Monday, September 25, 2023


Good solar design will meet most RVers’ needs

Solar power has been around for years, but during the past decade or so solar systems have become popular equipment for RVs of all sizes. You must design a system that will meet your needs. Solar is not a magic word for free power. You need to first calculate your energy needs, then design a system that will meet those needs.

The first thing to do is define the load requirements of whatever items you will be running off your batteries. Remember that it’s the batteries that really run the electrical loads while the solar panels are merely a source to help recharge them.

When we run any 12-volt loads such as lighting or water pumps, we are drawing amp-hours from the batteries. Whenever we run 120 volt AC items we will be running these items through an inverter, which converts battery power to AC power. We need to find the wattage of each item.

The next step is to calculate how long items will be operated. The longer time equals more amps they will take from batteries. The intention of a solar system is to run the generator once daily to recharge the batteries to operate various items.

Solar panels only work when the sun hits them. If you’re camping in Arizona you’ll get more output from your solar system. But if you are camping in the north woods during the rainy season the output is reduced.

Solar panels also need to be at a right angle to the sun’s rays for maximum performance. Most RV installations are flat mounted. Even at noon the sun is never directly overhead so there is some loss, and early morning and late afternoon may only give you 25 percent of the performance that you are expecting.

Keep in mind when doing calculations that there are variables to consider. Sunny Arizona versus the rainy Pacific Northwest is one of them. Also, the brand of solar panels makes a big difference. Some panels result in decent output in low light conditions while other brands rapidly fall off when the light isn’t perfect.

A good place to learn more is at AM Solar in Springfield, Oregon.


Chuck Woodbury
Chuck Woodbury
I'm the founder and publisher of I've been a writer and publisher for most of my adult life, and spent a total of at least a half-dozen years of that time traveling the USA and Canada in a motorhome.


  1. IMO, doing the calculations for sizing a solar system is great for determining the MINIMUM setup needed for expected weather conditions, but MORE solar panels and battery storage is always desirable to keep things running when you’re operating at the assumed limits or beyond. Some folks have setups and camp in environments and conditions that will always keep their energy needs easily topped up while other camper’s setups will never have enough given the needs and the places where they travel. A man’s gotta know his expectations and his limitations…

  2. I think a lot of “over-thinking” is done on this solar stuff. I’ve never counted up any watts or amps. I just put a bunch of solar on the roof, had an MPPT controller installed, have two golf cart batteries, and life is (and has always been) good. We run our Dish box all day (for the music, believe it or not), keep at least one roof vent fan on in warm weather, and never experience any problems, rain or shine, blue sky or cloudy days. I know many will not agree with me, but this is OUR experience. We also have an old Cobra CPI 2550 inverter that powers my wife’s hairdryer, and that’s about it. We never use the nuker, but it will run if we actually needed it. The inverter also runs a small Harbor Freight electric water pump for use when we want to transfer fresh water from two six gallon spare containers.

  3. It’s a good article. When the author states that you must design a system to meet your needs, it is really important for the RV owner to be really honest and realistic about their usage needs. People can spend a fortune on solar installs and additional batteries unnecessarily. For those like myself, who enjoy “getting away from it all” for a week or so at a time my single 160 Amp/hour battery and 160 Watts of portable solar do a great job charging the battery to keep my fridge working on propane and running lights and the water pump when needed, as well as recharging my cell and tablet. We travel extensively in our RV, (not really full-timers) and dry camp mostly for 3-4 days at a time (which is enough for us at one time) and wanted to let others know that you don’t need to spend a fortune for solar if you don’t need really need it.

    • >you don’t need to spend a fortune for solar if you don’t need really need it.

      True, especially when augmenting with alternator/generator charging.

  4. Solar on an RV is nothing more than a battery charger. If you want to run more stuff, get more batteries. Rule of Thumb: 100w solar per battery. Another ROF: You’ll get about 5 hrs / day of usable sunlight, so for a 100 watt solar panel that is rated at 5 amps, your 100w panel will give you about 25 amp hours of juice to recharge your battery bank. Now you can calculate your loads and see how many batteries (amp-hours) you will need. For typical lead-acid flooded batteries, which should not be discharged more than 50%, you should cut their rated amp-hour capacity in half.
    Oh, and use big wire (#4 AWG or larger) between your solar combiner box and charge controller and battery bank.

    Solar is great, but you must live within your means (amp-hour wise) or you will be buying batteries to replace those you have damaged by over discharge.

    • Hey Bill, I like how you cut the BS out of it. Most solar uses I believe is to extend your boondocking stays, not put you on a solar grid to use your Kurig. Like he said be wise, be smart about your power use and known demands and live life in the simple lane.

      • We are full-timers, have solar, and boondock 95% of the time. Yup, I even run my Keurig. We have four 360 watt panels and two lithium batteries, along with all the components necessary to make everything run smoothly. I love our free power!

      • Bill’s input is correct, though that doesn’t mean that additional information would be BS. It is a human trait to want simple answers even when none exist.

    • I agree with the post in general. I’ll chime in on some details for geeky onlookers. 🙂

      > Solar on an RV is nothing more than a battery charger.

      i understand the point, but I think it’s misleading. Consider what happens when one adds a load to the system and Vfloat and current are unchanged.

      > If you want to run more stuff, get more batteries.

      Getting more battery than one can charge fully and regularly is a recipe for lead-acid battery murder.

      > You’ll get about 5 hrs / day of usable sunlight,

      Insolation maps will show interested parties the average Full Sun Equivalent (FSE) for their area and time of year. It’s knowable stuff.

      > your 100w panel will give you about 25 amp hours of juice to recharge your battery bank.

      Temperature derating is a critical part of the equation.


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