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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.
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.
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!)