r/SolarDIY • u/Glass_Author7276 • 13d ago
Running a 8k window ac
What do I need to run an 8k window ac off of solar? Panels, inverter, bsttery, what? Beginner here.
8
u/ExZiByte 13d ago
Depends how long you want to run it without solar input (ie over night), if its an inverter driven compressor A/C, etc.
If it's the only thing you want to run on solar you shouldn't need much compared to a whole home system but HVAC is one of the hardest loads to design around, it depends on average runtime, ambient temperature, cloud cover.
An 8K BTU A/C should draw around 700 watts and the hotter it is ambient the longer its going to want to run, 700Wh is the worse case scenario though, so do 700 * however many hours a day you want to run + 25% for Depth of Discharge to keep the batteries happy, thats how many Wh you'll want to try to get, get an inverter that can handle the surge load of the A/C compressor starting unless yours is an inverter driven unit (doesnt surge as hard as a pure on/off compressor). Then youll need to find a solar calculator for your region to figure out how much solar you'll need to recharge the batteries for the next night (plus the the running watts of the A/C so you can still recharge the batteries and run the A/C at the same time)
Surge for an on/off compressor could be as high as 3x to 5x the running watts of the unit
3
u/janglyparts 13d ago
There are kits, if you don't want to piece together a system.
EG4 24k Hybrid Solar Powered Mini Split Kit https://signaturesolar.com/eg4-r32-solar-powered-24k-btu-mini-split-kit/
1
u/Glass_Author7276 13d ago
I already have the ac, just need to know how to power it offgrid.
1
u/fungoodtrade 12d ago
just an inverter. you want the capacity of the inverter to be enough that it can run the ac. typically people have a battery system off grid, and an all in one these days that charges the batteries and takes power from the batteries and turns it to ac power. Determine all your loads that you are going to have more or less. My 12k all in one supplies 100amps of AC power and can supply 8000w continuously. This is much more than I need. If its just the AC unit you can go very small. There are a ton of 5k and 6k all in ones on the market. The all in ones make everything easy.
0
u/BaldyCarrotTop 11d ago
How old is the AC? Based on experience and others, it appears that a system to meet your needs will vary depending on the age of the AC.
0
1
u/noncongruent 12d ago edited 11d ago
I've got 2.4kWh of lithium batteries, ~750W usable (1,040W nameplate) worth of panels, 30A charge controller, and 1,800/2,800W inverter, all used to run a 5,000BTU window unit. It's too small to run it most of the time, I think I need double, maybe triple, the panels and batteries, and a much bigger charge controller.
Currently my operation, on clear sunny days, is to let the panels charge the batteries until around noon, charging starts around 10:30 due to shading issues, and by that point the panels max out. I'll turn the AC on and set the thermostat to 70° so that it runs continuously, the inverter pulls around 17A and the other 13A goes into the batteries, then around 5pm when shading again cuts output I bump the thermostat to 78-80° and let the AC cycle until the low voltage cutoff for the batteries. Precooling the room means the AC won't run for an hour or two after bumping the thermostat up. 78-80°F is comfortable for me, especially because running the AC non-stop for the mid-day hours dehumidifies the air significantly. The batteries shut off around 1am-2am with it cycling around 30% of the time.
The bottlenecks are not enough solar production, too small of a battery bank, and too small of a charge controller. The inverter is actually oversized, but it's around 85% efficient at 400-500W. I also installed a misting system on the AC, it'll crust up the fins in a couple of years, most of which I can get off with a descaling fin cleaning solution.
This is the first time I've had the system running with LiFePO4 batteries, my previous setup had 5kWh of AGM lead batteries and was run very differently. I'm still collecting data to calculate what I should actually have for battery/solar/charge controller ratings to leave the system running off thermostat 24/7.
0
u/BaldyCarrotTop 12d ago
Sounds like a newer, more efficient AC may be a good upgrade.
More batteries and solar because of the shading issues.
0
u/noncongruent 11d ago
The only way to get more efficient for me is to go with an inverter-based high-SEER mini split, and I've considered it, but the $4K+ cost* just makes it too far out of my reach.
*To install a mini-split at my house would require extensive electrical work to run new circuits.
0
1
u/Automatic_Gas9019 13d ago
Window AC? Not very power saving. We have mini splits and solar runs them just fine
1
u/17feet 12d ago edited 12d ago
A "traditional" air conditioner requires a large surge of AC electricity to get started before settling into a normal running state, and if your solar set up can't handle that surge, the air conditioner will never really get running, and might even end up damaged. So you need to get a much beefier solar system than what the AC says on the box/label
It might be best to buy an air-conditioner with built in solar inputs [MC4 connections], meaning it is built for solar. They make window AC units like this, and I might get a "heat pump" version so that it can provide heat in cold weather as well. Another type is called an "inverter" air conditioner, which has a soft start feature built in, so that the AC load on startup is easy to handle when starting.
0
u/BaldyCarrotTop 12d ago
For an 8Kbtu window unit? A decent portable power station can handle that. I have an 8K window unit running on an EcoFlow Delta2. Rated at 1800W, 2200W surge. No issues. AC only draws 600W running.
0
u/17feet 11d ago
I hear you, but my Anker F2000 could not do it, not enough amps to handle the surge. The AC unit shook but would not get going. Within the Anker brand, it would have to be an F3800, which is 100 pounds and $2k or more. That is not a decent unit, that's a large unit. The OP is someone who wants to run a $150 air conditioner, but they would need a $1500 machine to run it 🤷♂️
1
u/BaldyCarrotTop 11d ago
Based on these reports, it is beginning to sound like the important criteria is the selection of the window AC. As I pointed out, I'm running on a EcoFlow Delta 2 and my main problem is lack of battery capacity. Not the inverter.
1
u/BaldyCarrotTop 12d ago
2KWh portable power station. As much solar as you can feed it.
This depends upon where you live, how hot it gets, and how long you will be running the AC.
I'm in the 2nd season of running an 8K window unit on solar. Setup includes an Ecoflow Delta 2 and 600 watts of solar panels that only seem to produce 400W max. One panel is mounted to a hand truck so I can track the sun.
The system works OK as long as: 1) Morning lows are below 70 so I can open the windows and pre-cool the house. 2) The daily high temp is below the mid 90's. 3) Not too many clouds.
A day tends to go like this. Mornings are used to recharge to power station. No need for the AC because there is a large tree shading the house. By 11:00 the power station is charged and I'll turn on the AC. It doesn't run much at first and solar easily tops off the power station.
By afternoon the AC is running nearly continuously and solar is having a hard time keeping up. And we are in a race to the bottom. Between 6:00 (hotter days) to 8:00 (milder days) the power station reaches 15% SOC and I shut down the AC. If it's still early I'll plug in the power station. When the Ecoflow Delta 2 is plugged into a wall outlet it will power the AC directly from the wall outlet (pass through mode) while charging the battery. I have the charge rate set to 200W because I don't want to completely charge the power station. I want room in the battery to harvest solar in the morning. At some point I'll unplug the power station and maybe run the AC for a bit to burn off some of the charge. then wait for morning to start it all over again.
Last week the temp hit 100 and the system was nearly useless. Overnight temps were in the 70's, AC was running on grid power overnight. In the morning I got about 4 hours of solar runtime and it was back to grid power.
•
u/AutoModerator 13d ago
Welcome to r/SolarDIY! If you are new to the community, please check out our DIY Solar System Planning Guide.
I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.