The temperature correction factor depends on how the modules are mounted and is needed to calculate the module temperature and string voltage correctly.
The temperature correction factor states how much hotter the PV modules get than the ambient air. It depends on how the modules are mounted: the less ventilation behind the modules, the hotter they get.
autarc needs the factor in string planning to derive the real module temperature, and with it the string voltage, from the ambient temperature.
Why does it matter?
A solar module's voltage rises in the cold and drops in the heat. To calculate the minimum and maximum string voltage correctly, autarc needs to know the real module temperature.
In winter: cold modules = higher voltage → risk of overvoltage at the inverter.
In summer: hot modules = lower voltage → risk of the voltage dropping below the inverter's MPP range.
How does autarc use the factor?
autarc calculates the strings for two extreme cases:
Hottest case: autarc adds the temperature correction factor to the maximum ambient temperature. This gives the minimum string voltage and the maximum current.
Coldest case: autarc uses the minimum ambient temperature without a surcharge, because without sunlight the modules are roughly at air temperature. This gives the maximum open-circuit voltage.
Module temperature (hot) = max. ambient temperature + temperature correction factor
Module temperature (cold) = min. ambient temperature
Example: with a maximum ambient temperature of 35 °C and flush-mounted modules on a sloped roof (+35 °C), autarc calculates with a module temperature of 70 °C.
Module temperature (hot) = 35 °C + 35 °C = 70 °C
Setting the temperature correction factor
In the PV planning, select the inverter.
Under
Ambient temperature, enter the values forMin. (°C)andMax. (°C).Next to
Ambient temperature, click the surcharge (+35°by default) and select the mounting type.
Typical surcharges by mounting type
Mounting type | Temperature correction factor |
| +35 °C |
| +30 °C |
| +25 °C |
| +20 °C |