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Old 04-14-2018, 09:54 AM   #1
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Mixing Flexible and Rigid Solar Panels - Parallel vs Series

I'm about to tackle adding 2x 100W panels on my AI roof and want the installation to be as simple as possible. The existing panel is a NEW GoPower 100W FLEXIBLE panel, which was recently replaced at the end of my warranty due to delamination. I wish now I had gone with a rigid panel because I want to add rigid panels so that I get airflow underneath and avoid heat transfer into the coach. I plan to use panels and brackets from AM Solar that have VHB tape... no holes.

I would like to just use the one wire pair that already have MC4 connectors which runs down to my newly installed Victron 100|30 controller. My first thought is to wire in Series which would be around 60V at around 5.5A and the Victron would intuitively step it all down to the proper lower voltage with higher amps, right? But I hear that wiring in Series has drawbacks: if one panel is shaded it drags down the whole lot, and when the existing panel ages differently (degrades faster) it will also drag down the performance of the set.

So if I wire in parallel to avoid these drawbacks ... tell me if I got this right... can I use some of those MC4 branch connectors to first combine the two new panels mounted near the rear, then take the two new wires that now have higher amps but still at 18-20V and combine them with two more branch connectors near the existing panel? If this method works I can avoid installing a combiner box.
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Old 04-14-2018, 10:09 AM   #2
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Solar panels are a lot like batteries. Just like you can't mix size/type of batteries on a single charger, you shouldn't mix size/type of solar panels on a single charge controller. If you want to mix panels, use separate controllers and run them to the house batteries separately.
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Old 04-14-2018, 10:27 AM   #3
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Originally Posted by Protagonist View Post
Solar panels are a lot like batteries. Just like you can't mix size/type of batteries on a single charger, you shouldn't mix size/type of solar panels on a single charge controller. If you want to mix panels, use separate controllers and run them to the house batteries separately.

I think the panels have (nearly) identical specs so isn't that OK?
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Old 04-14-2018, 10:50 AM   #4
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Another plus to running the panels in series is that the higher voltage makes the mppt charger more efficient. And another negative to running the panels in parallel is the possible need to upgrade the wiring to handle the higher current. Of course, shading will likely be the determining factor in your configuration choice.

If you run the panels in series you need to match the amperage (Cmpp) of the panels. If you run them in parallel, the voltages (Vmpp) need to match. If they don’t it’s not the end of the world but your system performance may not match your expectations.
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Old 04-14-2018, 11:13 AM   #5
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Originally Posted by Tronadora View Post
I think the panels have (nearly) identical specs so isn't that OK?
As LB3 said, as long as the specs match, while not the PERFECT setup, it will certainly work mixing the two.

I would also heed his recommendation and go with a series connection, especially since we're only talking about 3 panels total. IMO the benefits outweigh any negatives. For example, if you look at the specs of your solar charge controller, you'll see that it needs to see a certain voltage at the PV input before it turns on. If you run your panels in parallel, you won't get to that voltage outside of the 4'ish hours of midday unless you live at the equator. These panels aren't very efficient off-axis with respect to the position of the sun, and since they are mounted flat and facing straight up, their voltage output suffers. By putting them in series, you're adding the voltage from each panel to reach that magic "turn on" voltage that the controller needs to see MUCH earlier/later in the day vs. what you'd get out of a parallel config, and yes, any excess above that turn on voltage will be converted to charge current by the charge controller. The net effect is you will harvest significantly more energy with the series config, all things being equal (clouds, shade, etc). Finally, if you had 3 panels in parallel, they could produce up to 18A of current. You would be right at the edge of having to replace the wiring from the panels to the charge controller. If I remember right, it's 12AWG as it comes from the factory, and you should probably be running 10AWG at that current level. You would certainly need to swap out the fuse to a 20A vs. the existing 10A that should already be there.

I hope that helps.
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