As the name suggests, this is the minimum temperature extracted from the meteorological data set (TMY) selected by the user. This value is used to size the number of modules per string, which has electrical and civil implications.
If you click on "Show details" (Design Process > Location > Meteo data), you can see other values for minimum temperature above certain values of irradiance. Statistically, minimum temperature happens during the early hours of the morning. However, if your inverters operate only above a certain irradiance threshold, for example, 10 W/m2, you could choose to disregard all temperature values that happen when the irradiance is below 10 W/m2. To do so, simply copy-paste the value from the “Show details” section into the minimum historical temperature input.