Can I run A/C on solar?

Running A/C on battery power and having enough solar to recharge them is a significant investment.

First, most people who do it swap out their rooftop air conditioners for mini-split units or window air conditioners are the power requirements are significantly less.

Second, you’re looking at a sizable battery bank. Here’s the basic math. A rooftop air conditioner will run at 11-12 amps at 120 volts. Converting that to watts is 12 amps * 120 volts = 1,440 watts. Now, figure on efficiency losses in the inverting process and you’re looking at 1,800 watts per hour.

A lithium 12v battery with 100 amp hours gives you approximate 1,200 watt hours of power. So simply to run the air conditioner for an hour, you need 1.5 of these batteries. Multiply that by the number of hours that you want to run the air conditioner without sun and that gives you your battery bank size. And don’t forget about your other loads- fridge, lights, fans, appliances, etc.

I mentioned the inverter. You’ll need a minimum of a 3000 watt inverter. You’ll help your system start the air conditioners by adding a computerized soft start on the air conditioner.

And this is just to run them, we haven’t touched on the solar needs to replenish them. You need enough that you can recharge the batteries + supply excess in order to run the air conditioner without depleting the batteries while they’re running.

It can all be done. I’ve built a 600 amp hour battery bank at 48 volts using DIY lithium cells. This is essentially the equivalent of 24 of the 100 amp hour 12v batteries I mentioned above. I then have a pair of 5,000 watt inverters to power everything. Because I opted for 48v, I need a couple of different step up/step down converters to keep the existing 12v system happy for my lights, slides, furnace, etc.

And then there’s the wiring; oh lord, I have probably pert near $500-1,000 in wire alone, plus fuses, switches, panels, and all the things.

I have about $6-6,500 into the battery setup, $5,000 in inverters, and another $2,000 or so in miscellaneous accoutrements.

Those costs don’t include solar yet. I’m budgeting $3-5,000 for 4,000 watts-ish of solar. I do expect to be able to run fairly indefinitely on solar + batteries when I’m all done.

I’ve saved money by doing it all DIY. I saw a similar system that has a $40-50,000 price tag by a professional installer.