A controller / panel question to verify, please?

ILFE · January 2014

I just read something on a website basically stating, "MPPT controllers have an advantage over PWM controllers and panels in series have an advantage over panels in parallel, in that they will produce more power on cloudy / rainy days."

Is this true? If so, can you explain why? I realize that MPPT controllers make your system more efficient and make better use of the power generated by the panels. But, is there more to it than that?

vtmaps · January 2014

Re: A controller / panel question to verify, please?

ILFE wrote: »

panels in series have an advantage over panels in parallel, in that they will produce more power on cloudy / rainy days."

Is this true? If so, can you explain why?

I don't think its true.

BUT... when there is PARTIAL shading all bets are off. And that is a very complicated thing to analyze. It depends on the partial shading (is one string partially shaded or is one panel in a string partially shaded). And it depends on the specs of the panel and the internal construction of the panels (bypass diodes, number of strings of solar cells within the panel). And it depends on the controller (PWM or MPPT).

And it depends on whether you are using DC optimizers on each panel (or microinverters, for grid-tie systems). And it depends on whether we are discussing amorphous or crystalline panels. And I'm sure I must be leaving something out.

--vtMaps

ILFE · January 2014

Re: A controller / panel question to verify, please?

vtmaps wrote: »

I don't think its true.

I didn't think so either. All things being equal - panels having identical specifications in both cases, and just using an MPPT as apposed to a PWM controller, I believe the only difference would be the typical efficiency of MPPT over PWM. I cannot see where panels in series would have any advantage over panels in parallel.

Oh, no shading would be involved here. We are talking ONLY rainy / cloudy skies above.

westbranch · January 2014

Re: A controller / panel question to verify, please?

the only time I can think that there MIGHT be more more output seen is if it is a 12 v system and the parallel panels are producing tenths of an amp, ie not able to feed enough, barely, the MPPT CC. In this case/setup the panels in series , say at 24 v , might show some output and charge the 12 v battery. And how many times would you be in that situation? maybe once a day at sunrise?

Cariboocoot · January 2014

Re: A controller / panel question to verify, please?

No, not true. Panels are a current source. Add cloud cover and the current drops for all the panels, whether in series or parallel. The fact that the Voltage is higher with a series connection does not mean more power is available, only that the power comes at a different I*V point.

MPPT controllers offer a small power advantage under 'normal' conditions in that any Voltage difference between battery level and Vmp of an array may be turned into extra charging current if it is not lost in the resistance of the wiring.

Under "shading" conditions it is as vtMaps says: all bets are off because "shading" is a vague term that covers everything from light to heavy cover afflicting anywhere from one cell to the whole array.

A controller / panel question to verify, please?

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