Solar + Batteries = refrigerator use????

[Boeing]

Guys, I have 5 deep cycle batteries, all with "750amps Cold Cranking Power" which I don't know how to interpret.
Feeding these are 5 100W solar panels. I want to add a small refrigerator powered by an inverter to 120V. Advertised to draw roughly 1 amp.
That sounds OK, I think. I worry about nights and 3 or 4 cloudy/rainy days when the solar panels are inop.

Do we have any engineers here who can tell me if this is a doable idea or am I going to kill my batteries?
BTW, I intend to replace 2 of my 100W panels with 200W panels next week.
Thanks

 

[ericm979]

1amp @ 12v? That's so small that it will go a long time on fully charged batteries.

 

[Renze]

BTW, I intend to replace 2 of my 100W panels with 200W panels next week.
Thanks

Those 200w panels will have their own controllers ? Putting different capacity, or even just different age panels on the same inverter/controller, will draw them all to the capacity of the lowest panel, i am told.

 

[Minsid]

500W @ 40% duty cycle = 0.2kwh (Assume day/night and a little cloud. You can probably get the real annual PV duty cycle for your location.)
1A @ 120V = 0.12kwh (not sure on the duty cycle of the fridge, assumed 100% and this seems low, small fridge?)
Estimate 40 amp hours in each 12V battery = 0.48 kwh each battery, 2.5kwh total (this is a low estimate)

On average the numbers work with some margin for efficiency losses but winter gets iffy without the bigger panels. The batteries will only run the fridge for ~20 hours. That is enough to get you through a night but not a cloudy/stormy/snowy day.

As I recall you'd want at least 3 days of battery capacity assuming no charge input.

Really need to know the duty cycle of the load. How much power does it pull over a day?

 

[Boeing]

1amp @ 12v? That's so small that it will go a long time on fully charged batteries.

No, I'm sorry. The fridge would run thru inverter to operate at 110-120V

 

[Boeing]

Those 200w panels will have their own controllers ? Putting different capacity, or even just different age panels on the same inverter/controller, will draw them all to the capacity of the lowest panel, i am told.

Hmmm, I plan on just piggy backing them into the existing controller. I would have 3 100W panels and 2 new 200W panels.

 

[Boeing]

500W @ 40% duty cycle = 0.2kwh (Assume day/night and a little cloud. You can probably get the real annual PV duty cycle for your location.)
1A @ 120V = 0.12kwh (not sure on the duty cycle of the fridge, assumed 100% and this seems low, small fridge?)
Estimate 40 amp hours in each 12V battery = 0.48 kwh each battery, 2.5kwh total (this is a low estimate)

On average the numbers work with some margin for efficiency losses but winter gets iffy without the bigger panels. The batteries will only run the fridge for ~20 hours. That is enough to get you through a night but not a cloudy/stormy/snowy day.

As I recall you'd want at least 3 days of battery capacity assuming no charge input.

Really need to know the duty cycle of the load. How much power does it pull over a day?

Wow, great info and thank you.
I plan on replacing 2 of the 100W panels with 200W panels so I would have 700W during sun.
The fridge is a 3.1 cu ft. mini and advertises .87A draw. As you mentioned it's iffy considering that I use LED lights and a 12V water pump for a 15 minute shower every night. Due to frozen pipes I winterize and leave every Dec 10th or so and would unplug the fridge.

 

[2manyrocks]

You might research RV refrigerators like these: CheapRVliving's Amazon Page - Fridges 12V and check the Cheap RV living posts on YouTube.

 

[FPGT72]

You really need to head over to diysolar.com. The folks over there can really help you out with this.

To be honest you will not know till you try. There is a loss when going through the AC to DC inverter. You will need to factor in that loss.

I would also invest in this thing called a Killawatt

This will tell you just what your appliance is actually pulling in the real world. They are pretty inexpensive.

Mixing 100 and 200W panels does not work quite like you are thinking it will. With solar panels lots of things to learn in the series vs parallel and just what each way does.

You are also going to need a charge controller, this is different from the inverter. It will stop the solar from charging the batteries too high. You will also need some form of low voltage cutoff. Both of these things are very hard on the batteries.

good luck

 

[Williy]

They do not recommed mixing solar panels on the
same MPPT controler also the solar panels are usually
in groups of 3 same wattage. I would get one more 200
watt panel and sell the 100 watt panels. Then you would
have 3 x 200w = 600 watts. I have 12 250 watt panels 4
groups of 3.

willy