


    • #3
      You need to get a kill-a-watt meter to measure the consumption for 3 days to 1 week to size the battery bank and the panels.

      Comment


      • #4
        Originally posted by paulcheung View Post
        You need to get a kill-a-watt meter to measure the consumption for 3 days to 1 week to size the battery bank and the panels.
        Unfortunately, I am 1200 miles from the location and it's the middle of winter. Results will vary come August.

        Comment


        • #5
          One good thing is when you don't have much sun in winter but the same time you don't need much power to freeze things. If the freezer running at 69 watts, you can get a 750 watts pure sine wave inverter that have 1500 watts surge for few seconds. If is only the freezer and a few LED light you are run, you can use 12 volts battery bank with 400 amps hours and 600 to 750 watts panels.

          Comment


          • #6
            Originally posted by paulcheung View Post
            One good thing is when you don't have much sun in winter but the same time you don't need much power to freeze things. If the freezer running at 69 watts, you can get a 750 watts pure sine wave inverter that have 1500 watts surge for few seconds. If is only the freezer and a few LED light you are run, you can use 12 volts battery bank with 400 amps hours and 600 to 750 watts panels.
            That is kind of what I was thinking. I picked up two SolarWorld 275W panels last year because I got a really good price on them. They have been in storage since. I may try to get one more and go with a 400AH bank.

            Comment


            • #7
              make sure you get an mppt controller for your panels, with proper setup you should be able to get at least 25 amps from your 2 panels with mppt.

              Comment


              • #8
                Originally posted by jony101 View Post
                make sure you get an mppt controller for your panels, with proper setup you should be able to get at least 25 amps from your 2 panels with mppt.
                I'm thinking of going with a Midnite Solar KID.

                Comment

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