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kaplan78 avatar image
kaplan78 asked

Fixed roof panels AND portable panel???

Hello, I'm putting some fixed panels on my van roof, but also want to wire in a quick disconnect so I can add a portable panel. Often I like to camp in shade which renders the roof panels worthless. I wanted to be able to plug in a portable panel to set out in the sun and use the same controller (Victron 100/30). The roof panels would be wired in parallel so I don't see anything wrong as long as my wire is rated properly and I don't exceed the load of the controller, which my 280Watts total would not do. Thanks for any feedback!


MPPT Controllers
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4 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

With roof and ground arrays in parallel, you might see a conflict in partial shading situations. A higher voltage could eclipse the array that has good sun. If array voltages are similar, you will probably be OK. But you may consider two breakers, one for each array so you can shut down the one you aren't using.

Another configuration is with all panels in series. You need to insure the MPPT's maximum input voltage isn't exceeded even at the coldest temperatures to avoid damage. You'd also need a way to bypass the ground array when not using it, e.g., a switch.

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kaplan78 avatar image kaplan78 commented ·

Great thanks Kevin great information. I appreciate the advice here and it seems to be the smart way to go about it. I'm all about overkill when it comes to electrical safety. I was hoping the roof and ground could both run in perfect harmony.

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Kevin Windrem avatar image Kevin Windrem kaplan78 commented ·

I think the best way to insure the arrays would be to put them on separate charge controllers, but a series connection is workable also.

Panels need bypass diodes to function in series but most panels do. To find out, wire the panels in series and put one in the sun and cover the other one. If you get power, the diodes are in place. If not, they can be added externally.

Panels wired in parallel need isolation diodes to prevent back feeding voltage from one into the other. lanacorp discusses this. Many panels have internal isolation diodes also.

In both cases, the diode you want is called a Schotky diode. You can buy these in MC4 connectors, or as raw diodes and do your own wiring. The diodes need to be capable of the open circuit voltage of the panel or array they are across or in series with, and the short circuit current of the panel/array. A 1N5822 is good for 3 amps and 40 volts and suitable for individual 100 watt panels.

The panels need to match in voltage output if they are to be paralleled. Panels need to match current if placed in series.

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launacorp avatar image
launacorp answered ·

Just look in the Servicebox behind the panel. There u will find some diodes. Buy 2 of these (on eBay or so) and then make a parallel connection as u planed.


When one array is in sun and the other is in shadow side, the one in the sun doesn't heat the one in the shadow an all things are good. Make some switches or breakers if u want to disconnect the one or the other.

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sprinter2072 avatar image
sprinter2072 answered ·

I bought a second Victron MPPT the 15 amp one - they aren't very expensive. I wired in a switch to connect the extra panels to my yeti box (which has its own controller) for charging or switch back to the Victron MPPT. These are smaller panels than the ones on the roof so I didn't want to wire in series or parallel with my main panels. If you mix panel sizes you'll just have problems - you'll either limit voltage or limit current.

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Nickus de Vos avatar image
Nickus de Vos answered ·

KISS (keep it simple, stupid)

2 pares of cables connected in parallel on your MPPT controller, the one pare running to your roof panels, the other pare running to a connector placed somewhere on your van where you can connect the portable panel when parked.

Put a switch or even a circuit breaker in-line on each of the 2 cable pares, if you use the portable then switch off the roof and vise versa.


If the roof panel and portable panel is the same voltage, then it will even work just like that, without any switches. Shading isn't a problem in parallel systems, it can however become a problem in series systems.


Remember to stay within the VOC rating of your MPPT controller and be sure the switches or circuit breakers you choose can handle the voltages and current involved.

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