How to Make Solar Power for the Air Conditioner in an RV Work

So you’ve been on the road for a while now and you’re ready to enhance your RV to be the epitome of efficiency by adding solar power, but is it enough power for your air conditioner? If you plan on taking your rig boondocking or just want to invest in an alternative to solely battery power – solar panels may be the next worthy upgrade.

How Solar Panels Work for an RV

At the fundamental level, solar panels simply collect energy from the sun to charge the bank of batteries that powers your RV.

The batteries themselves provide a 12-volt DC. Any RV powered by a 12-volt current will work directly off the power from the batteries.

But when it comes to 120-volt AC appliances, such as an RV air conditioner, the 12V current from the batteries must go through an inverter, which transforms it into a 120V current that can power your air conditioner, microwave, power outlets, etc.

That sounds simple enough, but there are a few more things to consider when powering your RV and its air conditioner or other appliances with solar panels.

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How to Power an RV Air Conditioner with Solar

Determining how to power an RV air conditioner with solar boils down to how much power you need. This, in turn, determines the size of the components (batteries, inverter, solar panels, etc.) required to power your rig.

First, you need to determine the amperage requirements of your air conditioner. You need to know how many amps it pulls per hour to operate, plus you’ll also need to have some sort of estimate of how long you’ll want to be able to run your air conditioner.

For example: If your air conditioner runs at 150 amps per hour, you will need 150 usable amp-hours of battery storage for every hour you intend to run your air conditioning unit before recharging. At 150 amps per hour, our example AC unit would need 600 amp-hours of battery storage to operate for four hours. 

Of course, operating your air conditioner in your RV doesn’t happen in a bubble. You still have all of the other appliances and items that require power, whether they operate directly off of 12V current or 120V current from the inverter.

You’ll also need to have an estimate of how many amp-hours of power you’ll need to power the rest of your RV appliances in addition to your air conditioner. This is necessary to make an informed decision on the size and capacity of the equipment required for your particular needs.

Battery Bank

When thinking about your battery bank, you’ll want to consider how much storage capacity you need to operate all of your appliances per day and multiply that times how many days you want to run if you have no way to recharge the batteries.

If you estimate 800 amp-hours per day, but you want to operate for three days, and it gets cloudy, and your solar isn’t recharging your batteries, you’ll want 2400 available usable amp hours (800 amp hours x 3 days = 2400 amp hours).

The only problem with the math is that batteries are not entirely used to a zero-depth of discharge. That means most deep cycle batteries (whether flooded lead-acid, sealed AGM, or sealed gel) don’t allow for a full discharge. Discharging those batteries below 50 percent capacity can damage them and shorten their lifespans.

So you’ll want about double the capacity that our initial equation would indicate. In our example, you would be better off with 4800 total amp hours of battery storage to get the 2400 available usable amp hours that you need for three days.

You could also opt to go with lithium batteries, which allow for a much deeper depth of discharge without suffering damage. Lithium batteries are typically more expensive than other options. Still, they have a much longer lifespan and a deeper depth of discharge (which means fewer batteries needed), so they could be worth considering.

Inverter

Our RV air conditioning unit is likely to be a giant power hog on our rigs for most of us. So you will want to size your inverter to be able to power your AC unit.

There is an important consideration to note here. Most AC units operate at a specific wattage, but that wattage is typically lower than what it takes to start up the unit. When considering the inverter’s size, you’ll want to base it on the AC unit’s start-up wattage.

You also don’t want to simply match the start-up wattage. For instance, if your AC unit has a starting wattage of 3000 watts, you’d want an inverter that is rated at least 3700 watts or even a little higher than that.

There is the option of installing a soft start device, which would reduce the wattage necessary for starting your AC unit. This would then reduce the wattage rating required for your inverter.

For safety, it’s best to install an inverter that is rated at 700 to 1200 watts higher than the highest wattage you’ll need.

Solar Panels

Solar panels are rated in watts. So to figure out how many panels you need, you’ll first need to determine the wattage necessary to charge your batteries.

Say you need 800 amp-hours per day of battery capacity to meet your needs. If you estimate that you’ll get about 5 hours of direct sunlight to your solar panels per day, that means you need 160 amps for each of those 5 hours to recharge your batteries every single day.

Now you know you need your solar panels to generate 160 amps per hour for 5 hours, but we still need to know watts. To figure out the required wattage from your solar panels, we simply multiply the number of amps by voltage (remembering that the charging voltage on a 12V battery is 14.4V). When we multiply 160 amps by 14.4 volts, we get 2304 watts. So you would want at least 2304 watts of solar panels to get the charge you need.

If you think you’ll be off-grid for days at a time and would have a higher battery capacity but still need to charge it every few days for the same 5 hours, you’ll want to reconfigure the capacity of your solar panels accordingly. 

Do Sweat the Small Stuff

If you are building a substantial off-grid solar array, don’t skimp on the little things either. Remember to seek out the appropriately rated wiring to handle the demand placed upon it by your energy system. That goes for the wiring from the panels to the batteries and from the batteries to the inverter.

RV A/C Units are Inefficient

RV air conditioning units are not the most efficient appliances in the world. Of course, a lot of that has to do with the rig itself not being well insulated or adequately outfitted for the changing seasons. RV manufacturers are improving all the time, but most rigs aren’t what we’d call energy efficient.

Air conditioners in RVs require a lot of power and simply don’t cool well. 

An alternative, especially if you want to use solar panels as a primary source of power, is installing a mini-split air conditioner instead.

Mini-split air conditioners operate on much less power than a rooftop AC unit, are simple to install, and are relatively inexpensive to operate. They are a perfect option if you need to use your AC day and night.

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Is the Cost and Hassle Worth It?

Determining whether or not solar power is worth the cost and the time involved to assess your necessary configuration and get it installed is a difficult thing to answer.

If you want to go all-in on solar, it may be an expensive up-front investment, but it is just that and investment. Solar is a long play that will pay off over time in the lack of electric hook-ups or generator fuel that you’d otherwise be forking out dollar bills for.

Making adjustments to your plans – like installing a soft start or swapping out a rooftop AC unit for a mini-split – can lower the requirements needed for a smooth operation.

But do your homework before you jump in headfirst. The size of your rig, the length of time you plan on owning/living in your rig, etc., all play vital factors in determining whether the money and time invested will eventually pay off for you.