System Underproduction and Overproduction Issues

If the system appears to be underproducing or overproducing, there are several potential causes.

 The first step of the troubleshooting process is to gather information from the technician on-site and from SolisCloud.

1. PV module brand and model number OR photo of the PV module spec label

2. String details for each inverter in the system: 

     a. Number of PV modules per string

     b. Orientation/azimuth of each PV array/string in degrees or bare minimum west/east/south/south-east etc.

3. Address of the site so that we can look it up on Google satellite image

4. Are there any obstructions such as trees, chimneys, vents, etc?

5. What is the weather currently at the site?

6. PV string voltage and current measurements on site and on SolisCloud - these should be relatively close to each other

7. Use the module and string details to determine what the string voltages and current should be, compare with what the actual string measurements are.

Example 1:

• x30 modules 400W, two strings of x15 modules going to one inverter S6-EH1P11.4K-H-US. Nameplate rating of the PV system would be 30 x 400 = 12kW
• Both strings are in the same array facing 270 degrees west
• Module Vmp = 30.3V and Imp = 10.26A
• When inverter is in operation, string 1 voltage shows as 495V and string 2 shows as 485V
• When inverter is in operation, string 1 current shows as 7.6A and string 2 shows as 7.9A
• Total inverter AC output power shows as 7.34kW, which may be seen as underproducing by the homeowner who expects to see 11.4kW
• What is the issue here? Is this system actually underproducing?
• Hint: The system will never ever produce 12kW even in the most optimal conditions with a 180 degree pure south-facing array.
• Answer: This system is NOT underproducing. The reason for the appearance of underproduction is due to the fact that the array is facing west. If the time is before noon then that is definitely why there is underperformance. 

Example 2:

• x26 modules 445W, two strings of x13 modules going to one inverter S6-EH1P11.4K-H-US. Nameplate rating of the PV system would be 26 x 445 = 11.57kW
• Both strings are in the same array facing 165 degrees southwest
• Module Vmp = 34.8V and Imp = 12.79A
• When inverter is in operation, string 1 voltage shows as 465V and string 2 shows as 460V
• When inverter is in operation, string 1 current shows as 10.5A and string 2 shows as 10.2A
• Total inverter AC output power shows as 9.3kW, which may be seen as underproducing by the homeowner who expects to see 11.4kW
• What is the issue here? Is this system actually underproducing?
• Hint: The system will never ever produce 11.57kW even in the most optimal conditions with a 180 degree pure south-facing array.
• Answer: This system is NOT underproducing. The reason for the appearance of underproduction could be (1) hot PV modules causing derating (2) time of the day, since this is a south-east facing array if the time is late afternoon then we should expect lower production.