Solar RV Air Conditioning – Financially Frugal or Folly?

Background and Setup:

Jason and Nikki Wynn recently proved that, yes, with a specialized setup, you can absolutely have Solar RV Air Conditioning! The definitive proof is here, in their video.

The catch being that The Wynns have a VERY high tech (and therefore VERY expensive!) solar setup on their RV. They’ve gone into tremendous (and extremely helpful!) detail on the cost of parts and installation on their RV in this post on their website. The cost of their solar installation (6 panels, Solar Charge Controller, 700ah of Lithium battery cells, Inverter, AutoGenStart, Battery monitoring kit, Inverter Remote) was a whopping $16,352.74!

Nikki and Jason demonstrated that with their solar installation supplying 85% of it’s listed potential,  the Air Conditioner had only about 30-35ah net draw from the battery bank. The question on my mind is this…they have proven that it’s entirely possible on a technical level to run your Air Conditioner off a specialized solar set up…
…but is it cost effective?

How much does it cost to run a generator?

A quick look around the internet (Gas buddy and other places) reveals that the cost of gasoline has averaged about $2.95 per gallon over the last 10 years. Checking my Onan Generator Manual, I find that the Onan 5500 watt generator will use 0.6 Gallons of Gas per hour when running one Air Conditioner, and will use 1 gallon of gas per hour when running both air conditioners. This means that the cost to run a single Coleman Mach air conditioner using an Onan generator has averaged $1.77 per hour over the last 10 years.

Note that this figure also has implications when it gets warm and you don’t have solar, and you’re deciding between WalMart/Love’s or paying to ‘day-stay’ at an RV park with a power pedestal…even at $4/gallon, boondocking someplace while running the generator to power both Air Conditioners for 10 hours is still more frugal than a $40 RV Park stay.

…but I digress…

How long could The Wynns run Solar RV Air Conditioning?

Jason and Nikki’s battery bank is a 700 amp-hour Lithium LYP Battery bank. They have their charge controller set conservatively to allow them to use 70% of the power from the battery bank (500/700ah used). The LYP battery design, however would allow them to safely discharge the batteries to a 90% drained state (630/700ah used) with no damage.

Jason and Nikki have 960 watts of tiltable solar panels on the roof, and they state in their tech post that this panel setup could supply 54 amps inbound when it’s running at 100%. In the video, it’s supplying 43 amps to their battery bank, meaning it’s running at about 79% peak (idealized) capacity, and the same panel shows that they have ‘banked’ 290 amp hours for the day. Not bad for a sunny day in January!

The Coleman Mach Air Conditioner they have is pulling 76-80 amps when the compressor is running and the unit is cooling, and 27 amps when the compressor is off and only the fan is running. That’s important, because Air Conditioners don’t run their compressors 100% of the time except in the most brutal of conditions. They cycle off and on to keep the coach at a pre-selected temperature, and even when they’re on, the compressor will often cycle on and off to prevent icing in lower temperatures or other specific conditions.

The net draw from the battery bank with the compressor running and the air conditioner cooling the coach is shown in the video to be 36.3 amps.

If we presume that they shot the video around halfway through the day, we can safely presume that they’ll be able to bank another 290 amp hours before sundown, for a daily ‘break even’ total of 580 amp hours stored sunshine for the day.

Daily 580ah solar in divided by 80ah Solar Air Conditioning Draw out means that Nikki could theoretically stand on that kitchen chair for 7h 15m per day with the air conditioning compressor running a 100% duty cycle (always on and cooling), and they would break even on the power stored and used.

If it weren’t particularly hot, and the A/C were only on a 50% duty cycle… Theoretically they could potentially run the air conditioner 14.5 hours per day.

How Does That Compare To Running A Generator?

In extreme (100% duty cycle) heat, running a single Coleman Mach air conditioner 7.25 hours per day means the generator will use 4.35 gallons of gas – at a recent historical average of $2.95 per gallon, the generator will cost $12.93 per day to run.
In moderate heat (50% duty cycle) running a single Coleman Mach air conditioner 14.5 hours per day means the generator will use 8.7 gallons of gas, which will cost, on average, $25.86 per day.

We’ll presume that the average temperature (and duty cycle) for air conditioning will lie somewhere between those two points, and that it would cost $20 per day on average to run the generator to provide AC for the A/C.

How Do The Numbers Shake Out?

Cost of Jason and Nikki’s Solar Installation: $16,352.74
Number of days requiring air conditioning to break even @$20/day: 817.6 days.

At first blush, that seems like a VERY long time, presuming you would ever get to that point without having to replace some expensive parts, like batteries or solar panels.

HOWEVER…

If you were to elect to use your newly found Solar RV Air Conditioning Freedom and decide that you don’t have to chase 70* to keep cool the way you have in the past, and that meant you were to run the air conditioner 180 days per year, a $16,000 solar installation capable of running the coach air conditioning pays for itself in eliminated generator fuel costs in a little over 4.5 years!

Conclusion – YES!

It appears that not only is a specialized solar set-up technically capable of powering a Coleman Mach air conditioner in most climates for the bulk of the year, but it further appears that it is Financially Frugal and NOT Financial Folly to do so!

This seems like a terrific option for people who

• Have 60-80 square feet of unshaded roof space.
• Have a pile of money that they can spend on a longish return investment.
• Would use Air Conditioning at least 180 days per year.
• Are exceptionally happy with the RV they currently have, and are unlikely to move coaches.

Note: This entire article relies on some amount of theoretical extrapolation of provided real world values, and that it further hinges on the fact that The Wynns have not yet talked about whether they have stress-tested their Solar Air Conditioning setup to see how many hours of Air Conditioning (at a ‘normal’ thermostat setting of, say, 70*/21*c) they can have before they reach their 70% battery drain cutoff mark on their LYP battery bank. Finally, it relies most heavily on me not having borked up the math someplace. If I did, I’m sure there will be a comment, and I can correct my error(s).