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Old 04-19-2015, 12:02 PM   #1
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Solar panels with varying voltage; 18v vs 22v

I've got a panel I use with a MPPT controller a lot; it's a 100W panel that has an open circuit voltage of 22v. Works great. I'm probably gonna have an additional panel; it's not in my hands now but the specs I found online seem to indicated an open circuit voltage of 16-18v; it's a 24W panel.

My question is how to wire this so I can temporarily connect this to my existing solar. Currently (heh) I use my 100W via an external cable to the controller; it's not mounted permanently so I can move it into the sun when the van is in shade. Can I just add the new lower voltage panel in parallel?

thanks,
Rob
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Old 04-19-2015, 01:27 PM   #2
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Re: Solar panels with varying voltage; 18v vs 22v

I'm no expert, but from what I have read if you connect two panels of varying voltages in parallel, then both panels will be "dragged down to" the lowest voltage of the two. So, you'd be giving up power from your higher-voltage panel. Seems that the recommended variance is something less than .5 volts, just to give an idea of what I have read.
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Old 04-20-2015, 05:23 PM   #3
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Re: Solar panels with varying voltage; 18v vs 22v

Yeah, that rather makes sense. But does it depend on the controller?If you wire both into the controller itself? I would probably not need to use both together, but it might be handy.

Could I avoid the problem if I connect each panel to its own controller and then to the 12v system? I realize that may create some battery sensing issues for charging, but I'm wondering if it would be useful while running loads during the day. Thinking about it, the extra 1-1.5 amps probably wouldn't charge my batteries any faster than the 100W panel which can do over 3A (and probably more).
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Old 04-20-2015, 06:16 PM   #4
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Re: Solar panels with varying voltage; 18v vs 22v

With your MPPT controller you could wire them in series, as long as you keep them both out of the shade you should be good. You could go with a separate controller, but that could bring other issues,

-greg
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