Panels with different Voltage - Problem?

[timmbo]

Hi all PV-Friends.

I got right now 3 different PV-Panels.

1x 23V Voc 90 Watts
1x 23V Voc 100 Watts
1x 23V Voc 130 Watts

Those 3 are in parallel Mode, so its no Problem.

I saw today a PV-Panel with 41V Voc 325 Watts for a good price.

Jinko Solar JKM325M-60 Cheetah 60M

Jinko Solar JKM325M-60 Cheetah 60M - monokristallines Hochleistungsmodul mit 325 Watt in 5 Busbar-Technologie Nennleistung (Wp): 325 Kurzschlussstrom (A): 10,20 Nennspannung (V): 33,6 Nennstrom (A): 9,68 Leerlaufspannung :...

www.photovoltaik4all.de

So, what matters if i set the 41V Modul in parallel mode to the other?

The point is, that with a higher Voltage my VE MPPT 100|30 gets more power and earlier and longer.

Bye
Timm

 

[offgriddle]

That's a really REALLY good question! Would the 41 volt panel average out amongst the other three 23 volt panels in parallel to create an agggregate voltage somewhere between 23 and 41 voltas? What if the 23 volt panels are not capable of having 41 volts on their outputs would they be damaged? Help!

 

[gnubie]

Under light loads the higher voltage panel would carry the load, as the load ramps up it will be pulled down to the point where the other panels are.

The higher voltage panel would push current into the lower voltage panels until that point is reached. The output of the higher voltage panel would be shared amongst the load proper and the other panels. Given that there are 3 other panels, and combined with their rating, I wouldn't expect any damage to occur if there was no load proper, just panels. The fact that the 3 other panels are actually trying to push electrons means they present a higher impedance to the high voltage panel also reduces the chance of damage.

This is partially from practical experience. I had a non-fused set of 4 2nd hand Trina panels on test in parallel. One panel had a cell fail open circuit significantly dropping the voltage the panel could produce and the other panels in the set pushed approx 4 amps at 30 (?) volts into it. Fortunately hot plastic smell alerted me to the problem before anything caught fire.

As always when there are more than 2 panels / arrays in parallel fuses should be in line with the sets to protect against shorts etc in the panels and them actually drawing significant power from the other panels and melting / catching fire.

 

[timmbo]

Hi,
Thanks for the detailed information.
What would matter if the 2 Panels with about 100Wp i set in serie and the 41 in parallel mode to them?
So one array has 46V and the other 41V.

The Voltage difference is not high, so maybe it wold work.



Thanks
Timm

 

[gnubie]

It'd be happier overall but you will have compromises. The MPPT controller will sweep the current up and down so at some point in that sweep it will pull the voltage of the 2x string down to where the lower voltage panel is and it will notice the change in current as the panel starts to provide power but that may not be the MPP so the controller may well let the voltage rise back up effectively cutting the 41v panel off again. Either way one of the strings will be running off its MPP so will be under-producing.

It's a going to be a complex interaction depending on sun exposure on each string.

You might think about buying a diode to put in line with the 41v panel to completely prevent current flowing into it since you are trying to get as much power out of the setup as you can. The diode might dissipate around 5 watts if the panel is ever called on to deliver its full ability.