Mismatch loss

Mismatch loss is power lost because the modules in a string do not all have the same current-voltage characteristics, so their small differences in performance cost power. Because of this, the maximum output of the whole array is always lower than the sum of each module's maximum output. A slightly weaker module limits the string current and pulls the stronger modules away from their best operating point. Very weak modules or substrings get bypassed, and all of their power is lost. Mismatch is one of the capture losses. Yield models usually apply a module mismatch factor of about 0.98. Modules can become mismatched when they degrade at different rates, so system degradation can be higher than the degradation of the modules themselves. Floating PV and bifacial modules tend to have more mismatch, partly because modules moving with the waves change tilt and azimuth within a string. Power optimisers and other module-level power electronics reduce mismatch by tracking the maximum power point of each module. In the field, mismatch can be found with string-current comparisons on combiner monitoring, or with module-level mismatch reports. In those reports, mismatch beyond plus or minus 6 percent, or a sudden increase, calls for investigation.

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• sentence 3: support check: partial - Passages say slightly lower modules limit string current, forcing lower operating point for others, and weak modules/substrings are bypassed losing all power; 'best operating point' is paraphrase, fine, but is from floating PV context only.
• sentence 4: support check: partial - Capture loss and 0.98 factor are stated, but 'yield models usually apply' is not explicitly stated; the sources show a 0.98 typical value.
• sentence 4: review: partial - IEA lists electrical mismatching as a capture loss, and two tables give 0.98 as the typical mismatch factor, but no passage says yield models usually apply it (the IEA table is of factors observed in the field). -->