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Do I have to consider anything on the amps when mixing panels in series?
The 256W have Ampp 9.33A and 285W are at 9.1A. Does this mean that maximum current through the string will be 9.1A? It would be no problem, but good to know how it works in this situation.
As I see it now, the setup will give:
9.1A at 86.36V for string one
9.1A at 90.13V for string two
Then the Classic will find a midpoint between the two?
Hi Englebretsen,
The primary thing to consider in mixing PVs in series is the Imp of each. Having all Monos, or all multicrystals in each string may help, may not. Certainly, mounting strings of PVs with different mounting dimensions could be a bit of a hassle.
Yes, in series strings of different PVs, the STC Imp of the string will be about that of the PV with the lowest Imp. As you know, we seldom see STC outputs, without reflections, or perhaps with very cold weather. Often at Solar Max, we see about 75% of STC power ratings.
As I see it, string one will be two two 285 W PVs, and one 256. This would give a calculated STC string Vmp of about 31.3V X 2 = 62.6V plus 27.5V for the 256, which equals about 90.1 V for that string.
Three 285s would give STC string V of about 93.9V.
Am simply summing the STC Vmps of each PV in the string to get the string V. When using strings of PVs with different STC Vmps, one would expect that the Pv with higher Isc might well have a bit higher Vmp at STC conditions, due to it being loaded a bit less, causing its Vmp to rise a bit (IMO).
Since there are variations between PVs with identical specs, and the output of the PVs vary considerably due to variations in Irradiance and temperature, clouds, haze, and humidity (etc), have not spent too much time trying to calculate what will be the power output, assuming certain conditions, but that is just me ...
The above calcs may have some flaws, but this is the way that we look at it.
The Classic should find a MPP that is between the Vmps of each of the two candidate PVs, for the Irradiance and cell temperatures at that moment.
Hope that the above makes some sense. Vic