String

Because the modules are in series, the whole string carries the same current, so the weakest module sets the pace: partial shade, soiling or a mismatched panel on one module drags down the entire string. That is the core argument for module-level electronics such as power optimisers and microinverters. String length is bounded at the top by Voc in cold conditions and at the bottom by the inverter's minimum MPPT voltage on hot days, and the usable window between those two limits is narrower than it first appears. Keep all modules in a string identical in model, orientation and tilt.