Double Your Solar, Double Your Fun

As the days have gotten shorter, I’ve left my rigid solar panel hooked up to the van to give it an extra boost of solar power during the limited daylight hours. I knew it would help, but I didn’t know just how much it would.

These are screenshots from the two Renogy apps that run my independent charging systems. (For whatever reason, one came with a BT-1 Bluetooth adapter and the other came with a BT-2, which means I need two different apps to display their info.) The one on the left is a readout from my solar charge controller, which handles power from the 350 watts of solar panels permanently mounted to my roof. The one on the right is from my DC-DC charger, which provides power from the alternator when the engine is running and is now where I plug in my 200-watt rigid solar panel for an extra boost while stationary.

By a strange coincidence, both independent systems are each pumping 150 watts of power into my batteries in this example. Even stranger is that they’re charging the same amount quite consistently. I’ve double and triple-checked that the data is correct, but since the Bluetooth interfaces are hardwired into their respective devices, there’s no way they can be getting each other’s data. They’re genuinely charging the same amount, meaning that the additional panel is truly doubling my charging capability.

The strangest part is that a single 200-watt rigid panel is generating the same power as my pair of 175-watt flexible panels on the roof of the van. The last time I checked, 200 does not equal 350. I can think of a few reasons why this is happening:

  • The rigid panel is brand new. I bought the flexible panels new as well, but they’ve been sitting on top of my van for over a year and a half, so maybe they’ve lost some of their effectiveness.
  • Rigid panels may be more efficient than flexible panels. It’s possible that flexible panels give up a little bit of charging capability to be able to bend the way they do.
  • A little tilt goes a long way. While my flexible panels are stuck to my roof, pointing straight up and taking whatever power they can from whatever angle the sun is at, my rigid panel sits at about a 30º angle. I also rotate it a couple of times throughout the day to keep it pointed toward the sun. Particularly since the sun is at such a low angle in the sky this time of year, even at noon, I think the angle is probably having more effect than anything on the panel’s efficiency. Solar panels are most efficient when they’re aimed directly at the sun. I can’t aim my rooftop panels this way. So even though my rigid panel is only rated for 200 watts, it’s putting out much more of its potential power simply because I’m aiming it toward the sun.

I should keep this in mind for my next rig. I see plenty of RVs, buses, etc. here in Quartzsite that have their rooftop solar panels mounted on racks where they can tilt them up, like I’m doing with my external panel, to catch more of the sun’s rays when it’s low in the sky. But then, if I do a setup like Arin did on her bus, with a pair of cheap 250-watt 24-volt panels (and use a charge controller that will handle that kind of voltage), I may not need to aim anything at all. For the price of these used panels, I might as well just throw more solar panels at the problem.

It’s not an option for my current van, but my external panel solution is working wonderfully. At this rate, I may not even need to run my generator this winter, even though this situation is precisely why I got it in the first place.

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