Connecting different sized Victron Energy PV modules: Series or Parallel?

Most Victron Energy technical questions are answered by Victron Energy dealers or by contacting Victron Energy customer service on +31(0)36 5359703 or emailing them at  service@victronenergy.com. Others get answered here on the blog and on Victron Live, using the Disqus comments section.

Sometimes the sales team receive them directly too. Here is one question received by Bob Hopman about whether you can place different sized Victron Energy PV modules together and whether series or parallel is best. I found this one interesting, hence a short blog.

John Rushworth

Question by an Australian customer

Subject: Victron MPPT question

Bob,

I hope you don’t mind a silly question. I have a Victron MPPT 75/15. On the roof of my camper van is a 100 Watt solar panel, which is wired into the MPPT.

That’s all great, however sometimes at camp, I’d like to also wire in a completely separate solar panel (a ground standing one) directly into the MPPT but not in parallel – just 2 sets of DC leads from the respective panels to the MPPT.

Is this possible or OK to do?

Its an otherwise simple system

Thanks.

Brad.

Answer by Bob Hopman

Subject: Re: Victron MPPT question

Dear Brad,

This isn’t a silly question.

There are a couple of things to keep in mind!

Placing different modules in series is possible as long as the open circuit voltage (Voc) does not reach the maximum of the MPPT at cold temperatures.

A few things to note first. Our MPPT Calculator excel sheet does not allow different types of modules in series, so be careful with that. Please also note that damaging the MPPT by applying too high a voltage invalidates the warranty.

There are advantages/ disadvantages for placing them in series or in parallel. Please look at the following image, where I took 2 imaginary PV modules and placed them in series and in parallel:

Series Parallel

You can see, in this case it would make more sense to place them in series, because the voltages are added and the lowest current of both modules will define the maximum current of the system.

While placing them in parallel you can see a different story, currents are added and the lowest voltage will determine the ‘PV system’ voltage => which in this example results in a lower output power.

If the current would exceed the maximum of 15A, this would not damage the Victron MPPT. To understand this unique feature see my blog: Matching solar modules to MPPT charge controllers

Of course if you combine two different modules in a system, it will be more difficult for the MPPT to find the optimum maximum power point, but it would work!

So it really depends on the modules which you would like to combine in the system – although my best advice is to always keep the system robust and use the same size/wattage of Victron Energy PV modules.

Safety note: I’d never advise to do this in a working ‘live’ system. Always correctly disconnect the battery and panels (and if applicable loads) before changing anything.

I hope this answered your question.

Good luck with your PV system!

Kind regards,

Bob Hopman
Sales Manager
Victron Energy B.V

Victron Energy 40 Years - 1975 -2015

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