Un-matching PV panels

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Roman khan
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Un-matching PV panels

Post by Roman khan »

Hi every one.I have vmii 5kw inverter and 6 no of pv panels 4 of them are 275wp(voc 38v imp 8A) canadian solar mono and 2 are 400wp(voc 48 imp 9.8A) risen mono perc.If i connect them in series will be there any power loss due to unmatching between them?will i get the same power as matched pv panels?how much amperes will flow in wire in this condition. Will this harm my inverter?
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Re: Un-matching PV panels

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Roman khan wrote: Thu, 06 Feb 2020, 03:05 Hi every one.I have vmii 5kw inverter and 6 no of pv panels 4 of them are 275wp(voc 38v imp 8A) canadian solar mono and 2 are 400wp(voc 48 imp 9.8A) risen mono perc.

That's a severe power mismatch, but most of that is voltage. My understanding is that the 9.8A panels will produce 8A, so you'll only get 82% of current (and hence power) from them. So they effectively become 325 W panels.
What do ill this harm my inverter?
It won't harm your inverter, as long as the open circuit voltage doesn't exceed the limit. I don't know whether you might damage the smaller panels, and if so, whether there is a fire risk.

It's highly unusual practice; I would not attempt this on my roof.
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1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
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Re: Un-matching PV panels

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Linked in series the open circuit voltage would be 248vdc, depends on the inverter but if it is a PiP MS inverter the open circuit limit is 145vdc. You could connect 2 of the 38v Voc panels in series plus one of the 48v Voc panels ( 124vdc Voc) and the other 3 panels the same, then connect both strings in parallel. The MPPT controller will see the same watts and voltage from each string so it should work ok .... as long as none of the panels are shaded, then the out of balance between the two strings would cause close to total loss of that string.

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Re: Un-matching PV panels

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T1 Terry wrote: Thu, 06 Feb 2020, 12:44 if it is a PiP MS inverter the open circuit limit is 145vdc.
I was assuming a model with a 450 V or 500 V max MPPT.
You could connect 2 of the 38v Voc panels in series plus one of the 48v Voc panels ( 124vdc Voc) and the other 3 panels the same, then connect both strings in parallel.
That should just squeak it in (now assuming a 145 V max MPPT model, and temperatures very rarely below 0°C).
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.
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Re: Un-matching PV panels

Post by T1 Terry »

The real drama we are having down this way this yrs is the Vmp drop due to the panel temps. 30vdc Vmp (STC) panels are dropping to 26vdc Vmp or lower around 11am until 4pm resulting in the batteries not reaching fully charged each day. Not so bad with lithium batteries, but the lead acid batteries on the house boats and off grid houses are dropping like flies. Having to change the PWM controllers they have had since Adam was a pup and rewire the panels for an MPPT controller. Some of the panels are marked as 45vdc Voc, strange number and often I see more like 48vdc open circuit when testing them. 3 in series brings the Voc theoretically up to 144v, cutting it fine, but no problems so far.
We do see ice on the panels in winter, but never had any go more than 1v or 2v over voltage open circuit in a 3 panel series string and the inverter fires up fairly quickly and pulls the voltage low anyway.

T1 Terry
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Roman khan
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Re: Un-matching PV panels

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T1 Terry wrote: Thu, 06 Feb 2020, 12:44 Linked in series the open circuit voltage would be 248vdc, depends on the inverter but if it is a PiP MS inverter the open circuit limit is 145vdc. You could connect 2 of the 38v Voc panels in series plus one of the 48v Voc panels ( 124vdc Voc) and the other 3 panels the same, then connect both strings in parallel. The MPPT controller will see the same watts and voltage from each string so it should work ok .... as long as none of the panels are shaded, then the out of balance between the two strings would cause close to total loss of that string.

T1 Terry
My inverter vdc is 120-450v and 4000w that works without battery
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Re: Un-matching PV panels

Post by T1 Terry »

Roman khan wrote: Thu, 06 Feb 2020, 16:57
T1 Terry wrote: Thu, 06 Feb 2020, 12:44 Linked in series the open circuit voltage would be 248vdc, depends on the inverter but if it is a PiP MS inverter the open circuit limit is 145vdc. You could connect 2 of the 38v Voc panels in series plus one of the 48v Voc panels ( 124vdc Voc) and the other 3 panels the same, then connect both strings in parallel. The MPPT controller will see the same watts and voltage from each string so it should work ok .... as long as none of the panels are shaded, then the out of balance between the two strings would cause close to total loss of that string.

T1 Terry
My inverter vdc is 120-450v and 4000w that works without battery
I have as yet not worked with one of these, but I can't see why all the panels in one series string wouldn't work. You may find the larger output panels derate to that of the smaller output panels, but at such a high voltage string I have to say that I just don't know what the effect will be. You are well inside the upper limits for the MPPT controller so no problems there, just the total output is an unknown.
Please come back and let us know if the output is 70% to 80% of the total sum of all the panels, or only 70% to 80% of of 6 x 275w panels.

T1 Terry
Green but want to learn
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