Can you run an AC unit off solar power for your Skoolie? You'll be surprised on what we found out in our research.
There's nothing worse then travelling in your escape pod during the summer and spending time in a climate that can get miserably hot without a way to cool down. Even if you've installed a couple of good vent fans and treated your roof with a UV reducing elastomeric paint, you just can't beat the heat without a way to create cool air inside your Skoolie (or other escape pod of choice).
A short Skoolie at The Bus Fair in Oregon charges off the sun during the event.
A question I commonly get asked is, "How many solar panels do I need to run an air conditioning unit?". For the longest time I used to answer that question by explaining that you would never have enough solar panels or a big enough battery bank that would fit inside a school bus conversion that would be able to run an AC unit. But, in doing some research on this article I tapped on Garret Towne, President of AM Solar to give me the technical details behind why you can't but was shocked by his reply. Here's what Garret had to say:
"When someone mentions that they want to run an air conditioner I tell them they will need at least a 3000VA inverter and 200Ah of lithium battery capacity per one hour of runtime at full power for a 15,000BTU unit.
Solar will be one of a couple charging sources for the rig, but due to limitations in the amount of power radiated from the sun per square foot on planet Earth and the limited size of a skoolie’s roof, you will never be able to park out in the desert and run a 15,000BTU air conditioner 24/7.
Here are the numbers:
For simple math, let’s say an air conditioner draws 15A of current at 120V AC. That works out to 1,800W.
If you run it for an hour, that is 1,800Wh or 1,800Wh / 12V = 150Ah. I tell people they need 200Ah because not all lithium batteries can safely discharge their full rated capacity, and because it is likely that there will be other loads running at the same time. I recommend Lithium, because lead-acid batteries have voltage sag and a battery bank large enough to run an air conditioner for a substantial length of time would be impractically heavy.
Also for simple math, let’s say a solar panel produces 3Wh per day per 1W of rated output. This number varies depending on latitude and weather, but 3Wh per day / 1W is a pretty close approximation.
One hour of air conditioner operation would require 1,800Wh divided by 3Wh/day per 1W = 600W of solar left in the sun all day.
A 170W solar panel takes up about 11 square feet. 600W / 170W x 11sf = 39 square feet.
To run the 15,000BTU air conditioner for 24 hours with no charging sources, you would need 3600Ah – 4800Ah of lithium capacity.
To run the 15,000BTU air conditioner, continuously, from solar, you would need a battery bank large enough to serve as an energy buffer from peak production hours through the night, roughly 3000Ah and a 14,400W solar array. The solar array would take up 936 square feet.
If your roof mount array was 8 feet wide, your skoolie would need to be at least 117 feet long.
You can run an air conditioner for short periods of time, but you will need to plan to hook up to shore power, run a generator, or use an alternator charge to help your solar array top off your batteries in between uses. Of the rigs I’ve dealt with where air conditioning is a major concern, they have had between 400Ah and 1800Ah of lithium battery capacity.
It's also worth mentioning that in testing we've seen impressive results from alternator charging systems. One we tested got 129A at idle. That’s the equivalent of roughly 2000W of solar panels."
I had to read over that a few times before the numbers started to click for me and a visual image started to form. While it IS actually possible to run an AC off of solar panels and a battery bank, it's not for very long due to the lack of square footage needed for panels and batteries to make it happen.
Hypothetically if you had a 117 foot long bus and a big enough lithium battery bank, equipment pricing alone for a system with a 3000VA inverter kit, 3600Ah lithium battery kit, and 80x 170W solar panels, along with other system essentials would work to roughly $90,000. Not really the coin that many of us have on hand. Unless you're friends with Oprah? "And you get solar! And you get solar! And you get solar!"
An impressive and massive power bank by Broccoli Bus as displayed at The Bus Fair
An alternative to an AC unit that I just learned about the other day is an RV swamp cooler or evaporated cooler made by TurboKool which uses very little energy. Granted it would only work in dry climates due to how swamp coolers are designed and a little looking into I learned it uses on average 10 - 15 gallons of water per day. My bus only has a 30 gallon fresh water tank so for me that's not really an option unless I knew I was close to a fresh water tap that I could top off each day.
Another alternative that I've used now for a few summers and like is the Icy Breeze Cooler that also acts as an air conditioner and runs off 12v or 110v, draws very little power and circulates the icy cold cooler water through a "radiator" and uses a fan to blow out cold air with an adjustable "elephant nose" to point it where you need it.
If you're looking to invest in solar for your bus conversion, van conversion or other escape pod, the crew at AM Solar (an employee owned company) are a great resource to reach out to with questions. They also now offer solar kits for Skoolies that are designed around three types of needs. Weekend warriors, those who want a little more juice and be out a little longer and those looking to full time.
AM Solar Skoolie Kits
Short Bus Kit
340W 200A 220AhAGM 500VA
680W 200A 400AhAGM 2000VA
Full Timing Bus
860W 200A 600AhLi 3000VA
AM Solar Skoolie Kits
Short Bus Kit
Full Timing Bus
If you're interested to read more articles that the president of AM Solar, Garret, has contributed you can do so here:
Articles By Garret Towne
Solar Sunday Ask the Pro: Garret Towne of AM SolarYour big off-grid solar questions, illuminated. Ever feel like harnessing the sun's energy is more magic than it is science?… Read More
Poly, Mono, Thin film, Back contact, etc. What panels do I buy?There's more then one type of solar panel... How do you choose the right panel? The short answer:Forget all that… Read More