Does Solar Power Matter on RVs with Large Lithium Batteries?


RVs with really large lithium batteries are becoming more common these days.  It’s not unusual to see a Class B come from the factory with over 8,000 Watt-Hours of battery capacity.  When you compare the capacity of the battery to the size of the solar panels, you have to wonder… would you even notice the solar?  On a trip to Big Bend National Park last fall, we decided to find out:

 

So, the long and short of it is no… we didn’t see any difference one day to the next if we had solar panels active or not.  But like most things in life, there’s a bit more to the story to understand it fully.

First off – the rig we’re using in that video is Parky, a Limited Edition National Parks Foundation Travato.  These rigs are made with a larger lithium-ion battery pack that “regular” lithium Travatos.  And even a “regular” lithium Travato has a battery pack far larger than most traditional RVs.  It’s hard to overemphasize the battery capacity – in one of our other videos, it ran the air conditioner pretty much all day long.  Parky’s battery pack is 11,600 watt hours.

Next, realize that the gauge we’re using is a simple analog gauge that just shows our energy level as a percentage of that really large number.  It takes kind of a lot of energy to move that needle.

Also – we ran that experiment in November  when the sun (even in Texas) was fairly low in the sky.  That’s just not the best time of year for solar panels.

And finally, realize that even under ideal conditions (which you’ll almost never achieve), it would take a good while for solar power to charge that battery.  Let me show you what I mean:

  • To move the needle one percent, it would take an amount of energy equal to one percent of 11,600 Watt-hours.
  • One percent of 11,600 Watt-hours is 116 Watt-hours.
  • A 115 Watt solar panel (there are the equivalent of two on Parky), can produce  (at maximum – when clean – in full sun – at 90 degrees to the sun’s rays) 115 Watts. (surprise!)  But in real-world use, it produces significantly less.
  • So it would take a 115 watt solar panel just over one hour, in ideal conditions, to charge Parky’s battery by one percent.
  • Or – more than a hundred hours of perfect and direct sunshine to fully charge a depleted battery.

Over 80% at the end of the day is pretty good in my book. Solar or not.

Now compare that to the output from the alternator.  In other testing we’ve done, we found that while driving, Parky’s second alternator will charge the battery at a rate of one percent per minute.  Yes, per minute.  Which makes the alternator over 60 times faster than a solar panel at charging the battery.

Given all that, it shouldn’t be too surprising that we didn’t notice a difference from one day to the next with or without solar panels plugged in.

But It’s Not All Bad News for Solar Power

OK.  So on a rig with a massive lithium battery, 230 watts of solar power didn’t make much difference.  But you absolutely would not get the same result with a “regular” RV battery.  A typical 110 amp-hour RV battery might contain about 1386 Watt-hours of energy when fully charged (110 * 12.6).

It would take that same 115 watt solar panel only about 12 hours of perfect sun to charge that battery all the way.  That’s a much more noticeable rate of charge, and you might see the needle move within a couple of hours.

The Takeaway

So what do I take away from this?

Well, the first thing is that the analogy we’ve been using of filling up a swimming pool with a teacup is pretty on-target when it comes to solar power on rigs with large capacity battery banks.

The next thing I’d conclude is that – even if it isn’t a ton… you never turn down free energy.  I was only joking about removing solar panels!  So if you are considering  rigs with large lithium battery banks, and one comes with 300 watts of solar panels, and the other only has 100… well, 300 is still more than 100.

But I wouldn’t let that solar power capacity be the determining factor in my decision on a purchase.

And finally, if you’re looking at rigs that don’t have a large lithium battery bank… forget everything you saw in the video above.

(Except Big Bend National Park – that place is awesome!)



James is a former rocket scientist, a USA Cycling coach, and lifelong fitness buff. When he's not driving the RV, or modifying the RV (or - that one time - doing both at once), you can find him racing bicycles, or building furniture, or making music. In his spare time, he works for a large IT company.


    34 thoughts on “Does Solar Power Matter on RVs with Large Lithium Batteries?

    1. Wayne

      Here are a few ideas:-

      1: Measure the performance over years rather than just one day.
      2: Be more precise in your measurements.
      3: Make sure everything is working correctly and you know what you’re talking about before running the tests and sharing your results with everybody.

      Thank you for reading.

      Reply
      1. James - Post author

        I think you may have missed the point of the video and test. This was about solar ON A RIG WITH A LARGE LITHIUM BATTERY. Says so in the title.

        1. Performance of RV solar over “years” is completely irrelevant in this context. When you’re out of power, it does you no good at all knowing that in a few months, your solar array may have fully charged the battery. Further – unless you never drive the rig, the alternator will charge the battery hundreds of times over in a year of use.
        2. As we said in the video multiple times, this was intended to be a “real world” test, and not a laboratory experiment. As such, we only used the instrumentation on board. If you routinely RV with an oscilloscope or clamp-on Ammeter… well, that’s just weird. Most people use the on-board gauges to measure battery capacity, just as we did in this video.
        3. Of course the solar array was working. Now, you’re just being rude. I could tolerate the rudeness if you were correct in any of your points – but you’re not. In the future, may I suggest that you know what you’re talking about before making a fool of yourself in a public forum.

        While we’re sharing ideas, here’s one for you: Try Math.
        11,600 / 230 = 50.4
        It’s impossible – even under a cloudless sky at the equator on the summer solstice with no losses in the system – for a 230 watt solar array to charge an 11,600 Watt-hour battery in anything less than 50.4 hours.
        Our results are therefore not surprising.

        Reply
        1. Don Kane

          “on the summer solstice”

          You must mean the equinox, in spring or fall. You would need to be at the Tropic of Cancer at the summer solstice, I think, for max sun.

          And your 50.4 hours, those are 1100 to 100 hours I think. If you were using 8am to 4pm hours, would be lower, where ever you are.

          But point taken.

        2. James - Post author

          😉
          OK. Your got me. Directly overhead at the equator on the equinox. Longest day is generally around the solstice. Take your pick.
          And yeah, if you go 8am to 4pm, it’s a really long time.

    2. Don Kane

      One consideration about solar charging is when you not moving, that is, living in your house not the RV. When we are not using the RV, we want it heated in the winter (because of the water) and the refrig cold summer or winter. Regardless of how big your battery is, solar can keep up with those two tasks year round (though losing a bit Dec-Jan).

      Cheers, Don

      Reply
      1. James - Post author

        We’ve tried this, and keeping both the house and chassis battery charged while in storage is an excellent use for solar power.
        However, no amount of solar power will keep your rig above freezing at night in the dead of winter in northern climates. Because… you know… no sun at night.

        Reply
        1. Don Kane

          ” no amount of solar power will keep your rig above freezing at night in the dead of winter in northern climates”

          Right. Ha ha. Very funny.

          But the battery WILL keep the gasoline or propane heater running, at night even.

          Come on, really. Does anyone heat an RV with electricity directly?

          Still smiling, Don

        2. Don Kane

          Some day, in the not too distant future, when we all have huge batteries to power our RVs, electric heat will be normal. You are ahead of the game!!!

    3. Will

      Good video! Lithium batteries and flooded or AGM batteries are the apples and oranges of the battery world. Lithium charges much much faster and loves a higher amperage charge, while flooded/AGM batteries will take a high amp bulk charge for a couple of hours but must be finished off with a slower, lower amperage charge, of which solar is perfect for the task.

      A 1000 watt, $10.000+ lithium battery bank is a laughable expense for most, and a questionable overreach for a van. But you are right on, most solar isn’t up to the task of charging a 1000 watt battery bank, but a high amp engine alternator is perfect for the task.

      RVers should seriously look at what they need in the way of amp hours of battery storage first, then make the decision to go flooded/AGM or lithium based on their budget and lifestyle.

      Reply
      1. James - Post author

        Apples and oranges indeed.
        You’d be surprised though, at how many of our readers are actually buying lithium-powered rigs these days. Or converting their old-tech ones to lithium.
        I think the genie is out of the bottle with RV lithium, and there’s no putting him back in!

        Reply
    4. Stephen Monteith Albers

      i think electrics needs more thoughtful discussion. Your analysis, while valid, addresses only one set of operating conditions – namely routine use.
      .
      I look at solar differently. Think about pure boondocking where the vehicle sits for weeks or months, unused. This is what RVs most often do. In that case, the goal is not to run equipment, but to maintain the SOC of the battery so the owner is not faced with a dead battery when he wants to use it. To evaluate this, you need to compare the self-discharge rate of the battery to the 24/7/365 AVERAGE charge rate of the solar array. If the latter exceeds the former, then the battery will likely be fully charged when the owner needs it. And that is worth something.

      Reply
      1. James - Post author

        Keeping the battery maintained while in storage (which is what I think you’re talking about) is a good use case for solar power.
        However, even here, the use of a lithium battery changes everything.
        In the three plus years we’ve used lithium powered rigs, we’ve not noticed ANY appreciable self-discharge on these batteries. With a lithium powered coach, you turn the battery OFF for storage, and when you turn it back on – it’s right where you left it.
        However – maintaining the *chassis* battery during storage remains a concern – and we do use solar for that. We have videos on that subject.
        Keeping the Chassis Battery Charged with Solar
        An Even Better Way to Charge the RV’s Chassis Battery with Solar!

        Reply
    5. Graham Smith

      James, as was pointed out by another post the MPPT controller didn’t start charging until somewhere in the low 90% range so that impacted your study. BUT you are correct that the stock configuration isn’t going to make a big difference even with full sun. I have a 2019 Travato KL that has 215W feeding a 8700W battery and it’s not noticible. I added another 100W and on a nice sunny day that will actually gain some but only for a few hours. IF they can get the roof up into the 400W range then that could help, but you still get more charge from a quick run to the store for beer, particularly with the improved alternator on the new models.

      Reply
      1. James - Post author

        Thanks for chiming in with some additional real-world experience, Graham!
        (And we had that upgraded alternator on Parky – and it was awesome.)

        Reply
    6. Ian Furqueron

      Solar is definitely a challenge on something as small as a van/class-B. Less Junk < More Journey had a ton of panels on their Airstream trailer feeding 6 large Battle Born lithium batteries. I believe they have something similar or more on their current 5th wheel. They seem to operate reasonably well for a day or so.
      Another example is Curt and Snow on YouTube, who have a home-built Sprinter RV with a complex solar panel set-up on the roof that can angle towards the sun. Their set-up puts out over 1000 watts and seems to be the ideal set-up. Their van has a ton of neat features James might find interesting.

      Reply
    7. RoamSchooling Adventures

      Hey Guys – Thanks for sharing your experience. We also visited Big Bend last year and loved it.

      In respect to solar, its really such a complicated subject that everyone is going to have different experiences – and in turn EVERYONE is going to have an opinion on the matter.

      I designed my Kilowatt system and installed it on my 5th Wheel (we full time in ours) and I can run all my workstation PC equipment, my Fridge, TV, and fans and still charge the batteries – despite winter or summer. There’s so many factors – the most important is not just wattage, but also voltage in, MPPT vs. PWM charge controller, state of the battery and charge cycles.

      I wrote a blog and shared it on this topic if you’re interested in learning a little more – or just want something to help you fall asleep. AdFree Site – we don’t make money – we’re hobbiest just like you guys. We give away all our advice for free and donate any proceeds to St. Jude’s and East Tennessee Children’s Hospital.

      Fun video. And to your point – you’re not in a lab so its just so hard to quantify. I think you focus on what makes your experience the best it can be and just go with that. All the best out there!

      Reply
      1. James - Post author

        You’re right that solar power is a big subject. We weren’t trying to explain all the mysteries here.

        What we were trying to show – and I think we did – is that as your battery capacity grows, the contribution from solar power becomes less important. In this video we were talking, specifically, about rigs with large lithium batteries. In the months we had Parky, we never relied on solar power to charge the battery. The alternator was 60 times faster, and worked rain or shine.

        But in the end, as you’ve said, everyone needs to do what works for them. A large lithium battery might not be in everyone’s future, and that’s completely OK.

        Reply
    8. Preston Sturkie

      My wife and I both subscribe to your Youtube channel and learn and enjoy your videos. This past Saturday we purchased a new Travato 59K. Why is your comments turned off on your Youtube channel? We do not know if it is something on our end or on your end. Thank you both for making RVing so much more enjoyable.

      Reply
      1. James - Post author

        It’s not you!!

        We don’t have comments on YouTube because both Stef and I have real jobs too. This is just a hobby.
        Besides YouTube, we also maintain Facebook, Instagram, and Twitter presences, and most importantly: this web site.
        Constantly monitoring comments across multiple platforms was too much work. Something had to go.

        Every video we post has an associated article on our web site.
        You can find the link in the description, and we do encourage comments there (here). You can also ask questions on our Facebook page.
        We find that people who are willing to make the one click over are generally more likely to leave constructive comments, and the discussion is much better than the typical YouTube video.
        Cheers!

        Reply
    9. T HARRIGAN

      Ummm. I don’t have ELEVEN THOUSAND WATT HOURS!! And you pointed that out at the end of the video. I’d wager that glass of wine I owe Stef that most people out there have no where near that capacity. So I’ll continue to relish my 285 watts of solar “tea cup” pouring into my 2400 watt-hours of Lithium. 🙂

      Reply
    10. Dave

      You need to redo the test starting at say 50-75% battery at sunrise. The panels can’t charge the batteries when the batteries are full. And starting with 100% just as the sun is getting high in the sky sort of made sense that by the end of the day you used the same amount of power.

      Reply
      1. James - Post author

        Well, we don’t have that rig on loan anymore, so there’s no re-doing the test.
        But even if we could redo the test – you can’t argue against the math.
        230 watts of solar is just going to take a very long time to make a dent in a 11,600 watt-hour battery – even in ideal conditions that almost never exist.

        Reply
    11. Bobby Thompson

      Thanks for the info, it all makes sense (pretty much even for those of us mathematically illiterate.) My follow up question is long can you go with the large battery bank if you were using a/c? In my case, I would be working out of the van, sometimes for a long day. I can’t always control a projects location, and might end up in the desert during summer so I’m going to really want a/c. (Since I’m getting soft in my old age. 🙂 I’d also be running full computer set up – laptop tethered to a 32″ monitor, external hard drive, etc… (I’m a photographer/filmmaker so I need a heavy-duty edit system) Keep up the good work, I enjoy your videos. Thanks again. 🙂

      Reply
    12. Kent

      Interesting. Thank you for the comparisons and the beautiful scenery. We installed 2 100ah Li batteries in our LTV wonder which has 400w solar and find it quite adequate for our needs. Even in early February our batteries see fully charged sitting all day. Mind you we cook with propane instead of microwave and induction and rarely use AC.
      PS. As a former class A owner who had to camp outside of Chisos, we can’t wait to return with smaller rig.

      Reply
      1. James - Post author

        You’ll love Chisos!
        If what you have on your rig is working for you, we’re not about to tell you it isn’t. Keep rocking it.

        From what you’ve described, it sounds like you have almost twice the solar capacity, and only about one fifth of the battery capacity. I’d expect a different result.
        (And we’re glad you’re happy with it!)

        Reply
        1. Lauren

          I’m headed there in June! Thanks for the great video. I saw a sign in it saying “no generators” or something to that effect. Does that apply to the Travato autostart second alternator too? My van looks just like yours!

        2. James - Post author

          We didn’t ask about that. I don’t know if it would apply or not.
          (Although if it did, and you couldn’t start your engine… how would you leave?)

        3. Judy

          I’m so confused! I didnt think such a large lithium battery as yours existed, but that aside, I have a van that uses 100% solar and it rocks. No generator, no propane, 410 watts of rooftop panels and 300 watt hours from 3 lithium batteries, 3200 watt inverter. I can run my 12v AC for about 8 hours. (Plus an induction cooktop, two refrigerators, espresso machine,, hair dryer, toaster… not all at once but you get the idea.)
          I don’t know how different van setups can yield such different outcomes, but all-solar is definitely working for me. I only used shore power a few times last year when I wasnt driving and it rained for days.
          An electrical engineer designed and installed mine, and I cant take credit.
          Love your channel!

        4. James - Post author

          Well, if your van rocks your world, we’re not going to tell you it doesn’t!
          But, from what you’ve described, our systems are completely different animals. You said your solar capacity is greater (per hour) than your battery storage capacity. That’s quite a bit different from the system in Parky, where the solar panels are only 1/50th the capacity (per hour) of the battery. I’d expect different results!
          (And I’d be curious to know what kind of 12 volt air conditioner you have, if you come back.)

    13. Female Solo Traveler

      Hello my darlings, I didn’t hear you mention in the video how puny the solar panels where compared to the battery capacity, and that is a very important part that you skip around. Surely a 1000W solar array would be more fitting? I’ve met van dwellers who have that and sometimes more with way smaller batteries, and for some of them it’s the other way around: i they have enough solar panels, so the battery capacity is secondary.

      Reply
      1. James - Post author

        Well, we did say, right off the bat, in the video that using solar to charge the battery was “like filling a swimming pool with a teacup”, which pretty much sums up the relative capacities. We did speak aloud the capacities toward the end of the video. And the actual capacities of both the battery and solar panels are clearly laid out in the post above. Sorry if you somehow missed all that.

        A 1000 watt solar array simply wouldn’t fit on Parky – not without a complete redesign of the roof components. We have air conditioning, vent fans, etc. up there that we’re not willing to give up. And honestly, even a billion watts of solar panels won’t run the air conditioner or microwave all night if you don’t have enough battery capacity. Parky has other, much faster ways to charge his battery – so it simply doesn’t make sense to add that much solar.

        Reply

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