Cold winter temperatures can damage controllers due to low temperature effects on PV panels. Damage occurs when the cold weather panel voltage increases above the Standard Test Condition (STC) ratings.
Below is a quick, five-step worksheet to size your controller appropriately for low PV cell temperatures. You’ll need to have the manufacturer’s product specifications for the PV panels and the charge controller to complete the worksheet.
In Step #3, NEC Article 690 Table 690.7(A) Voltage Correction Factors for Crystalline and Multicrystalline Silicon Module is the source for the factor of 1.25 used to calculate a worst case panel voltage condition in -40°C weather.
There are other methods and NEC factors that might be applicable, but this is the quickest, easiest check. If you do not know about worst case ambient temperatures at the install location, then use the worst case 1.25 factor or consult the NEC.
5-Step Worksheet for Sizing Charge Controllers for Minimum PV Panel Temperatures
Step #1 Panel Voc
Enter panel Voc at STC from your panel datasheet or nameplate here:
Step #2 Series String
Enter number of the above panels wired in series here:
Step #3 Array Voc @ STC
Multiply #2 by #1:
Step #4 Array Voc with Min. Cell Temperature
Multiply #3 by 1.25:
Step #5 Controller Check
Is #4 ≥ maximum controller solar input voltage specified on the datasheet of your selected controller?
If #4 is greater or equal to maximum controller solar input voltage, the selected controller is not suitable for the system as designed. Select a controller with a max solar input voltage ≤ #4 and/or change system wiring configuration and start over.
If #4 is less than maximum controller solar input voltage on the datasheet of your selected controller, it is suitable for the system as designed.