Poor man's super efficient off grid refrigerator

In years past, almost all conventional refrigerators and freezers were terribly inefficient, making them useless to folks living off the grid.  The only feasible off grid options were expensive DC models (such as Sunfrost or Sun Danzer).  While these models are super efficient and work very well, it just wasn't much of an option for those of us on a tight budget.

So we found a great low cost AND super efficient option that you'll love if you're pinching pennies while going off the grid!

vestfrostse215

Conventional AC vs Specialty DC

Thanks to the current interest in energy efficiency and the energy star program, conventional 'fridges and freezers are now an option for off grid users, and at a much more affordable price.

The main drawbacks would be:

  1. The minor energy loss from an AC unit running off the inverter (as opposed to a DC unit running straight off the batteries)
  2. The fact that they still are not as efficient as the specialty DC units.

As mentioned earlier, while specialty DC refrigerators and freezers are wonderful options and are super energy efficient, they are also fabulously expensive (a Sun Frost can cost $2,500 to more than $3,000).

Being on a limited budget, we had to find an off grid refrigeration option that was cheaper but yet super efficient.

Mission impossible?  Maybe not...

Converting a Freezer To a 'Fridge

Since we already had an older efficient AC chest freezer, I decided to convert it into a 'fridge using an external thermostat that turns off the power to the freezer once the temperature probe reaches the temperature set point.  We use this analog external thermostat but there are also good reviews for this digital one too (those are affiliate links which help support our site at no extra cost to you).

Why convert a chest freezer into a 'fridge?   There are a couple reasons why I chose to do this:

  1. Freezers are more heavily insulated than refrigerators (due to colder temperatures inside), so when a freezer is converted, it is more efficient.
  2. Cold air is more dense and naturally falls to the lowest area.  When you open the door of an upright unit, cold air is lost.  When opening a chest model, there is nowhere for the cold air to escape to, and much less is lost.

How Much Power Savings?

Our 7.3 cu. ft. Vestfrost, which unfortunately is no longer made, claims an average annual usage of 197 to 279 kWh per year when being used as a...ummm...freezer :-).  That breaks down to around 530 to 760 watt-hours per day.  When used as a refrigerator, we have found ours to use less than 200 watt-hours per day on an average spring or fall day!  That may sound like Greek to you right now, but I am giving these numbers so you can use them for comparison with other refrigerators.

When searching for a conventional 'fridge, the yellow energy tag on the unit will give an estimate of the annual energy consumption.  You can then divide that by 365 to find out how many kilowatt hours (kWh) it uses per day (roughly).  Multiply that number by 1,000 to arrive at the watt-hour usage per day.  That is a figure you can compare with some of the very efficient and expensive DC models.

For instance, a Sunfrost R-19 uses around 500 watt-hours per day.  Yes, it is larger than our freezer/'fridge, but I have lived with an R-19 and can tell you that it doesn't have a huge amount of extra usable space.  Comparing that with our freezer/fridge conversion, we find that ours actually uses significantly less power!  No, our chest model is not as convenient as an upright model, but when you need efficiency and don't have a large budget, that's a minor inconvenience that is livable.  Bear in mind that each chest freezer is different and you'll have to convert yours and measure it before knowing how much power it uses.

The Impact of Room Temperature

Needing to squeeze even more energy efficiency out of your 'fridge or freezer?  At our previous home, we kept our converted refrigerator in a room that was attached to the house but was unheated.  It gets enough heat from the house to not freeze up but stays much cooler than the rest of the house.  During the winter (when our solar system was not producing as much power) the 'fridge didn't have to work nearly as hard and used much less power.  What an easy hack!

At our current home we do have the refrigerator inside for convenience, but we placed our freezer out in the garage to take advantage of our cold winters and use less power.  Since we don't access the freezer very frequently, it isn't difficult at all.

If using a 'fridge or freezer in a cold environment, be aware that some units may be adversely affected.  For instance, a fridge MUST be kept above freezing (obviously!) so that your food doesn't freeze.  With a 'fridge/freezer combo, be aware that most of the time there is only one compressor for the entire unit, and if the room temperature is cool enough to not trigger the refrigerator thermostat, the compressor will likely not run at all, and your freezer will gradually thaw out (if room temp is still above freezing) or will not be freezing as deeply as you expect (if room temp is below freezing).  And in the case of our chest freezer in the garage, we shopped for a model that specifically stated that it could operate in any cold temperatures.  Some of them state that room temperature must be above 20°F, some of them need to be above 32°F and others even state that room temperature must be above 50°F!  So look the manual over carefully before purchasing.

question1-trans  Using a Kill-A-Watt meter or something similar, how much power does your refrigerator or freezer use?

34 Comments

  • Eugene F (Gene) Augustin

    Reply Reply June 23, 2015

    Excellent article. Thanks.

    I'm on my way out to the garage (where our freezers are kept) to plug in my Kill-A-Watt meter right now.

    Blessings.

    Gene

    • Carole crosby

      Reply Reply May 1, 2017

      Where is the best place to get a kill a watt meter. Are there any special qualities that I should be looking for to do the most testing on both the largest and the smaller stuff. Thanks for any resources. Please spell it out as I am not an electrician.

      • Nick Meissner

        Nick Meissner

        Reply Reply May 1, 2017

        Hi Carole, You can usually pick up a Kill-A-Watt meter at places like Home Depot and Lowes, but I often send folks to Amazon as it's very inexpensive and they have my favorite model (the one that I think is easiest to use. Here it is: http://amzn.to/2pBDXnK

        • sweetgum

          Reply Reply October 16, 2017

          Public libraries often have Kill-A-Watt meters available to check out.

  • John Quade

    Reply Reply June 23, 2015

    We have converted three chest freezers to refrigerators. The first was several years ago for our off grid cabin. Now we have two larger ones that we converted for storing our berries during harvest season. They work great. You can also find the thermostats on ebay, about $50 last I checked.

    • Carole crosby

      Reply Reply May 1, 2017

      Ok, what particular type of thermostat do I need to be looking out for to convert my freezer?I wonder can i still use it with regular electricity? I assume so. By the way is there something I can do to lessen my electricity bill that attaches to the main fuse box, since I am still on the grid?

      • Nick Meissner

        Nick Meissner

        Reply Reply May 1, 2017

        Hi Carole, Here is the one we use (it has an analog dial for temperature adjustment): http://amzn.to/2oPUXmh

        And here is a digital option that many consider to be an upgrade: http://amzn.to/2oTgifg

        Hope that helps!

        • carole crosby

          Reply Reply May 1, 2017

          Thanks for the options and the information.
          I am thinking about wiring a new dwelling with DC current. Where can I study that?

          • Nick Meissner

            Nick Meissner

            May 1, 2017

            Hi Carole, Typically DC is only used for a few select appliances if you want them to be of the super efficient variety (fridge, freezer, ceiling fan, maybe water pump). Conventional AC models may be used for any of those items as well, so you'll just have to weigh the cost vs benefit. I go through all of this in great detail in Module 1 of Off Grid Boot Camp (if you are already a member, go to https://www.offgridbootcamp.com/ogbc-dashboard/module-1/.

            It is possible to do a DC only system, but you will be very limited in what you can run. The vast majority of folks install an inverter so they can run their conventional appliances. As for the wiring itself, typically you will use conventional copper wiring just like what is used for he AC wiring in your home. You'll just need to make sure the wire size is appropriate for the load that is on it. It's a little more than I can cover in the comments of this article, but I also cover sizing wires for a variety of situations in Off Grid Boot Camp.

            Hope that helps. Take care!

          • carole crosby

            May 1, 2017

            Thanks for the DC information.
            I will do more research later and check out the site.

  • Larry Jenks

    Reply Reply June 23, 2015

    Thanks again for a good article Nick. I always enjoy reading your stuff. We have a 12 y/old refrigerator which is an energy star and was pretty efficient when we bought it. It currently draws 1.6 kWh per day which is way more than what you're talking about. When we get a chance we will replace it. I like the chest freezer conversion idea but not sure my wife would like bending over and moving things around every time she wants something out of there....

  • Nick Meissner

    Nick Meissner

    Reply Reply June 23, 2015

    Hi Dave,
    Sorry you had a tough day and were frustrated by this article--just trying to share some helpful info. It isn't a cut and dried "going to cost this much money" because it depends on which chest freezer you go with (or maybe you already have one?). As far as the thermostat, if you click on the link given in the article you will be taken to a retailer selling it with the price displayed there (as we do not sell it). Hope that helps.

  • Dolly M M

    Reply Reply June 23, 2015

    Like always, very interesting article. Jon Quade made it even more helpful by telling us where to find the thermostats, and about how much they cost. Thank you both for this useful information.

  • Lynne B.

    Reply Reply June 23, 2015

    Thank you for being generous enough to share information that has taken your time to learn. We appreciate you & Lisa "breaking ground" and then sharing!

  • Dave Surprenant

    Reply Reply June 24, 2015

    Yes what lynne said You Guys Are Awesome Journey On

  • Dave and heather

    Reply Reply June 28, 2015

    Great article!!! All your articles have been very helpful.
    On a side note.... When are the next sustainable prepparedness shows in Washington ?? Haven't seen any media about it or email from you and Lisa.

  • Kalon

    Reply Reply May 1, 2017

    Thanks for all of the great articles! Very helpful.

  • Carole crosby

    Reply Reply May 1, 2017

    That was great news. Thanks for sending it to me. Not living off the grid at this time.

  • Barry Beach

    Reply Reply May 1, 2017

    Thanks for the great Article very good information even though I'm not off the grid. I'll add this information to my off-grid solar files.

    Barry B.

  • Wanda Krack

    Reply Reply May 1, 2017

    Thanks for the details!

  • Jeff H

    Reply Reply May 1, 2017

    The libraries in our area have kill a watt meters that you can check out for free.

  • Nelson McKinnon

    Reply Reply May 1, 2017

    Lived full time for seven yrs, in a Jayco Designer 36 ft 5th wheel. Had a fridge that runs on 12 v,,110w or propane. It also had a freezer. Might be worth looking into. The rv had a 110 watt solar panel with two 12 v. batteries.

    • Nick Meissner

      Nick Meissner

      Reply Reply May 1, 2017

      Hi Nelson, Thanks so much for sharing that! Yours may not have been set up this way, but for the benefit of everyone else, many of the RV refrigerators that run on propane and electric can use quite a bit of power when in electric mode. I think this is due to an electric heating element that is part of the refrigeration system (strangely enough!).

      Since yours was DC in electric mode, it may have been different, but everyone should be sure to check that out before purchasing something a unit like that and thinking it is an efficient electric fridge :-).

  • ainod

    Reply Reply May 1, 2017

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    Dometic - dependable propane gas refrigerators don't need electricity.
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    • Nick Meissner

      Nick Meissner

      Reply Reply May 2, 2017

      Hi Ainod, Thanks for your detailed comment with all the info about propane refrigerators. It's good for everyone to know what their options are and I should have mentioned a word about propane in the article.

      While propane is certainly an option for a fridge that would use little to no electricity, I have always shied away from recommending propane fridges for a couple reasons...

      1 - Propane refrigerators for home use (at least the ones I'm familiar with) are quite expensive--often similar in pricing to a comparable high end Sun Frost or other DC fridge.

      2 - If I'm producing my own power for free from the sun, why would I want to unnecessarily tether myself to dependence on propane and the regular bills that come along with it. No don't get me wrong...there's a time and a place for propane. If you are looking for an easy way to heat your water off the grid and are not up for a solar water heater or using your wood stove, then propane is a great convenient option that uses virtually no power (while an electric water heater uses massive amounts of power). But when it comes to a fridge, we have so many efficient electric options that cost the same or less than the propane option, so I don't see a lot of sense in going that route.

      There is one exception in my mind to this. If you already live off the grid and are outgrowing your system and don't have the money to enlarge it right now, then switching to a propane fridge or freezer could reduce your power usage enough to possibly make your current system work longer. But even then, why not take all that money you'd put in on a propane fridge and use it to make your power system larger and then you don't have to pay for all that propane.

      Anyhow, I really appreciate you bringing up this option as there may be situations where it is a good choice for some, but this is why I don't typically recommend it.

      Take care!

  • Sue Kirk

    Reply Reply May 2, 2017

    I am really enjoying and appreciating your expertise, Nick. My daughter lives off-grid in B.C., and I pass on what I learn from you. Thank you.

  • tam

    Reply Reply May 2, 2017

    does this work on an upright freezer too?

    • Nick Meissner

      Nick Meissner

      Reply Reply May 2, 2017

      Hi Tam, Yes, the external thermostat should work the same on an upright as it would on a chest style freezer (as long as it doesn't have some advanced features that require it to have power 24/7--not sure what would require that but they are making everything so sophisticated these days). The difference would be that a chest freezer is typically going to be more efficient (all other things being equal). So turning your upright freezer into a fridge should cause it to use significantly less power than it does now as a freezer, but it won't transform an "energy hog" freezer into a super efficient fridge. So for best results you want to start out with a model that is already very efficient in it's class. If your is quite efficient, then you could certainly give ti a try and see how it does. The worst that can happen is you discover that it is not as efficient as you'd like

  • SteveW

    Reply Reply May 3, 2017

    Great info.

    Question, our addition is not heated, in the winter it will get to outside temps, down to possibly 40 below, Celsius. I was told by a refrigeration guy that you can't allow fridges and freezers to freeze at those temps as it will cause equipment damage. Does anyone have actual experience with equipment surviving those temps without issue?

    Thanks

  • Joyce

    Reply Reply May 4, 2017

    It occured to me that this type of fridge conversion would work well even if you ARE NOT off grid. Reason being in a grid down situation or rolling black outs a portable solar unit won't power a conventional refridgerator. But it looks like a portable unit would power a converted freezer to keep your food from spoiling.

  • Harry

    Reply Reply May 7, 2017

    Thanks a lot for the great information your letter and the commenet provide.

  • Doug Smith

    Reply Reply May 27, 2017

    I'm curious, does the inverter run all the time, or does the thermostat start and stop the inverter to supply power to the compressor? What is the efficiency of the inverter, and did you include that power in the demand of the converted refrigerator?

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