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hookem avatar image

Yet another Series-Parallel question: 6 * 100W panels on Sprinter RV

Seeking advice on optimal setup (6 * 100W on RV roof-top, taking shade into account)
Here are the specs on the 100W panels:
Voc = 25.4V, Vmp = 20.5V
Isc = 5.23A, Imp = 4.95A

Here are the options I'm considering so far:
1) 1 MPTT 100/50 Controller: 6 panels in Parallel.
2) 1 MPTT 100/50 Controller: 3 Sets of 2 Panels in Series, with the 3 Sets connected in Parallel
3) 1 MPTT 100/50 Controller: 2 Sets of 3 Panels in Series, with the 2 Sets connected in Parallel
4) 2 MPTT 100/30 Controllers: 2 Sets of 3 Panels in Parallel per controller
5) 2 MPTT 100/30 Controllers: 2 Sets of 3 Panels in Series per controller
6) 3 MPTT 100/20 Controllers: 3 Sets of 2 Panels in Parallel per controller
7) 3 MPTT 100/20 Controllers: 3 Sets of 2 Panels in Series per controller

Thanks in advance for your feedback.

mppt smart solar
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2 Answers
gro avatar image
gro answered ·

To get the best low light performance having panels in series will generate the voltage necessary to wake up the controller. Least problems from shading will be obtained from a parallel configuration. For me it would be either option 5 or 7. Option 7 gives you best performance in shade from those two and also the best graceful degradation should a controller or panel go down.

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Kevin Windrem avatar image
Kevin Windrem answered ·

I had similar questions when I installed 4 100 watt panels on my RV. I ended up doing a bunch of tests including partial shading in both all parallel and all series configuration. For my system, all series had a slight edge with partial shading. It is amazing how little shade it takes to shut down a panel. And pretty much any shade cuts the output in half. The panels I have run two strings of cells in parallel so that probably explains the 1/2 output with any shade.

You will always be better off with more controllers. In any situation where a panel has reduced output and is combined with other panels before the controller, the array's output will be limited by the compromised panel. In a series configuration, the string's current will be limited to the compromised panel. In a parallel configuration a compromised panel probably has a reduced max power voltage so it's contribution essentially drops to zero.

If you have the money, I'd go for 2 panels to a controller. After installation, run tests to determine if you are better off with series or parallel.

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