Minimum battery or other options to run standalone AC during solar hours

[zerman]

I salvage properties and I lucked into some solar parts including ten 280w panels, a couple 3kw 48v inverters and epever MPPT charge controllers. However no batteries. I'm in AZ and looking to setup a system to "off grid" a standalone AC unit I can use to reduce my cooling costs which are 90% of my electricity bill anyway. What's the minimum setup in terms of battery I could use that would just run the AC units (either window or potentially a mini split) while the sun is out? Or is their a conceivable way to do this without batteries at all?

I don't care about using the system to power anything once sun is off peak. Given that all the parts of the setup are already 48V I wasn't seeing a lot of battery options on the cheap. I expect to use this only though the rest of the hot months before reconfiguring it in a more permanent setup with more panels and different charging hardware and some real battery storage so I'd like to put in as little as possible now.

Thanks so much and I'm really happy Will setup this forum.

 

[snoobler]

Need to source the unit and determine power needs. The most efficient is the mini split. A 12000 btu mini split uses about 500W. Watch that you don't get a 240V unit. They are the most efficient, but sticking with 120V should be fine. Just won't get as high a SEER.

You could do it without batteries at all, but that's not in my skill set. IMHO, easier to just buy walmart batteries.

Get $360 worth of the Walmart 29DC Everstarts. It's hard to find ANY battery that cheap. That will give you your 48V. Those batteries could run a 500W unit for about 6-8 hours (even though you don't want to, it helps you save during all these cloudy AZ days we have). Since the panels are free, you don't need to just run on peak. Figure out what the limit of the solar controller is and size your array accordingly. Having a lot more panels than you need widens the window of sufficient solar. If you mean literally, the APS/SRP peak hours, then you can adjust your panel tilt to favor capture during the afternoon hours.

Alternatively, if you can find 4X similarly sized used 12V that all hold a charge, that would work too, but without knowing they're healthy, you'd want to make sure they don't run the AC for very long if ever.

With 2800W of panels (about the same as my deployed array), you could conceivably run your A/C from about 8am to 5am assuming it runs full blast all day and never touch the batteries. You could shift that time window based on how you tilt your panels - favor the Southwest to shift it later in the day. You could also use a small portion of your batteries to extend into the later hours until the array completely quits putting out power.

 

[zerman]

Thanks for the advice. I have a ~500 watt window unit from a similar reclaim so I think I start with that and I come across those pretty regularly so I don't care if it burns out. My plan was to set it to high and run it on a timer as long as it will run from the power then time it off for the day. Given the panels were free I don't care about efficiency very much. I occasionally find mini splits so I will keep an eye out for a 110v unit. Controller is an Tracer6415AN which looks to be 60 amp 48v.

Given that I have the extra juice, consider this a temporary setup and don't care anything than the AC would building out a micro 48v lifepo4 module that acts as a 5-10 minute buffer be a dumb idea? Could set it up to gradual shutdown the AC, wait till it's full to start it back up, full sun days would just run.

What's special about the 29DC vs any other lead acid setup?

 

[snoobler]

If you got it, use it. 500W is a manageable load. The controller can handle the full 10 panels if need be.

5-10 minutes of battery is a narrow window, and as seasons change and solar hours shrink, you'll likely miss your window multiple times. Such low capacity has other limitations with solar charging. The timer is a good idea, but there are definitely clouds during monsoons, so 5-10 minutes might not be enough. Not sure what you mean about gradual shutdown. The A/C is usually a binary on/off situation. It can't be run at lower setting, but it's still on/off cycled as necessary. You may be describing something superior that I'm not seeing though.

FWIW, I use wifi smart plugs to cycle a 325W fridge on and off to have it run only during solar hours. Can control it manually in person or control it 150 miles away with an app and set events such as on @ 7:00am and off at 4:30pm daily.

Nothing at all special about the 29DC. They're "deep cycle", and they have a lot of capacity for the price. IRRC, they're $80-90 each, and they're about 80Ah of usable capacity.

 

[snoobler]

Also, to put it into perspective, assuming you're paying a premium at around $.20/kWh (peak vs. off peak).

If you actually replace 500W for 12hr/day with solar, that's 6kWh. You're saving $1.20/day

 

[Sunny Days]

I ran a 12 btu, 240 volt minisplit with 1500 watts in solar panels and 4 golf cart batteries that cost about $500.
This ran all day from 9am to 5pm without touching the batteries! All solar.
Batteries only came in during clouds or if it rained.

 

[zerman]

Where did you get the golf cart batteries at that price?
It's not a watt for watt replacement. House AC has to cool a lot more area than just a window unit and does not have zones. Can also cool to potentially lower setting while I am not there because it's almost "free". Its supplementing cooling and in a more targeted way. Total savings is probably limited to $750-1200 for the remainder of the year which is why I'm cost sensitive on it for now.

 

[snoobler]

Costco carries 6V golf cart batteries for about $125, but "golf cart" batteries means different things to different people. A new set of 12V Trojan T-1275 are about $1000, and those are overkill for your needs.

IMHO, $/Ah on those Everstarts is hard to beat.

 

[Sunny Days]

Sams, they were 90 something and they charge $15 extra for recycling or something.
Was about $120 for each battery.

6 volt 220 amp hour.

 

[snoobler]

Yep. a 48V system would need 8. Gettin' spendy.

 

[mjbeam]

I have that same charge controller running a 5000 btu window AC with 700 watts of panels. I have three 100AH AGM batteries in parallel. If you only want to run the AC when the the sun allows you shouldn't need to invest much in batteries. Right now my solar is fully powering my AC with enough power remaining to run a laptop, lights a few fans and dumping an amp or so into the battery bank. From about 10 am to 2 pm or so, all power is provided by the panels, except when the AC starts up. For a second or 2 the inverter draws up to around 1000 watts from the batteries until the MPPT catches up and starts providing the current. So if you over panel the controller a bit, and only run the AC when the panels can provide enough power for the AC, you only need enough battery power to run the AC for the short time between when the AC compressor kicks in and the MPPT ramps up. With over paneling you should have a pretty wide window where you can get enough solar to run the AC.

 

[zerman]

Great feedback, thanks

 

[tictag]

If you don't actually need the batteries and you're only looking to power the A/C during the day, you might want to consider buying a super-capacitor module instead to manage the A/C surge. No batteries required.

If you do end up buying these cheap lead-acids, I would recommend against discharging them daily much below 50% - they'd only last 6 months or so. You could use a cheap VSR (Voltage Sensing Relay) to automatically disconnect your inverter or, if the inverter has a low voltage disconnect, set it about 50% SoC for your battery e.g. circa 12.2V per 6 cells or 48.8V.

 

[TheeBigGuy]

I ran a 12 btu, 240 volt minisplit with 1500 watts in solar panels and 4 golf cart batteries that cost about $500.
This ran all day from 9am to 5pm without touching the batteries! All solar.
Batteries only came in during clouds or if it rained.

I want to match what you have done with the minisplit...What controller are you using?... What wattage was the minisplit using..I want to use this for heating as well..Have you done that?...thanks for any help...

 

[Sunny Days]

Its a 23 SEER Innovair unit, dont know the wattage.
At The time i was using an EPEVER 40 amp Charge controller
Amazon link It cooled a 14" x 14" room. Im in Puerto Rico so i have sun all day so your sun hours will
vary! This charge controller lasted me 3 years, it just died a few weeks ago!
i ran this settup for about a whole YEAR! Then added a Hybrid MPP all in one and that could deliver another 60 amps of charging with 8 panels.

When the Aircon would first start it pulled about 1000 watts then would drop way below, All inverter minisplits are like this.
Heating wont work with my specs, heating uses way to much power,

 

[TheeBigGuy]

Its a 23 SEER Innovair unit, dont know the wattage.
At The time i was using an EPEVER 40 amp Charge controller
Amazon link It cooled a 14" x 14" room. Im in Puerto Rico so i have sun all day so your sun hours will
vary! This charge controller lasted me 3 years, it just died a few weeks ago!
i ran this settup for about a whole YEAR! Then added a Hybrid MPP all in one and that could deliver another 60 amps of charging with 8 panels.

When the Aircon would first start it pulled about 1000 watts then would drop way below, All inverter minisplits are like this.
Heating wont work with my specs, heating uses way to much power,

Thanks for the information..What size is your battery bank for this?

 

[Sunny Days]

At first i was just 220 amp hours at 24 Volts, lead acid
(4 golf cart batts in series) this could run all day, batts compensated for clouds. At about 5:30pm it would start using battery since i wouldnt have enough sun. so i would turn it off...

Then i added 8 more batteries, now its 24V and 660 Amp hours, about 16kw
draining to %50 would leave 8kw. I Run this aircon all night and i consume about 4 kw during the night.
Less if in ECO mode.
I got now 2 LifePo4 banks, one is 24v 200AH the other is 24V 280Ah, Neither one is connected at the
time since i just got the BMSs and havent wired anything.

 

[TheeBigGuy]

At first i was just 220 amp hours at 24 Volts, lead acid
(4 golf cart batts in series) this could run all day, batts compensated for clouds. At about 5:30pm it would start using battery since i wouldnt have enough sun. so i would turn it off...

Then i added 8 more batteries, now its 24V and 660 Amp hours, about 16kw
draining to %50 would leave 8kw. I Run this aircon all night and i consume about 4 kw during the night.
Less if in ECO mode.
I got now 2 LifePo4 banks, one is 24v 200AH the other is 24V 280Ah, Neither one is connected at the
time since i just got the BMSs and havent wired anything.

thank you that answered a lot of my questions....

 

[gnoeld]

I could use some input on this
I have 12 100A 12V Lead Acid "Everlast" batteries wired for 48 volts. 6 250 watt panels and some junk flex panels on 2 CC 150/60
I installed a Pioneer 20 Seer 115 volt Mini. What can I expect for performance?

 

[chrisski]

I could use some input on this
I have 12 100A 12V Lead Acid "Everlast" batteries wired for 48 volts. 6 250 watt panels and some junk flex panels on 2 CC 150/60
I installed a Pioneer 20 Seer 115 volt Mini. What can I expect for performance?

I recommend you start your own thread on this.

Your 250 watt panels may produce 3–8 kWh total per sunny day based off season and location. A 10% charge limitation to a battery means less maybe 6 kw can be produced, regardless how many panels are used.

Power audit is a big unknown.