How much solar to run an air conditioner?
In another page, we look at running an air conditioner from a lithium battery. Here we look at how much air conditioner time a certain amount of solar will give you. If you have more or less solar than this example, just extrapolate the figures from here.
Let's take a look at how much solar is needed to keep up with the power draw of 62 amps per hour required to run our example air conditioner from a 400Ah lithium battery.
We'll start with the premise that we don't want to drop the battery capacity below 50% because we need some power after the sun's gone down for the coffee machine and air fryer.
We've worked out that the air conditioner will use up 62 amps to maintain the temperature for one hour. We have a 400Ah lithium battery and 400W of solar providing power.
So you could run this air conditioner for roughly 5 hours using 400W solar and half your 400Ah lithium battery. But keep in mind that you have other items to power and you need to replace that 200Ah you've used at some time.
If you had double the solar than the above example, ie 800W, you could run this air con without any drain on your battery!
If you had 1,000W (1kW) of solar, you would have plenty to run other appliances at the same time, as well as recharge the battery.
No all rooftop rattler air conditioners are this energy efficient. Some will use 100Ah per hour continuous running, but if the van is well insulated, the windows have insulated shades and the van is reasonably sealed up, that could be reduced to a 50% run cycle and 50% where just the fan is running, which requires a lot less power. The battery would be recharging from the solar during this fan-only part of the cycle.
We've put together a simple formula based on the advertised capacity of a solar panel, and other factors such as geography and time of year, so that you can work out how many amps your solar should be harvesting to charge your battery.
How much solar to recharge your battery?
It's obvious that you need to replace what you use, but the health of a lead acid battery actually requires you to replace more than you use. A lithium battery needs you to replace what you use and does not need to be maintained at 100% state of charge. It prefers to work.