voc cold weather adjustment

[mtmtntop]

I am learning about matching components and understand that i need to verify that the voc for the array will not exceed the maximum pv array power spec of the inverter. I live in montana and -30c is not unheard of, and it hit -40 (either c or f) last winter. I planned on using 20 Canadian solar cs 6r 400 ms-hl panels and the still to be released sma sunny boy sbse4.8 inverter because i want the emergency circuit available if the grid goes down (no battery backup planned) the voc for these anels is 36.8 volts. when i calculate the conversion factor at 40 below its 43v per panel. and 43 x 20 panels is 860 volts, far above the inverter limit of 600. do i have to reduce the number of panels to fit this scenario to 12 panels to stay below the 600 volt limit? And 2 other related questions. i thought you could assume 80 to 85 % efficiency of the array in total but don't see that factor brought up anywhere when calculating the cold weather factor. and 2, i also thought that an inverter would "clip" the additional voltage and it would just be produced but unused power. thanks for your help

 

[green mountain boys]

You have to calculate for the coldest possible temperature.
You need to be below 600 volts.
Clipping does not apply to voltage calculation.
The 80 to 85% efficiency you are referring to does not apply to this calculation.

 

[sumpower]

NEC table 690.7(A) gives a correction factor of 1.25 at -40F
So a Voc of 36.8 x 1.25 = 46 Volts @ -40F

Panel efficiency of 80 to 85%? Cloud effect or cloud lensing can cause the intensity of the light to increase temporarily. Thus increase the output of the panels to 100%. Cloud lensing is caused by ice particles redirecting the light. At times I get 100% of the panel wattage output due to this.

Charge Controllers clip amperage as solar panels are considered a current source, at MPPT voltages and lower. Voltage is not clipped.