RV Solar Part I – The Discovery Process

Harnessing the sun is a beautiful thing

It’s a cold winter day here in S.FL we’re generating power from the sun. As a self-confessed geek I find this outstandingly cool and for the past 5 days we’ve been glued like little kids in front of the solar charger display, oohing and aahing over the power coming in. We’re now ready to hit the road and live “off the grid” in the best of ways, but it took us a fair few months to get to this point. So, these next few days I’m going to take you aspiring solar RVers on our journey so that you too may one day enjoy the fruits of the sun. We’ll start with the discovery process, then the equipment and end in grand style with the installation. So, here we go…..

Why Go Solar?
First things first, solar (for most people) is not exactly a cost-saver. Everyone likes to think it is, but given the price tag (anywhere from $1500 to $6000, depending on number of panels, equipment and installation) the return can take a good few years to make sense financially. If you use mainly private campgrounds or just do the rare day of dry-camping, the good ‘ol generator will do just fine. If, however, you like to go “off the beaten track” on a regular basis solar can be a definite bonus. We like a lot of spots that don’t offer electricity, and we love the idea of being self-sufficient and not having to run the generator. And, of course…it’s just so very cool….

How Many Panels Do I Need?
The first question most people start with, is how many panels do I need? Panels are expensive and you can’t expect to generate enough solar power cover everything (e.g. aircon’s are too big a power draw for regular solar use). The best way to estimate how many to get is to calculate your average usage (in amp hours) versus the average power you can expect to get from your panels (in amp hours). A very approximate rule of thumb is to target ~1oo Watts of solar for every 100 amp hours of battery capacity, but it’s best to do an individual assesment. Most RVers want to be able to use their computers, lights, appliances and maybe TV/satellite, but individual needs vary (by alot). Also, panels are usually rated for sun hitting directly on the panel at 25˚C, so actual power output will almost always be lower than their “optimum” rating. .  I won’t go through the individual calculations, but I’ll let you know (later) what we decided to do and I can direct you to Jack Mayer’s page for good examples on how to calculate your own needs.

The Basics of Solar = Minimizing Loss
Solar is basically about trying to convert sun power into real power. All this sounds good and dandy, but very basic problem with this whole idea is that it’s an inefficient process….in fact a really inefficient process….and everything you do along the way (adding wires, routing through machines etc.) causes you to lose some of the original power you generated. Just to give you an example, solar panels themselves are only about 15% efficient (so, of the power coming in from the sun, only ~15% gets converted, even less if the sun isn’t directly on the panels or it gets too hot or bits of shade are present etc. etc.). Then you add a wire onto that panel and you lose a bit more (wires have resistance and the longer and thinner the wire the more resistance it has == more power loss). Then you put that wire into a charger (== more loss) , then more wires, then finally into your battery. So, every step of the way you’re losing power, kind of like trying to put water through a hose with a bunch of holes in it. It’s a fact of life with solar so in order to do it right you’ve got to do everything you can to **minimize** loss. If you start off by understanding that basic concept you’ll save yourself a lot of tears and head-banging later on.

So, How Do I Minimize Loss?
Once you start reading up about solar you’ll find a lot of info (much of it conflicting) on how to do it. I’m not going to go through all the details, but what I am going to do is give you a few key basics and route you to a couple of sites that will teach you the rest. Here’s the top tips we gleamed from all our research:

  1. Buy Good Quality Panels & Go Higher Voltage if You Can – You want quality panels that have a long-term warranty, and if you can go with a higher voltage. The reason is to minimize loss. You can run 24V two times longer than 12V on the same wire for the same loss. It’s the very reason industrial power-lines run at such high voltages (often 110kV or above) = higher voltage means less loss over distance.
  2. Beware of Shade – You might not think you need to worry about a little bit of shade on your panels. After all, the rest of it is getting sun, right? As it turns out even a teeny bit of shade can cut power output by huge amounts, and putting one square of your panel in shade can sometimes lock out power altogether. So, beware of any shade from roof elements (aircon, antennas etc.) when you install.
  3. Use Thick Wires – One of the most important decisions you can make in your solar installation is using the right size wires. Wires are the pipes that route whatever power you get from your panels to your batteries. They’re often the single biggest loss point in any solar system and they’re often the single biggest mistake people make. Thicker wires will carry more power for longer distance with less loss, while thin wires can cause you to lose so much voltage that your batteries never get fully charged. The “standard” size wire (usually #10) that you get with a 12V solar system will typically be too small. You want to minimize loss to 2% or ideally 1% which means thicker wires (e.g. #6 or #4), especially for the parts of your system carrying the largest current. Higher voltage panels give you extra leeway, but you still need to think about proper size. Use tables or calculators or graphs to help calculate what size wire you need.
  4. Get a Good Controller – The controller’s job is to convert whatever power you’re getting from your panels to usable power for your batteries. Typical deep-cycle RV batteries have 3-stage charging profiles, and they are sensitive to temperature. So, you want a controller that allows adjustable multi-stage, temperature-controlled charging. If you’re using higher-voltage panels you will also need a controller that can handle the higher incoming voltage.
  5. Locate the Controller Close to the Batteries – The further your charger is away from your batteries, the more voltage you loose. You want it as close as possible (but not in the same bin) as your batteries.
  6. Use the Right Charging Profile for your Batteries – When setting your controller, look at the battery manufacturer’s specs to determine the right charging profile for your batteries. Many flooded cell batteries require a higher charging voltage (typically 14.8V) than what the controller manufacturer recommends (often 14.4V). Go with the battery specs.
  7. Consider AGM Batteries – If you can afford the switch AGM batteries have a much lower internal resistence than flooded cell batteries which means less loss getting power into the cells and a much faster charge time.

Those are the big basics. There is a lot more, as well as details pertaining to mounts, wire connections and such, but for those I’ll direct you to the experts:

  • Jack Mayers Site – Lots of good, detailed info here on Solar including using higher-voltage panels.
  • Handybob’s Site – He’s very opinionated (no doubt), but there’s lots of good info hiding here. Take time to look through the text and pictures.
  • AltE Site – This is a commercial site, but they have plenty of detailed articles written in plain English explaining how solar power works.
  • AM Solar – Another commercial site with some easy education articles.

Next, we’ll reveal our choice in equipment….stay tuned….

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We LOooVE Comments, So Please Do

  1. says

    I found your leaky water hose analogy to be very helpful. Thank you. We’ve just installed new AGM batteries and inverter/charger and the wire used is huge so we are on the right track. Soon we’ll go boondocking and monitor our usage to see how many solar panels we need. I’m looking forward to being able to boondock without the noise and vibrations of our generator.

    • libertatemamo says

      Linda…oh, how very cool!! We decided to go for the AGM batteries too and are just installing them today….I’m SOOO excited.

  2. Greg (Smitty) & Deb says

    Hope the post dental visit is feeling comfortable:)! (Nice write up)

    I’m a bit late in reading the Solap Panel section and your experience so far with your mod’s. I went up two weeks ago and picked up 4 of the Lifeline L16’s, and having some shelving mod’s made to the battery compartment to hold them. Noticed your Solar Panel section over this last weekend.

    I had a question about your experience with the combination of the solar, and driving alternator charging of your battery bank. We will have the same 800AH’s for the coach, and a new 8D CAT Maint Free for the chassis. The chassis is charged off of the echo from our current inverter/charger system.

    Our alternator is 160 Amp, and I was wondering if you knew what your alternator’s output power was? Trying to decide if I should have this upgraded to 200 Amps now. (A local place can upgrade it to 200 for me.) But have had some feedback of other CC owners that the 160 Amp alternator/regulator is up to the job of topping off the battery bank/chassis while driving.

    Any opinions would be appreciated.

    Mapping out our solar panel upgrade now, as the first owner added two 12V 55W panels. Frankly it was a poor install, and while they could keep the old two 8D Deka AGM’s topped off, they had a hard time every catching up from a lower level. For example, the wire run from the roof to the controller is with 14 GA, so quite a loss from the small 110W output.

    Currently planning on the Midnight Solar charger that Jack M. referred me too (had a good talk with Midnight Solar, and really like what I see/read about their MPPT’s.). Have not yet determined the solar panels yet, but leaning towards 5 235W 24V panels, still measureing. Know to run THICK cable runs, but the 24W also helps on that front. Enough rambling:)!

    Just was wondering about your rigs alternator output, and how well it seemed to charge your 800AH bank while on the road.


    • libertatemamo says

      Hi Smitty,

      Happy to meet ya on the blog. Looks like you’ve got alot of good plans in progress!

      As for our alternator. I’m pretty sure we have a 160 Amp alternator, but we only have 440 amp hour (total) battery bank. For that size of bank our alternator is fine. For 800AH I would probably upgrade the size. Now I should also mention that we try not to stress the alternator too much since it’s really not meant to handle major charging (it’s mostly just meant as top-off/maintenance for the batteries). If our house batteries are discharged below 70% we’ll run the generator to top them off before turning on the engine & letting the alternator do it’s job. Most of the time our solar has the batteries adequately charged before we’re ready to leave camp so it’s not a concern, but we always check beforehand.


        • libertatemamo says

          Did you read the reply? I’ve never said (anywhere) that we don’t own a generator. I’ve said (many times) that we rarely use it except to exercise it. On very rare occasion we will use it to recharge before moving the rig IF our solar hasn’t already done the job & gotten our batteries above 70%, and only the reason we do that is so as to not over-stress our alternator.

          To quote exactly from the reply:
          “Most of the time our solar has the batteries adequately charged before we’re ready to leave camp so it’s not a concern, but we always check beforehand.”


  3. Bruce Pirtle says

    Okay, perhaps this is a rhetorical question for seasoned fulltimers such as yourselves, but, we, as about-to-be newbies, are contemplating a RV purchase where the fridge is a medium sized residential all-electric appliance instead of propane powered. The standard propane range and electric convection oven are installed.

    While the 6500kw gen set should be more than ample enough to power the fridge when not on shore power, I seriously want to pursue installation of solar panels and return some piece and quiet to nature while trying to do my part of being a good steward of resources while off-grid.

    My question to you is, since you are in a larger than normal rig (40+/- ft), do you, likewise, have a residential type fridge? If so, how does it impact your power consumption while off-grid/generator? I’m looking for experience-based guidance in determining if this will present a problem with over discharge of a solar-supported battery bank or maybe its a non-issue.

    BTW, I’m absorbing your series of solar discussions and find them very informative and encouraging. Thanks for sharing!


    • libertatemamo says

      We have a propane fridge in our rig which I do prefer for boondocking. It’s possible to run an electric fridge off solar, but you’ll need to beef up your system. The fridge will need ~2 xtra batteries, plus 2 xtra panels (very, very rough estimation here).

  4. al says

    Fridge on solar is possible with some conditions:
    1) It has to be 12V fridge – not a 120V residential unit. They are expensive and you might have to consider downsizing. Typical 2-door propane unit is 6 cu.ft with 4 cu.ft fridge and 2 cu.ft freezer. One-door 12V unit that fits into this space could be, for example, $900 Novakool R4500 with volume 4.3 cu.ft which includes a very small 0.6 cu.ft freezer. So this is a compromise. With added insulation it should draw approximately 30 Ah a day in winter and 50 Ah in summer.

    2) To cover this fridge alone, you need approximately 240W flat panel or 200W tilted panel – this is the total wattage, doesn’t matter if it’s one big or 2 small panels.

    3) To be able to run it quietly on rainy days until the weather improves, you need enough batteries. Considering other electrical items, I would say at least 300 Ah total battery bank.

    • libertatemamo says

      I’d probably recommend a regular 120 V residential fridge and a dedicated inverter. The inverters are so efficient theses days that it doesn’t add much of a power draw plus this will cut down costs considerably on the fridge purchase (and allow more choice). Most RVers are running the Samsung RF 197. For us it would be a drop in size replacement if we ever decided to go that route.

      Other than that I think an extra 200 watts of solar power is about right. We’ve always estimated we would need 2 extra panels and 2 extra batteries to go residential.


  5. David & Kathy C. says

    255 days to go !!!
    We’re still looking at motor homes. The type of Full time RV’n we are thinking about is a mixture of boondocking and camp ground / RV park / Resort.
    We think we will love the boondocking so we need to buy a RV that is best suited for that.
    We will be going solar if we dig the boondocking thing. We think we may get the most bang for our buck with Entegra Coach, the Aspire or Anthem.
    Our main concern is how they are set up. Which would be best for boondocking?
    You guys have been there, doing that….
    Your thoughts please and thank you.

    Aspire: Stove & Aqua-Hot runs off propane.
    The Aqua-Hot is for the coach heat and floor and hot water.
    Everything else is electric.
    Propane tank is 11.8 gal 50 lbs.
    Pro or Con.

    Anthem: Aqua-Hot runs off of diesel right from the main tank. The Aqua-Hot is for the coach heat and floor and hot water.
    The stove and everything else is electric.
    which would be best for boondocking. Your thoughts please..
    Pro or Con.

    • libertatemamo says

      If you’re going to be doing a lot of boondocking and don’t want to be running the genny on a regular basis then I would definitely recommend a propane cooktop and stove. Electric cooking sucks a bunch of electricity and is hard to support without a generator. We love (love, love) our propane stove.

      The Aqua-Hot is a great feature and I don’t think it matters much what the fuel-source is? Don’t know enough about them to say more since we don’t have one in the coach.

      Are the fridges electric only? My preference is a fridge that can run propane when you’re not hooked-up. It’s possible to boondock with electric fridges, but you need a lot more solar+battery if you don’t want to be running the genny all the time.

      Also think about tank sizes. The larger your water/black/grey tanks the longer you can boondock without dumping.

      Lastly think about rig size/weight and clearance (from the ground). The more nimble your rig the more remote you can get.

      Good luck with your choice and plans!


      • David & Kathy C. says

        Just checking with the experts. ( We LOVE your Blog )

        I think I read somewhere in your blog that you were thinking about getting a electric fridge and that you would need to bump your solar to 800 watts and add two batteries. That’s probably were we will need to start. The fridge is electric. I read one blog were the guy ran his genny 1 hour in the morning and 2 ½ hours in the evening, I don’t know what that would cost but I thought it was excessive.

        I figured that we would need to run the genny for the microwave / conviction oven and there is no oven in this “Big Pig”. We all ready bought a Webber Jumbo Joe and I plan on wearing it out.

        I guess I can’t think of propane as a hassle, I will need to think of it as my friend.

        Tank size is a concern and at this size 80 / 52 / 52 seems about average. There are a lot of tips on how to keep the gray and black water even steven. The wife loved the tip on showering at the dump station. She thinks you could write a book, we both like your writing style.

        Rig size/weight and clearance is a concern. I can’t get away from the size and floor plan of this Big Pig 44B,it has captured our hearts. I watched my dad trade there RV for a bigger one, then a wider one to a smaller one and then back to a bigger one. We had a 21’ American Clipper once upon a time so were not 1st timers but we definitely lack your experience. Our toad is a Jeep 4×4 Grand Cherokee and we have our walke talkez to get us over the rough stuff. We know we will be limited :( but I have a shovel, LOL
        Thanks for the feed back
        Dave & Kathy

  6. Reed Cundiff says

    Have been following two Australian and one NZRV/caravan. For some reason they really do not like to use propane and do a lot with solar. Many use use semi/split (heat pump) for air conditioning and heating, Stirling cycle refrigerators (residential), flash water heating for showers etc. We have enough solar and LFP batteries to run the Dometic fridge during daylight hours. We leave the Dometic on over night if we know the next day will be sunny. The batteries are down around -3000 W-hrs by morning when we do. However, we are usually fully charged by noon in mid-summer and early afternoon the rest of the year.


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