Off grid solar refrigeration

Hey all! I just signed up today and am excited to have joined a forum with like minded folks.

I'm into self sufficiency and my goal is to go completely off grid sometime in the future, one thing at a time. We have been using solar powered lighting in the house for over a year now and we love it.

During a wind storm about a month ago the power flickered several times and fried the compressor in the chest freezer we had been using for a year as a fridge, so getting refrigeration is first. Side note: the chest "fridge" saved us a lot of money on our electricity bill each month.

After that is wood heat, but our setup isn't ideal. Insurance company won't insure us unless a licensed pro installs the rocket mass heater. We know of nobody in this area that does that and we absolutely cannot afford to bring ernie and erica over here to do it. So, it will most likely be a wood stove. My desire is to use the wood stove to cook and bake as well as heat our home and heat water. Already use my solar oven to cook and heat water but it isn't gonna heat our home and it only works on sunny days lol!

I would like to buy a sundanzer chest fridge and run it on solar, with the option to run it on ac if we need to. Looking at their dcr154 5cf chest fridge. Gonna call and ask if they can install an ac thing. I have some solar components already but am in need of solar savvy folks to guide me.

Nice to meet you all!

M James wrote:Hey all! I just signed up today and am excited to have joined a forum with like minded folks.

I'm into self sufficiency and my goal is to go completely off grid sometime in the future, one thing at a time. We have been using solar powered lighting in the house for over a year now and we love it.

During a wind storm about a month ago the power flickered several times and fried the compressor in the chest freezer we had been using for a year as a fridge, so getting refrigeration is first. Side note: the chest "fridge" saved us a lot of money on our electricity bill each month.

After that is wood heat, but our setup isn't ideal. Insurance company won't insure us unless a licensed pro installs the rocket mass heater. We know of nobody in this area that does that and we absolutely cannot afford to bring ernie and erica over here to do it. So, it will most likely be a wood stove. My desire is to use the wood stove to cook and bake as well as heat our home and heat water. Already use my solar oven to cook and heat water but it isn't gonna heat our home and it only works on sunny days lol!

I would like to buy a sundanzer chest fridge and run it on solar, with the option to run it on ac if we need to. Looking at their dcr154 5cf chest fridge. Gonna call and ask if they can install an ac thing. I have some solar components already but am in need of solar savvy folks to guide me.

Nice to meet you all!

Welcome to permies...
You are going to get two opinions on the 12 volt freezers. They are a good unit but do not use less energy then their off the shelf big box store freezers of the same size that are energy star rated. So if you are considering the ac model anyways I would say that you buy a standard one and spend the extra money on a starter off grid system. The extra 1000 dollars for the sundanzer will get you 2 deep cycles, solar panels, controller and a small inverter to run it...  just a thought. I know people who have them love them though.
A good surge protector power bar is a very good investment as well...
Cheers,  David

You see to have some good plans in the works.   To play devil’s advocate,  check on the costs of buying a smaller, new, 110v fridge, inverter, and the extra panels and batteries to keep it running. Compare total costs with the dc unit.  

David, the appliance repairman said a surge protector wouldn't do any good, which didn't sound right. We've never lost anything before due to flickering of electricity. Maybe just bad luck?

Another person on permies said his very large freezer just sips power, so your post confuses me (which ain't hard to do...see below lol).

I was under the impression that a dc chest fridge run on solar wouldn't use as much power as an ac one run on solar. One reason i thought that is because the dc (power) wouldn't have to be converted to ac to be used on solar, but ac would. Hope you get my drift. I'm not considering an ac freezer. The only reason ac came into my post was that if something happened and i needed to plug it into the grid, i could. Like if the sun didn't shine for a week or something.

Here are the components i already have, which i bought a few years ago for a different project:

Renogy rover mppt 20a pwm solar charge controller 12/24v. Max solar power = 12v 260w. Or 24v 520w.   Max load power = 12v 240w. Or 24v 480w

Mighty max solar 500w pure sine wave inverter. Dc to ac (in case i do decide to get the ac chest freezer)

The sundanzer chest fridge, in 90 degree air temperature, uses 240 wh/day. If my calculations are correct, this would make it 20 amps, but that sounds like an awful lot of amps. That can't be right. Probably has something to do with it being watt hours instead of just watts?  Ok then, is it 240 ÷ 24 hours in a day? If so, is it .83 amps?

Somebody please help me or else put me out of my misery LOL!

John, a new 5cf chest freezer is around $200. I was using a johnsons control temperature thing on it to make it into a fridge. Those are around $65.

The sundanzer 5cf chest fridge is $800, and that doesn't include an ac option. Wonder if there any adapters available to make it usable on ac? I'll look into that.

In my previous post you will see that im lost as far as figuring out anything electrical. I have no idea whatsoever which of the setups will take the least amount of juice to run. I have misplaced my killawatt gadget so even if i had a new chest freezer i wouldn't be able to figure out its energy use grrrr

We were very happy with the performance of the ac chest fridge until the compressor went out of it. Doggone the luck!

I'm not sure how that exact fridge works, but here is my experience with two different types of electric cooling things off the grid:

1. Standard chest freezer designed for on grid use - it has a surge of around 500 watts when switched on, and then uses 100 watts an hour continuously. I'm not sure if it always uses this because we switch it on for only a few hours a day when it's sunny, and if it would only be using power sometimes if it were on 24 hours a day, but that is how it works for us.

2. Engel 38L chest fridge (designed for off-grid/4wd/camping use) - there is no surge, the compressor switches on for a few minutes at a time every so often. On the hottest days it's on for maybe 15 minutes in an hour at most, using 40 watts when it's on, so less than 10 watts per hour.

When I looked into getting an off grid fridge, it appeared that some of them used the same amount of electricity to an on grid fridge, and others use hardly anything at all. It was hard to get exact information about them, maybe because they behave like the chest fridge that I have, using a certain amount of amp hours when the compressor is on, but it's hard to say exactly how long the compressor will be on for each day.

M James wrote:David, the appliance repairman said a surge protector wouldn't do any good, which didn't sound right. We've never lost anything before due to flickering of electricity. Maybe just bad luck?

Another person on permies said his very large freezer just sips power, so your post confuses me (which ain't hard to do...see below lol).

I was under the impression that a dc chest fridge run on solar wouldn't use as much power as an ac one run on solar. One reason i thought that is because the dc (power) wouldn't have to be converted to ac to be used on solar, but ac would. Hope you get my drift. I'm not considering an ac freezer. The only reason ac came into my post was that if something happened and i needed to plug it into the grid, i could. Like if the sun didn't shine for a week or something.

Here are the components i already have, which i bought a few years ago for a different project:

Renogy rover mppt 20a pwm solar charge controller 12/24v. Max solar power = 12v 260w. Or 24v 520w.   Max load power = 12v 240w. Or 24v 480w

Mighty max solar 500w pure sine wave inverter. Dc to ac (in case i do decide to get the ac chest freezer)

The sundanzer chest fridge, in 90 degree air temperature, uses 240 wh/day. If my calculations are correct, this would make it 20 amps, but that sounds like an awful lot of amps. That can't be right. Probably has something to do with it being watt hours instead of just watts?  Ok then, is it 240 ÷ 24 hours in a day? If so, is it .83 amps?

Somebody please help me or else put me out of my misery LOL!

To clarify the total amount of power used by a modern ac chest freezer that is energy star rated converted to a fridge will be extremely close to its dc equivalent at a much lower price. The dc chest fridge's advantage is they can run directly off of a 12 volt battery so you do not lose any power converting from dc to ac. If you look at the dc appliances specifications in freezer mode and compare it to a standard one you will see for yourself. You wont find specs for a standard chest freezer in fridge mode so you need to compare freezer to freezer.
.83 amps is your hourly amps. Your fridge wont be running all the time. Running amps is probably in the 8 amp range when it's on. So 12 voltsx8 amps for 96 watts When its running probably in the 10 to 15 percent duty cycle range or 9.6 ish watts per hour...
Cheers,  David

First a quick explanation of how the freezer may have failed.  A surge suppressor will protect part of the fridge/freezer from problems.  The controls and the electronics it can protect.  But it does not protect the compressor.

The compressor is running and under normal circumstances it runs for longer time period and then is off for a longer time period too.  During the long off period the pressure in the compressor bleeds off so the compressor is starting against a fairly light load comparatively.  If the power blinks the compressor stops but then the power comes back on before the compressor has a chance to bleed its pressure down.  The motor isn't strong enough to start against this high load.  Now the compressor tries to start for about 30 to 45 seconds.  During this time the winding in the compressor is getting warmer.  Eventually the thermal overload outside the compressor trips and kills the power.  Normally the thermal overload takes enough time for the pressure to bleed down that by the time it cools down enough to reset the compressor is ready to start.  No one ever knows the compressor was locked solid for a bit because everything resets in 5 or 10 minutes.

Now this can lead to multiple failure modes.   1.  If the power bounces repeated for a time slightly less the thermal overload trip each cycle gets the winding inside the compressor hotter while the thermal overload being outside cools faster.  The compressor may even manage to start while the cycles are happening but the power goes out again and it stops.  If those cycles continue at the right pace the winding gets hotter till it burns up.  2.  The thermal overload fuses in the on condition for some reason so now the compressor becomes a resistance heater because the compressor can't start.  There again the cycling makes this more likely to happen.  3 in cheaper design compressor systems the relay that runs the compressor and the thermal overload are part of the same mechanical system.  The contacts in the main relay fuse and the thermal load can't open them so there again the winding burns up.  It is bad luck or protection system failures that take out the compressor.  And no surge suppressor will will protect against this.  An inverter and battery would because then the power should never blink repeatedly to the compressor.

Now a quick comment on power calculations.  A typical household to light commercial compressor unit will be rated between 1/6 and 3/4 of a horsepower.  But remember other things can be running at the same time.  In a large side by side 4 fan motors, ice maker motor and door lights.  Older machines the door light bulbs draw 40 watts each.  Also the controls draw a bit of power.  The other major power draw is the defrosters but they typically only run while the compressor is off so ignore them typically in the math.  So if the compressor is say 1/2 hp and the rest adds another 1/4 hp worth of electric draw that is what you are working with.  3/4 hp = 560 watts  But this still isn't enough to size the inverter.  The problem is that the surge electric draw is far larger on starting.   So your inverter needs to cover both run and surge needs.

Now there is another option  I have a newer chest freezer with dead compressor so I have been looking  at options.  If I put a 12/24 DC volt compressor in it  then I can avoid the expense of a full DC unit while getting its benefits.  Figuring it is going to take a bit over $350 for the compressor, electronic controller, gas and other materials.(doable if I can do my own work so there is no other expense(I have most of the tools and skills needed)  It is marginal as my freezer is too large to match the compressor's volume rating.  But it is high end with great insulation so can I push it a bit more?  What about building an insulated case around the freezer and moving condenser to outside it?  By doing DC as the primary I would be all set for solar power but a large switching supply and the system would run on AC too.  Here is the link to the compressor.  The electronic controller costs about as much as the compressor.

DC compressor

If I did it there are 3 other dream systems I would like to try to set up to include at a future date.  1.  Completely passive solar thermal powered  refrigeration system so the DC/mechanical system only rarely ran rarely.  2 Wind powered compressor dumping heat else where and then blowing small quantities of really high pressure air into the freezer allowing for air powered cooling.  3.  a suction line run diagonally thru the insulation to allow freeze drying without a fancy freeze drier.  A simply paint pot or pressure cooker in the freezer and cold for the cold chamber with a hose connecting to the inside wall.  Outside the freezer another pot and the vacuum pump.

I went the completely AC route and I couldn't be happier.  I think DC appliances are very overpriced, and the money is better spent getting more solar panels and bigger batteries.  That's how I did it and now my off-grid cabin is fully energy independent, with solar powering everything, including my 240VAC well pump, refrigerator, and air-conditioner.  I built a 48V system with 4500W of panels, Trojan L-16 batteries, and a Schneider XW+6848 inverter.  It does everything.

The folks over at Living Energy Farm sell the Sundanzer as well as other solar gear, and might be able to offer some insight and advice.  

They've used their Sundanzer fridge for 3 years now direct from solar with no batteries.  Here's a wiki for Living Energy Lights with some basic product info, as well as video descriptions, and various farm innovations, and of course, a link to their websites.

since refrigerators come in different sizes and types, they also call for different amounts of solar power to operate. To uncover the amount of solar power to run a refrigerator, you need to consider the length of time you plan to run your fridge. Determine the number of solar panels required in operating a freezer and a fridge by dividing your fridge’s number of watts by the number of watts your solar panel generates. Thus, if your charge controller, solar panels, fridge, batteries, and freezer are efficient, then they can significantly minimize your solar power requirements.

For my old RV fridge I replaced the guts of my fridge with a 12 volt fridge kit made by JC Refrigeration. Look forward to trying it out.