Estimating off-grid battery life based on HVAC and solar use

I think it depends a great deal on circumstances: how much solar you’re getting, how long you run the HVAC, and how big a temperature differential you’re asking the HVAC to overcome. If it’s 95° outside, are you asking it to cool to 68°, or just down to 80° to take the edge off the heat?

I did a test yesterday to see how much battery we’d use in a day. Due to mild temperatures—low 70s during the day and 50s overnight—we used only the fan portion of the HVAC system to circulate air and remove humidity, with windows open during the day. We used a Crock Pot for dinner, so we didn’t use the oven or cooktop.

For most of the day, we were using around 500–600 watts but generating almost that much solar, so the Energy console showed net consumption of 0–150 watts for most of the day. The battery stayed at 100% for several hours. Overall, we used about 15% of the battery in 24 hours.

I wouldn’t put too much faith in extrapolating from a single day, but you might make it 5–7 days under favorable circumstances if you manage power usage. However, somewhere hot where you’re really cranking the AC to bring 90°+ temperatures down to a comfy 70°, I wouldn’t be surprised if you went through the whole battery in a day or two—especially if you use the cooktop or oven a lot, since those draw 1–2 kW depending on power settings.

Personally, I’m happy to be able to run the AC on battery at all; that wasn’t even an option in my old trailer!