A technician commissions a ground-mount array on a hot July afternoon and records each string's voltage at the open terminals before the DC disconnect closes. Every string reads several volts below the module datasheet's listed open-circuit voltage, while connections and string counts verify as built. Which factor explains the lower open-circuit voltage readings?

The correct explanation is the module temperature. Datasheet open-circuit voltage is normally specified at standard test conditions, including a cell temperature of 25 °C. In hot afternoon conditions, the cells are typically warmer, and crystalline-silicon module voltage falls as cell temperature rises; the measured string voltage can therefore be several volts below the datasheet figure even when wiring and string counts are correct. A resistive connection is a familiar cause of voltage loss in operating circuits, but an open-circuit measurement draws essentially no current, so the connection has no meaningful current-dependent voltage drop to produce this reading. Lower irradiance can also reduce open-circuit voltage, but it is not established by the scenario and does not replace the specified temperature effect as the explanation. Partial shading can reduce string voltage when it causes a bypass diode to conduct, but bypass diodes generally do not conduct during an ordinary open-circuit voltage test; shading alone is not enough to explain the result as stated. Exam caveat: module datasheet voltage is a reference-condition value, not a fixed field target, and temperature correction should use the Voc temperature coefficient rather than the Vmp coefficient. Practical check: measure module backsheet temperature and plane-of-array irradiance, then compare the measured string voltage with the temperature-adjusted expected Voc.