Air conditioning costs! There’s just something about extracting cool air out of the hot air surrounding you that is taxing on our off grid electrical systems. It’s really a math problem, and a pretty simple one. When you weigh the amount of power you are going to be able to produce on your RV, Van or Boat against the power demands of constantly running an air conditioner, most people will find they just come up short.
Sometimes it is as simple as not having enough space for adequate solar. Sometimes it’s just financially out of reach when you realize how much equipment is involved. Luckily, not everyone’s climate control needs are identical, so over the years I’ve started my own classification system. Off grid air conditioning now comes in 3 forms: the sandwich system, the sunlight system and the unlimited. Let’s explore.
The Sandwich system - This is the most common form of off grid air conditioning my customers get. It’s enough power to make, and enjoy, a sandwich with the family in climate controlled comfort. It can be scaled up a bit to last longer, but essentially any sandwich system is going to be a one way street towards a dead battery. Sandwich systems have the equipment necessary to turn on an AC, but the solar and battery bank are inadequate for continuous operation. Some of the highest performing sandwich systems can offer numerous hours of sandwich making in comfort. I have yet to install a system in a mobile deli, so I feel like the limits of the sandwich system are still being defined.
The sunlight system - I subscribe to this category in my personal RV. Sunlight systems are fairly self explanatory. If you have sunlight available for harvesting, you can run your AC. If you have limited, poor or no sunlight, sunlight systems suddenly become sandwich systems.
Sunlight systems take advantage of the fact that it is almost always cheaper to produce power, than to store power. So they go with a relatively small battery bank to save costs, but install a very large solar array that is designed to directly take over loads during daytimes hours.
This is actually what I have on my personal RV. With a robust 2100 watts on the roof, and a comparatively small 400ah’s @12 volt battery bank, during sunlight harvesting hours I have unlimited use of my air conditioner, but as the sun sets or the clouds roll in my sunlight system suddenly becomes a sandwich system. I feel like there’s a joke about making a midnight sandwich hidden in here, but let’s move on to the last system.
The Unlimited system - That’s the true dream; travel anywhere in climate controlled comfort powered by renewable energies produced on your own little adventure rig. This is something I’ve offered in very limited quantities over the years, simply because there’s a lot of problems with making the unlimited system a reality. Assuming money is no object, there’s 3 main parts to this problem:
The amount of energy you need to store to run an air conditioner 24 hours.
The limited amount of daylight you have to produce that 24 hours worth of energy.
The limited amount of solar real estate you have on your Van/RV/camper/boat.
I have spent plenty of time trying to figure out how I can articulate a concise explanation of just how air conditioning power demands can spiral out of control, but I have come to the official conclusion that a spreadsheet is much easier demonstration. So I have made a simple spreadsheet to calculate daily demands of an air conditioner on an off grid system. Obviously every line in here is theoretical, and is really only designed to talk about running a single appliance on an electrical system that has 100% efficiency at everything it does. Basically, this is just a fun toy to demonstrate air conditioners are hard to run and shouldn't be considered any kind of official way to spec your system.
Directly below you will see the spreadsheet filled out for a standard, 13,500btu RV rooftop AC. If you download the form and fill out the wattage of your AC, how many hours you'll run it each day, and the estimated duty cycle of the AC, (in moderate weather it may only cycle on 20% of the time, in a heat wave it may run 100% of the time), the spreadsheet spits out your consumed watt hours per day, as well as turns that into an amp hour rating that factors in your battery's maximum depth of discharge.
The three lines regarding solar harvesting hours, array output and battery depth of discharge are set up for an average, flat-mounted array, on an average day, with a lithium battery bank.
As you may have noticed, having such a massive electrical load like this RV AC, running around the clock, and only having 6 hours a day to replenish all that power, makes for some pretty colossal solar system demands. Unfortunately, there's really only two ways to make this situation turn more in your favor; reduce your power needs, or increase your power production.
Insulating your rig, raising the thermostat level or using a lower wattage AC are all ways to reduce your electrical demands. On the other end for increasing production, if we're out of space for additional panels than removing partial shading obstructions on the roof or adding tilting can help increase how much power we can harvest from the array every hour. Beyond that, there's not a whole lot we can do to improve the colossal amount of a power an air conditioner needs. Higher efficiency air conditioners, like the mini split unit I installed in my rig, definitely make a difference, but it's still a lot of power no matter how you look at it.
Alright, to sum all this up. I feel like I should show some images of an Unlimited system. Say hello to the rolling power plant that was put together back in 2019. With 4410 watts of solar between the roof and a custom built awning, 800ah's @24 volts of batteries and a 5000 VA inverter, this client can run his AC and other accessories around the clock. Let's not kid ourselves though, even this colossal system sometimes need some help from the onboard generator when the clouds roll in.