Running a dorm size fridge on solar

What are the basics one would need to run a small fridge 24/7? How many panels/batteries/what size inverter? I currently have 4 100 watt panels,four deep cycle batteries and 2000 watt inverter.  This runs pretty much everything,TV, Laptop, Lights, even a portable swamp cooler but not a fridge or the small AC ( i have a generator for the AC. I live in the AZ desert so lots of sunshine here. My system needs to upgrading. Been running it for almost 5 years. Building a new tiny house and would like to have a small fridge again . I have heard that full size units are actually more energy effiecient.

Hi Diana and welcome to Permies.

Fridges use around 200-250W while running, but there's a compressor start-up spike that will be 4-5 times that, but for less than a second.  That would be an issue only if you're trying to run it directly from a power source that's less than 1000W without batteries, but you don't have to worry about that.

Small fridges use less power because they're smaller, but a large fridge (normal size) will use less than twice the energy of a dorm fridge, but have 4-5 times the capacity, so they're about 2-3 times more efficient.  

A normal fridge will use between 1000 and 1500 watts a day, a dorm fridge a little over half that.  If you can get by with a dorm fridge, it'll save you energy, but you can get more capacity with a regular fridge.  If you don't need the fridge space that a normal fridge has, you could get a dorm fridge and a small freezer if you want more freezer capacity.  You could also use a small freezer and a cooler and put a frozen jug of ice in a cooler every day.  Still, a small freezer isn't as efficient as a regular one, probably about in line with the small and large fridges.

You could use your genny to power a fridge or freezer 4 or 5 times a day, maybe less, and that would stop you having to upgrade for now.  Have you switched your bulbs to florescents?  You can, as you've said, upgrade your system with more solar panels and/or batteries depending on where your system is undersized for extra power use.

Hi Diana;   Welcome to Permies!
Sounds like you have a good start on living off grid. You just need to upgrade your system some.
I would start with adding more panels. Here is an item # from ebay for 180 watt panels @ $175 each (272812576939)  I bought 6 of these a year ago.
Next, what battery's are you using ? What size ? L-16 ? or T-105 ? How old are they ?  Flooded battery's or AGM?
Is your inverter pure sine wave ?  Is it a full size unit with a charger built in ? If not you might want to step up.
Have you considered propane for your fridge needs ?
Small quiet inverter generators can be modified to run on propane as well.  I personally use a harbor freight 3500 predator that I run with propane. You can hardly hear it run!

My house is only 128 sq ft. I have one light . It's a desk lamp. I'm just wondering what I'd need for a dedicated set up for the refrigerator.  I'm building a new house.  Slightly bigger. I'd have room for a full size fridge but don't really need the capacity.  My current system serves all my other needs .

I'm using 4 deep cycle marine batteries 12v. I don't know about the T or the L . I will look when I get home.  I'm pretty sure the inverter is a sine wave.  I'm not fully  understanding the charger part.  I use 20lb propane tanks . I'd be concerned about how often I'd have to refill them. Not to mention propane refrigerators are expensive.  

What do you mean by full size unit with a charger built in? I'll take a picture of my set up when I get home.  I really appreciate the input.  😁

That would help a lot, Diana.

Hi Diana;
Yes, Please , some photo's.
Sounds like your using 4 , 12 volt  marine battery's.  They work, but are not as desirable. Are they older or new ?
Most off grid systems use 6 volt or 2 volt deep cycle battery's.  
A T-105 trojan battery is 6 volt, it is a comparable size / shape as your current battery's. They would work much better than your 12 volter's.   L-16 deep cycle battery's are an off grid standard.  Much larger than your current battery or the t-105's.  They will take the abuse ( like an A/C unit ) that a smaller battery can not. They can also absorb more power from extra solar panels.

Inverters)  Some are very compact and are basic units. They don't cost much and they generally do not last as long.
The larger full size, pure sine wave inverters have a battery charger built in. Are wired to have a generator connected to it.  When you start your generator , all in house power is switched from the battery's  to run directly from the genset, the battery charger inside the inverter is also running at the same time and recharging your battery's!  

Yes, the new propane  fridges are expensive. I know I own one. But it was a great investment, (they last almost forever with no moving parts)

12 volt sunfrost freezers and fridges are available but also very spendy. I have plans to buy their chest freezer later this summer.

We run a full size fridge with 6 L16 batteries and 2000w of incoming power. We are at full charge most of the day on sunny days. We have a backup generator that gets used during monsoon and winter. The biggest draw as Timothy states is the compressor start up, it's a heavy 800w (still less than your average microwave) but quickly drops to the 200w draw. We changed to the electric fridge after calculating the cost of ruined food in our propane fridge, we found the temperature did not maintain well with teenagers. (too much time staring at an open fridge).  You sound pretty energy frugal, so I think you could get by with less system than we have.

Here are some photos. Everything is going on 5 years old. When I first set this system up it ran a small dorm sized refrigerator and even my swamp cooler but eventually I started losing power over night and then it wouldn't sustain the fridge anymore even during the day. I am guessing I overloaded it and damaged the inverter maybe? I am going to look into upgrading the batteries. I think i may need to replace the inverter as well. How long will a propane refrigerator run on a 20lb tank? The part i like about the solar is not having to refill somerthing.

PS.yes, those are my adorable children in the photo and no they don't live with me

I am getting the feeling I definitely need to invest in better batteries!

These seem similar but have drastically different prices. I'm not necessarily looking for the cheapest but often more expensive doesn't always mean better.

The L16 is a true deep cycle, made for the long discharge of solar use. We found they last longer for us. Ours are 5 years old and going strong. With batteries, lifespan all depends on the depth of discharge and the frequency of discharge, plus the construction of the lead plates. a good comparison is available here:
https://www.solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html

I've been testing a used chest freezer that's managed by a temperature controller like this one on Amazon. I plug it all into a kill-a-watt meter, and in the warm garage the freezer was using about 890 watt hours per day at 0F. With the controller turned on to keep the temp at 35F +/- 2F, the power use dropped to 240 watt hours per day. So if this is just for fridge use and not freezer, a used chest fridge and a $20-40 controller could be a good combo.

Forgot to say, the propane fridge we had was a 9.7 cu foot $1000 unit from the big box store. It ran for 2 and 1/2 weeks in the high heat of summer on 20lb tank of propane. It went farther during the cooler times, but I disliked the unpredictability of running out. Spent plenty of time shaking a tank trying to divine how long it had left.

Plugged in my Killowat thing.  I'm currently running the swamp cooler , TV, dvd player and charging my tablet. Once the sun starts to go down I'll see a significant drop.

you   might consider a 5 cu ft frezer w/ a tem8p controll switch on it oe panel 100 w no problem i 1ooah solar chrome bat total cost for freezer/switch/panel and battery 400 3 years now no problem //we are just outside douglas and all works well//sure wife[aggie] would help you  any way possible///she designed our passive solar tiny house and we use no heat or cooling

Diana;
Here is a link to my local off grid store   https://www.backwoodssolar.com/   They have lots of good info for you to read up on.
I believe the deka battery in your photo was a misprint.  The L-16 is the battery to go to.

My propane fridge is a 17 ft with large freezer. Diamond brand made by the Amish. Cost with shiping to northern Montana was, $2400 …  It is hooked to our 250 gal tank so I cant say exactly how much it uses, other than bunches less than the smaller old servel units.

You might look at the Sunfrost 12 volt units , you do have plenty of sun.

Having lived with a solar electric system for over 35 years, I can share a Thumbs Up for Sunfrost. Our first off grid refrigerator was an old (1940s) Servel propane one. It worked fine for its 'age', but in the (10?) years a that we lived with it we put enough propane $$s into running it to have paid for the Sunfrost! An advantage of the Sunfrost is that its IS very efficent and if you get a DC model it can run on your batteries if your inverter dies. The disadvantage is its not 'frost free' and not as 'large' (inside space) as most households seem to want.

Our RF16 (refrigerator-freezer/16 cf) ran on 2 60 watt (12VDC) panels. www.sunfrost,com

Batteries are the heart of a solar system. After using Trojans at first, we upgraded to Rolls - https://www.rollsbattery.com/

Diana Greer wrote:Plugged in my Killowat thing.  I'm currently running the swamp cooler , TV, dvd player and charging my tablet. Once the sun starts to go down I'll see a significant drop.

We have had this a while, but it still is a great tool to really know exactly how much energy an appliance actually uses -

http://www.energytools.com/pwrmeter.htm

Couldn't be more simple to use, plug the meter into an outlet and then the appliance into the meter. We have even taken this into a store to measure an appliance before we purchase. AC only though.

thomas rubino wrote:

12 volt sunfrost freezers and fridges are available but also very spendy. I have plans to buy their chest freezer later this summer.

Thomas this will sound odd, but we actually (now) have 2 chest freezers - one little 5 cubic foot (probably made in China) that worked well enough for us that we added a 9 cubic foot Frigidaire so we could increase our storage capacity. (buy in bulk and shop bi-weekly/on sales) We recently turned our Sunfrost RF16 freezer into additional refrigerator (simple dial settings) space and use the chest freezers.

Our overall system used to be 1.3KW and ran our efficient modern house nicely. But we have also figured out a few tricks such as making our dishwasher go from 900 watts to 90 watts with nice clean dishes too.

A fresh set of golf car batteries would be a fine improvement. More capacity amd longevity than what you have in place. They are tired by the sounds of it. You can get duracell 220ah 6v batteries nationwide for about $115 each.

Our Danby under-counter refrigerator consumes 750 watt hours a day to operate. I placed 1" reflective foam on the back where it felt cold to the touch.

A 750W array dedicated to it would be good for winter operation at Michigan.

We do not use it in the deep winter (November to march) 440ah at 24v is not enough storage for long strings of cloudy weather, no generator.