On Sunny Portal installations with two or more inverters, the platform compares the output of the inverters with each other. If there are significant differences in output between them, Sunny Portal may issue an error message with the text ‘performance deviation’. The message will also indicate how much (%) the specific inverter deviates from the others—or from the average, if there are more than two.

By default, Sunny Portal is set to trigger this error message only when a deviation of 20% or more is detected. This is to avoid unnecessary alerts caused by normal, minor variations. However, this setting can be adjusted—for example, when two inverters are connected to systems with very different tilt angles and orientations. If you have one inverter connected to panels on an east-facing roof and another on a west-facing roof, their yield could easily differ by more than 20%. On a sunny morning and a rainy afternoon, this setup could trigger a deviation message.

To change the 20% setting, go to Sunny Portal and click on ‘Configuration’ and then ‘Device Overview’. Click ‘Properties’ for each inverter.

Then scroll down to ‘Inverter comparison’ and click ‘Edit’:

Here you can change the 20% deviation threshold:

Note: The deviation is calculated based on specific yield, in kWh/kWp. This allows for a fair comparison even between inverters with different power capacities. For accurate comparison, it is important that the correct peak power (in kWp) assigned to each inverter is entered.

P.S. A communication issue can also trigger a performance deviation! If one inverter is not transmitting data to the Portal while the other is, Sunny Portal might interpret that as a 100% deviation. In many of these cases, the problem is simply a communication error. Check the page Online monitoring has stopped, now what? for troubleshooting tips.