Just as human beings can find it harder to get to grips with their activities on a hot day, the efficiency of many electrical assets changes with the ambient temperature.
When the temperature rises in the summer, people often say that solar power must be working at full strength. In fact the opposite is true. For PV it is light – not heat – that is the source of power, so PV panels are at their most efficient when the ambient temperature is low. So a cool day with many hours of sunlight striking at the most beneficial angle works best.
Large arrays are at risk of overheating on a hot day.
How much efficiency is lost? It’s not a huge effect – typically PV panels lose about half a percentage point of efficiency for each degree of ambient heat rise. Standard information from the manufacturer will give the PV panel output at 25°C and the ‘power temperature coefficient’, which describes how that figure changes with temperature. Equally, efficiency improves on the nameplate rating as the temperature drops below 25°C.
The effect is not restricted to the PV panels, efficiency is also lost in the inverters. Researchers found that inverter efficiency falls by about 2.5% when the ambient temperature approaches 40°C.