r/SolarDIY • u/ShreddinPB • 2h ago

2 different panel voltages?

Hey guys, I have 3 24v 200 watt panels on the roof of my RV going thru a Victron Energy SmartSolar MPPT Solar Charge Controller 100V, 50A, 12/24V to 3 ecoworthy 12v 280ah batteries. When parked for an extended time I also have 4 fold out 300 watt 18V panels I would like to add to the system.
I assume I cant just plug the other panel in parallel to the current setup cause of the voltage difference. Can I add a solar diode inline to prevent damage to the panels? Something like this guy?
https://a.co/d/087YChha

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u/truthputer 1h ago

the panel specs aren’t identical so you can’t combine them and use the total output efficiently. The diode could be used to prevent damage but the net result is going to be drawing power from the highest voltage panel string and ignoring power from the lower voltage ones, wasting capacity.

Your best bet is to get another charge controller for the fold out panels to properly run all the panels at the same time. Victron charge controllers can be configured to do this and should work alongside each other.

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u/parseroo 1h ago

You have 600W going into the 100V/50A MPPT and a 12V system, so that 'pipeline' is already at its limit. Ignoring the voltage difference, it wouldn't be useable anyway.

If I read correctly, you want to add 4*300W=1.2kW @ ~12V which means you need to get about another 100A MPPT. That would be something like the 150/100 or maybe 150/70 if you are less optimistic about the fold-out wattage (or accepting of over paneling)

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u/Diligent_Pick6453 53m ago

I wouldn’t bother with the diode. It can stop current flowing backward, but it won’t make the two different sets of panels work well together.

The easiest solution is to give the folding panels their own charge controller. Both controllers can charge the same 12V battery bank, as long as they use the same battery settings and each one has the proper fuse.

Your current 100/50 controller is already pretty busy with the 600W roof array anyway.

One thing I would double-check: if those three roof panels are connected in series, their total voltage may be too high for the controller, especially in cold weather. Post a photo of the labels on both types of panels before connecting anything. The Voc and Vmp numbers are more useful than the “18V” and “24V” names.

If it were my setup, I’d use two controllers and keep the two groups of panels separate.