DC Fridge or AC fridge with inverter?

Offgridsteve

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Hi!
I have a small off grid (very) house (16’x20’) and am getting ready to purchase a refrigerator. Originally I was going to use a propane fridge but would rather not have the monthly bill of propane.

As of the other day I was dead set on a DC Unique fridge (6 cubic foot) and still may go that way but...

I’m wondering now if I would be better off (spending about the same amount of $$) buying a much cheaper small AC fridge and putting more money into panels, batteries, inverter etc. My house is wired with AC outlets so going this route could also allow me to start using my outlets for other things such as vacuuming, charging my laptop etc.

I was looking at probably spending around $1,500 for the DC fridge, battery, panel, charge controller etc.

Would I be able to spend about the same amount if I went with an AC fridge and inverter but also be able to have some more power to power other things as well ??

Thanks!
 

sremick

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To do the math, I think we'd need to know the actual price of the AC fridge, the actual price of the DC fridge, and the exact model inverter to determine it's efficiency. There's going to be energy lost converting DC->AC at the inverter, depending on the inverter this could be significant, and a compressor running 24/7 is a big draw. All that said, I'd be inclined to say go with the DC fridge just as a gut feeling since I'm a slave to efficiency, but maybe the numbers don't back that up. You do have a point that with the cost savings you could sink that into more panels and more battery to compensate. But even if you balanced it out, at the end of the day you're dealing with more panels (more area/work required) and more batteries (more space/work required, and replacement costs later in life). So unless the $$$ saved on the cheaper fridge can get you WAY more panels and batteries, and space and maintenance aren't a concern, go DC.

But I'm sure someone else will have experienced advice (I have an AC/DC/propane fridge but I almost always am running it off propane when I'm using it because I don't have enough mobile battery capacity yet).
 

cwstnsko

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I have a small Danby residential (115V) fridge that I installed in my RV when the absortion unit died a few years ago. I think it's a 7.3 cubic foot, so it is close to the size of the DC fridge you mention. I just did a 7 hour test of this fridge running off an older Xantrex XPower 1500 watt inverter. The fridge was cool when I started and the AC was running in the RV set to 75F. Over the course of the 7 hours, my fridge pulled right at 20 Ah from my 12V battery bank as measure by my AiLi shunt battery monitor. This should work out to about 75-85 Ah per day assuming the door would be opened and some warm items added occasionally. Based on what I've been reading DC compressor fridges in that size will still likely draw 40-60 Ah per day. At this point I think I can increase the capacity of the solar enough to offset the difference in consumption for far less than I can by a new fridge, but I already own the AC fridge and the inverter etc., so my math could work out differently than if I were starting from scratch.
 

Supervstech

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Even cheaper, and lower power demand is to get a chest freezer, and adapt it to maintain refrigerator temps.

The thicker insulation walls promote far better energy efficiency.

Of course... you then have to place a chest freezer in the house...
 

tictag

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We're talking about AC fridges and DC fridges as if they are the same thing, they are not. A typical (i.e. cheap) AC fridge will run off a compressor and that technology is cheap because they are mass produced. You can also get AC absorption fridges, which would be just as expensive as DC absorption fridges! But the beauty of absorption fridges is their flexibility ... use gas if you have it, use AC if you have it, use DC if you have it. Great for off-grid use! With a cheap (AC) fridge, lose AC and you're fucked buggered.

I would never buy a compressor-type fridge for off-grid use, wouldn't even bother doing the calculations.

A reasonably sized, efficient absorption fridge will draw around 40W on average in a room temperature environment. That's 960Wh per day, which would require around 240W of PV in Summer, around 960W in Winter, with a 80AH 12V lithium-ion or 160AH 12V lead-acid battery. Easily buy-able within $1,500 budget.

Buy a 10kg gas cylinder as a just-in-case contingency plan, and you're golden. Heating, cooling, sorted.

Edit: Corrected naughty word.
 

Fred S

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To provide a counterpoint - an AC fridge of that size is likely to draw less than 10a (assuming 24v solar) to the inverter. So if you are going to invest in solar and battery storage anyway, and it can accommodate that draw, I can't see spending $1,000 to $1,500 for a small fridge. If you have the solar capacity, the energy is free, regardless of the appliance's efficiency. I've looked before and I'm guessing that fridges that size are $150 to $400, depending on how fancy you want it to be. Also, if you can avoid frost-free, or turn the feature off, that will save you some power.

If you don't actually need a freezer, just a fridge, and you don't mind Supervstech's chest freezer adaptation idea, then that's what I would do. You only need to get an inexpensive external temperature controller, plug it in and you're done. Chest freezers are really cheap and should last for years.
 

tictag

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As I said, I personally wouldn't buy a compressor-type fridge for off-grid use ... though that one does come with wifi connectivity so it is kinda swinging for me!! ;)

No, but seriously, this does kinda look cool (pun intended) and does run off both AC and DC.

And charges your f'in phone too! Right, that's me sold!
 

Primal1

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I installed an old dorm fridge in my 8x16 cabin last week. I have 400 watts of panel and 215ah of golf cart batteries. I flip it off when the sun goes down and back on in the mornings. So far no issues, running an 1100w Krieger msw inverter. I've also been running my 4x36 belt grinder, dremels, heat gun and stereo and added a fan yesterday. So far still making float everyday...
 

tictag

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Sorry, too much coffee... 😵

When I say 'compressor-type' I mean the really cheap 'white goods' type units. Yes, those designed for off-grid use would always be worthwhile considering.
 

ianganderton

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I've seen plenty of people go down the dorm fridge route but then have to replace them after not long enough. The constantly running inverter and relatively high power consumption make then a temporary but cheap option.

The problem with absorption fridges is they struggle to keep low enough temps in hot conditions. They also need venting to the outside.

One of the DC compressor fridges designed specifically for off grid use are my preferred option. If its being used in a vehicle even more so, the movement kills the dorm fridges.
 

Craig

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Go with the AC fridge and the inverter upgrade whatever you need panels are really cheap. Up until this week i swore by using a chest freezer that I turned off at times to keep it from freezing but I got tired of accidentally freezing stuff . So I purchased a large dorm fridge from home depot for $150.00 I used it most of last week in 90 degree weather and I hardly noticed the load. Take any money you save off of a DC or a propane unit and buy more panels. I know chest freezers can switch thermostats but I had a use for one as well so I went with both.
 

HRTKD

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I can run my RV fridge on propane for a loooooooong time. Of all the propane consuming devices in my RV, the fridge is the one I worry about the least.
 

Steve_S

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I have not read all the responses but I will add my Experience on this.
I went down this path as well. when I started building my offgrid place. I already had (still do) a Dometic 12/24 VDC /120VAC + LPG fridge which I was intending on but it turned out to be too small anyways. As I am Full-Time and offgrid it boiled down to what fits my needs, what is cheapest to run (My Inverter is on 7/24/365) and what is most suitable. I wound up buying a Danby Apartment Size fridge which is Energy-Star certified and only uses 250kWh per year. On 24V System, it pulls 5.5A on Start and runs on 3.5A (off the battery bank). It really has only a small impact on my system.

Danby Apartment Fridge "similar" to the one I have: I bought mine for $425 CAD or about $320 USD from Costco on sale.
* Note the stainless ones are more expensive than just the plain white ones.
 

upnorthandpersonal

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If you only need a fridge (not freezer) you can get a A+++ rated one in Europe which will consume around 75kWh per year (with freezer, double that amount). The key is not to use a ridge that is already several years old. The amount of efficiency gains made over the past few years has been tremendous. Also, energy consumption numbers advertised on the energy label are pretty accurate for fridges.
 

RCinFLA

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Definitely stay away from Peltier based DC refrig boxes unless you have a lot of power to waste.

Most of the small, under the desk sized, compressor refrigs you can buy for around $100 are not too efficient either, taking more than half the power of a full sized kitchen refrig.

I have not personally done it but have heard good results on smaller freezer, top lid opening, with modified thermostat to refrig temps. Probably because freezers usually have better wall insulation and top opening lid.

Humidity is the enemy. It takes much more BTU's to condense water vapor out of air then to just cool dry air. A top opening lid really helps reducing outside air rushing into refrig like a vertical door opening does. Then you have to spend more energy to defrost the ice off evaporator coil.

It is sort of comparing apples and oranges but propane refrig is not very efficient in energy consumption terms. It cost $2-$4 worth of propane a day to operate a near full size refrig.
 
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boondox

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Get a decent energy efficient fridge. Expand your power system if you need to. We run two regular fridges and a chest freezer. Between the two households and fridges/frezzer we use 3-4kWh overnight. Not a big deal.
 

Hedges

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You could grab any second hand good fridge to start and put in enough panels to run it. Later, upgrade to a more efficient fridge and you'll free up the power for other uses.

A large modern home fridge will have power usage label in the 500 kWh/year range, 1400 Wh/day. Assuming 5.5 effective hours of sun, 250 W ptc, 300 W stc. That's one panel for about $100. You can probably buy a used fridge for $100 vs. new for $600 to $1000. The math has changed since a decade ago on cost of running a fridge with solar power.

Then there is the cost of batteries. Running the fridge 12 hours on a battery would be 700 Wh, 60 Ah at 12V. That would be one, 100 Ah lead-acid AGM battery at 60% DoD, about $200 and worn out in 3 years. Lithium can cost more, but guys here are getting DIY lithium for the same price and longer cycle life, perhaps 10 years.

If you want enough battery for 3 days without sun, then it would be 6x the price, $1200. That's where a more efficient fridge or a backup generator could be more economical .

You could keep blue ice or salt water ice in the freezer, and have a relay disconnect power to the fridge when the sun goes down. PV panels are cheap and long-lived, batteries are expensive. I put PV power at $0.05/kWh, battery storage at $0.40/kWh

Given the (un-) reliability of new refrigerators (like 5% to 15% of new refrigerators of all brands fail within 5 years) I'm trying to get an old one with electromechanical thermostat for my grid-tie house. I have two that still work great, but one old freezer that doesn't get cold enough any more which I want to replace.

Get a second fridge (maybe chest deep-freeze) as backup in case the main one fails.
 

OnTheRoadAgain

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I was about to buy one of those Alpicool DC refrigerators but then I went to the Alpicool website and actually tried their email addresses and phone numbers...ALL WERE BOGUS and out of service.

Next I looked at mid range DC refrigerators. They started at $500 and went up from there.

I ended up buying a 1.7 cubic foot Galanz AC compressor fridge for $80 (brand new) from Walmart.
According to my Jackery 500, it uses 44watts when the compressor is running and 3 watts when in idle.

f5ff235b-e8a1-43b2-9bdb-8c732f9aaf1e_1.f209c79538c434a484f5847f039dcc06.jpeg


Overnight (10 hours) it uses 300 watt hours. It doesn't even deplete my Jackery 500 overnight.
During the day it runs fine on one, 100watt solar panel.

I'm not sure why so many people are having bad experiences with AC compressor refrigerators ?

For me I wouldn't even consider an Alpicool or ANY DC refrigerator. Solar panels and inverters are so cheap and
the Walmart mini AC refrigerators are so energy efficient it just makes sense.

HOWEVER..if I did decide to go DC...I would buy a DC compressor off of ebay or AliExpress and just change out the compressor
myself before I would invest in a Chinese DC fridge.
 
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