It is common for panels on the same roof to vary in energy generation. Many factors can cause these variations, such as panel direction, shading from chimneys or trees, and other obstructions.
Solar panels are “mismatched” directly from the factory and can vary. This is normal.
The solar panels that are being compared may not be on the same roof. In this case, they won’t receive the same amount of sun each day.
One of the panels may be obstructed or shaded for a part of the day. For example, a neighbor’s roof may shade lower panels for part of a day, or one panel may have the shadow from a vent stack come across it each day.
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