This surprises solar customers every summer: solar panels produce LESS power when they’re hot. The temperature coefficient of power for most silicon PV panels is around -0.35% to -0.45% per degree Celsius above 25 degrees C (the STC rating temperature). A panel rated at 400W at 25 degrees C will produce roughly 360-370W when the panel temperature hits 60 degrees C on a hot summer day - about 8-10% reduction.
Panel temperature is not the same as ambient temperature. A panel in full sun on a hot day can reach 60-80 degrees C even when the air is 35 degrees C. The mounting matters - rack-mounted panels with airflow underneath stay cooler than direct-mounted panels on a tile roof with no air gap.
For the electrician, why this matters: string voltage is also temperature-dependent. Panel open-circuit voltage (Voc) INCREASES as temperature decreases. Cold winter mornings can push string voltages higher than you’d calculate from the datasheet at 25 degrees C. You need to calculate maximum string voltage at the minimum expected temperature. The inverter’s maximum input voltage must not be exceeded under any conditions. Get this wrong and you’ll fry the inverter on a cold morning.