5000 btu ac on solar

mountainman

What size array and battery bank would it take To be able to run a window unit 6 hours from 12-6 pm  from solar panels and Batteries. 48 volts system.
Only needed when the sun is shining.

mountainman

So nobody wants to touch this?

Photowhit

Some of the equation will have to do with the amount of 'duty cycle' of the compressor, How much it's running, but during the heat of the day we could assume near 100%, And where you are located for hours of sun you will receive and if you need to account for overcast days. If you can angle your array to the southwest and get full sun, as your late afternoon hours would reduce the ability for the batteries to get topped off before sunset. Perhaps that will help you make calculations.

I suspect in Missouri where I am, I could get by with a minimal battery pack of 4 golf cart batteries (about 5kWhs of storage). On days when I need air-conditioning, we are typically sunny. I could do it without a generator backup and only need to sweat once in a while. until late Sept. if it remained hot would be challenging as the sun would be setting earlier. Most of the power needed would come from the sun directly, with a 1000 watt array. If you would use a 48 volt system, 4-100 amp batteries.

Like I said, lots of variables, very tricky question as often it would be difficult  to handle overcast days. I use to live in North Florida, and you couldn't do that there. There is a 'sea breeze' weather pattern that had us clouding up most afternoons with some showers. Also it can be cloudy and hot/muggy there....

BB.

Do you have the window unit already? Can you run it on a Kill-a-Watt type meter from utilty power or a genset for a day or two get get a rough idea of the energy usage?

Using an LG 14,000 BTU Inverter based window unit from Homedepot:

https://www.homedepot.com/p/LG-Electronics-14-000-BTU-115-Volt-Dual-Inverter-Smart-Window-Air-Conditioner-in-White-with-Wi-Fi-Enabled-and-Remote-LW1517IVSM/303947186
https://images.homedepot-static.com/catalog/pdfImages/03/037856e8-8b1a-49d7-a73a-32b23333dc55.pdf

Converting from the Energy Star Tag (they don't make it easy)... $68 per 3 months @ 8 hours per day @ $0.13 per kWH (that is 1/2 to 1/3 my California costs--Ugh).

• $68 per season * 1/$0.13 per kWH * 1/8 hours per day * 1/3 months * 1/30 days per month = 0.726 kWatts = 726 Watt load (sounds reasonable)

http://www.solarelectricityhandbook.com/solar-irradiance.html

Spartanburg SC
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 70° angle from vertical:
(Optimal summer settings)

Jan	Feb	Mar	Apr	May	Jun
3.34	3.80	4.83	5.66	5.85	5.72
Jul	Aug	Sep	Oct	Nov	Dec
5.63	5.27	4.85	4.63	3.66	3.22

If you want to run only (or mostly) under direct sun, assume 50% of array capacity, or:

• 726 Watts * 1/0.77 panel+controller derating * 1/0.50 use of output in less sun * 1/0.85 AC inverter eff = 2,218 Watt array "nominal"

If you base this off of running from the battery bank or panels from March through September, then:

• 726 Watts * 6 hours per day = 4,356 Watt*hours per day
• 4,356 WH per day * 0.52 off grid system eff * 1/4.83 hours of sun per day (March average) = 1,734 Watt "March break even" array

Battery bank is a bit more iffy... Assuming the LG draws no more than 726 Watts (inverter based A/C), and assuming a 24 volt FLA (flooded lead acid battery bank) will support ~500 Watts per 100 AH @ 24 volt running load:

• 726 Watts * 100 AH (per 24 volts) * 1/500 Watts (per 100ah) = 145 AH @ 24 volts minimum FLA battery bank

That way, the Window AC should always start (even if a cloud goes by). But you would not be using more than an 1 or 2 of battery runtime per day on such a small bank--Rely on the Solar panels and full sun most of the time.

If you are running in Afternoons, you might want to think about pointing the array more South West (more energy direct from array in afternoons).

My guess (purely SWAG) would be 4x 6 volt @ 200 AH "golf cart" batteries in series for a 24 volt @ 200 AH battery bank. And somewhere around a 1,734 to 2,218 Watt array minimum.

If you go with a south west array, then the solar numbers look like (note: I tilted the panels a bit more for afternoon harvest in spring/fall--This does "kill" the mid day harvest a fair amount:

Spartanburg
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 55° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.58	3.89	4.72	5.23	5.20	5.01
Jul	Aug	Sep	Oct	Nov	Dec
4.96	4.79	4.64	4.71	3.90	3.52

How you run the window AC will also affect usage... Dave A. here (as I recall) starts the system earlier in the day, on low, to pre-cool the room and then let the system "run on low" through the hot afternoons... Vs just turning on full at 12 noon.

Note that A/C systems do use a lot of energy per day (2x that of an full size energy start refrigerator). So, this is not going to be a "small/cheap" system.

Anyway, a SWAGs (scientific wild ass guess)... Are they of any help?

-Bill

mountainman

Thanks @bb and photowhit. 
Don't no that I would need one that big for a 30 foot camper but thats a great price on a 14000 inverter ac.
Around the same price as a typical ac.
My location is on the east coast closer to Myrtle Beach or Florence SC.
But I imagine the sun hours are closely related.
Yes 12 cents per kw.
 I know it's not practical
To try and run ac off grid when  poco is so cheap.
 I have 4 6 volt Gc Batteries.
And close to 800 watts of solar already.
I have a 40 mppt that I'm not using
I can get 250 panels locally for $60 each.
The biggest cost would be a 24 volt inverter.
And the inverter ac of course.

My house is 1902 two story that's being 
Completely remodeled. The power is off for an unknown amount of time  and has been for 3 months.
So im in a camper till its finished.
And its getting warmer.
 I would rather not deal with my generator.

When I do get power back on.
Solar will be there for  back up as we have frequent outages hurricanes ect.

Seemed odd to me but I  noticed winter production is better at a sw  array setting.
    
So do you think i could I accomplish running a 14000 inverter ac on 1800 watts.
The 800 system I have plus
4 more 250 panels and the 40 amp mppt controller 
 with a cotek sp1000 24 inverter?

burnin_daylight

FWIW, I run 3x 18,000 BTU AC units on solar/battery power. 10Kw array, 48V 75Kwh lithium bank. 

Off grid, and haven’t started the generator in 2 years (except to test it occasionally). Zero down time. AC runs continually, in AZ and HOT. 

I have done several off grids with AC, and I have noticed that most units pull about the same AC amps as their listed BTU’s. So for 5K BTU unit, pulls about 5A @120V, or 600W. For most of my installs I have taken the average running watts, then gone 2X or 2.5X for the solar array, so 1200W-1500W. However, this needs to be adjusted for where you live. (We gets lots of direct sun here). 

Your inverter needs to be able to handle the surge watts, but if you install an Easy Start on the AC unit, it will reduce the inverter size Drastically. 

WaterWheel

For 2 summers I ran a 5000 BTU window AC in N. GA (daytime highs around 85-92 degrees with a poorly insulated house) off of 490 watts in panels with a 318 amp hr 12v battery bank.       I didn't have the best meters at that time but it was usually around 1 pm  before the batteries went into absorb so I wouldn't start the AC until about 2 hours after the batteries went into absorb (around 3 pm).

To keep the batteries above a 50% charge I usually had to shut the AC down about sundown (9pm)

mountainman

@WaterWheel seems I should be able to run it on 780 watts and a 416 ah 12 volt  bank then?
What size inverter did you use?
Did you use a soft start on yours?

WaterWheel

A Xantrex Prowatt 1000 watt PSW inverter.     Back then I didn't know about motor start up surge but the window AC started up with no problems.      I'm still using that inverter on the same solar system to run a small fridge in my shop.     Having learned more over time I'd now go with a 1500 watt inverter.       That 1000 watt inverter won't start my home fridge.

My 316 am/hr battery bank could keep the AC running until midnight but I almost always shut down around 9pm to protect the batteries.