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Ask Dave: Can I run my roof AC on solar?

Answers to questions about RV Repair and Maintenance from RV expert Dave Solberg, author of the “RV Handbook” and the managing editor of the RV Repair Club. This column appears Monday through Saturday in the RV Travel and RV Daily Tips newsletters. (Sign up for an email reminder for each new issue if you do not already receive one.) Today Dave discusses running a roof AC on solar.

Dear Dave,
I have a 2004 Fleetwood Providence. What type of solar system would I need to use one AC and regular electric outlets to boondock for a week or so? I have 4 AGM 6-volt batteries now. Would I need to change them or get more? —Randy

Dear Randy,
Until just recently I would have said there is no way to run a roof air conditioner on house batteries through an inverter. Not only would it take a gazillion AGM batteries and a football field of solar panels, but the initial startup of the typical roof AC is too high.

Enter SoftStartRV™, lithium batteries, and high-watt solar panels. Once again I was reminded to never say never! At the recent RV Show in Hershey, PA, Keystone unveiled their new SolarFlex system that will be standard on all Keystone products.

The SoftStartRV has been featured quite extensively by RV Travel and especially by Mike Sokol. According to their website, it will reduce initial startup draw by 70 percent, so you can actually run two roof AC units at one time. It reduces both torque and startup power and reduces the thumping a roof air conditioner typically makes during the cycling on and off process. I’ll let Mike dive into the technical aspect, however. Check out the video in this article on installation.

Lithium batteries

It’s amazing how technology has changed, especially when it comes to RV batteries! With several companies getting their start in the marine industry, we see the migration into the RV world with high amp hours and more affordable prices. However, they’re still several times more expensive than traditional lead acid batteries.

Keystone has partnered with Dragonfly Technologies, that has been known for their Battle Born products the past few years. They offer a 270 amp-hour battery with battery management system, as you cannot just drop lithium batteries into your existing system without the proper charging system. Once again, Mike Sokol has some great information from Progressive Dynamics in a livestream here.

The difference is lead acid batteries can only be drawn down to about 50 percent, while lithium can be drawn down 95% or more. There are many more advantages to lithium batteries; however, I’ll refer you to Mike’s articles. While working with Zamp Solar, I was introduced to Expion Batteries, which the former owner of Zamp Solar had started up recently.

Solar panels

When I was traveling around the country for Winnebago training dealers, solar panels were a novelty mostly for the Blue Bird Bus owners. They were the size of a king size mattress and took forever to charge a single group 27 battery. Fast forward a few years and solar panels have gotten smaller, lighter, and more powerful.

This picture shows two 300-watt panels on the Keystone displayed at the Hershey RV Show. Keystone partnered with Future Solutions to develop a series of solar arrays that they use on various models. They offer 200-watt and 300-watt panels that can be combined to get more than 1200-watt charging power! So, it is important to understand the charging power available, amp hours of your batteries, and power requirements of your rig, as you will be using items that will draw power other than just the roof AC. You need to have the right battery management system.

Having said all that, the unit at Hershey had a Bluetooth monitor. The rep from Keystone pulled up the screen on his tablet that showed power consumption as well as projected battery/amp hours available. The unit with the roof AC running could last approximately 2.5 hours. And that was with three 270 amp-hour batteries

So, after all that, to answer your question. It can be done, but not for a long period of time and at a fairly high cost.

Read more from Dave here

Dave Solberg worked at Winnebago for 15 years developing the dealer training program, as marketing manager, and conducting shows. As the owner of Passport Media Creations, Dave has developed several RV dealer training programs, the RV Safety Training program for The Recreation Vehicle Safety and Education Foundation, and the accredited RV Driving Safety program being conducted at rallies and shows around the country. Dave is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.

HAVE A QUESTION FOR DAVE?

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Bob P
1 month ago

This is similar to EVs, they work fine for a short distance but then it’s time to recharge for a longer time than refueling an ICE. Battery power is the future, just not the immediate future.

Firefly
1 month ago

As you point out, the issue isn’t supplying the draw, but in having sufficient battery capacity to have an actual cooling effect. And how do you recharge those batteries? By parking in the sun, which is why your RV is so hot in the first place. I have 600ah and 780w and don’t bother running my AC off batteries because of this.

Last edited 1 month ago by Firefly
Mike Sokol(@mike)
1 month ago
Reply to  Firefly

One of the ideas I’m working on is designing a large foldable solar array that can sit out in the sun while your RV stays much cooler under a shady tree. I think it needs to be at least 600 to 800 watts of solar to be useful for boondocking.

Matthew R L
1 month ago
Reply to  Mike Sokol

You do not need foldable panels to do that. I have 8 100 watt silicone crystal panels that I keep stacked inside and carry outside in the morning.

They are 2 × 3 feet each and easily manageable. Total storage space is about 6 cubic feet.

In full sun of direct sunlight, I get 98 watts per panel. But you will only have about 75 watts of useable power due to controller and inverter inefficiencies. So altogether I have 600 watts of useable power.

I do not have an AC unit, so I cannot test the theory. But a 5000 BTU air-conditioner pulls about 500 watts so it is easily doable.

However, on a partly cloudy day, I only generate 56 average useable watts per panel per hour so calculate that in. Your air-conditioner will cycle on and off on a cloudy day, so the power usage may balance that out.

The total solar panels, controllers and wires cost me $1200. And you will need to figure in your batteries and inverter.

The air-conditioner will jump to a sudden surge of up to 2 kilowatts momentarily upon startup. So you need a high amperage inverter with a battery bank that can handle that without dropping below 11 volts. I use a 2 kilowatt inverter because it provides the same power as an electrical socket in your house and I can run anything on it that one would normally buy for a house.

The other thing is shadows from trees. I have to keep an eye on the panels and go out and move the panels 5 or 6 times a day to keep them in direct sunlight. So plan on that if you have trees.

Tommy Molnar
1 month ago

I have a SoftStart on my ac. If I was to bring my meager 2000 watt generator, it runs the ac. I tested it in my back yard. But I rarely carry my generator. I’ve upgraded to Lithium batteries and as a test, fired up my ac through my pure sine wave inverter with nothing else running. Low and behold, the ac started up! But, I don’t have enough battery power to run this setup very long, so I don’t even try. I just wanted to see if it would work. It did, and I won’t do it again. We just open all our windows and enjoy the breeze. Not in 120° Quartzsite though – ha.

Scott R. Ellis
1 month ago

That much-ballyhooed Softstart reduces *start-up* power requirements. What effect does it have over, say, a hot evening’s AC use? 10%? 2%? It might be great at what it does but what it does will make little difference to the fact that the answer to the original question is still actually “Not really.”

Irv
1 month ago
Reply to  Scott R. Ellis

Softstart has little to no impact over the course of an evening. It reduces the peak by spreading it out–it doesn’t reduce overall power usage.

tom
1 month ago

Progress at a price.

Bill T
1 month ago

Is there a real reason why you would need air condioning when boondocking? Wouldn’t it be noisy? Will you be inside your RV that much to need it? Boondocking in nature with an RV is having the ability to enjoy the great outdoors while having a comfortable tent to sleep in at night. Your own bathroom and some cold drinks in the woods, what else do you need.

Paul
1 month ago
Reply to  Bill T

We all have our own definition of boondocking. It is not always about peace and quiet in the great outdoors. It could be at a racetrack or an RV rally, or just a night or 3 in a National Forest Campground where the temps are in the 80s overnight. The answer is how much is it worth to not have to run the generator in a boondock setting for comfort. It is indeed possible to run AC off battery recharging with solar. The price is coming down.

Matthew R L
1 month ago
Reply to  Bill T

Depends whether you are boondocking in Michigan or Arizona where you are facing the desert sun and no shadetrees.