# Loss Factor Calculations

Loss factors are computed on a Block by Block basis. A final weighted average is also provided where applicable. The reference points for each of set loss factors quotients are shown in small caps text.

### Figure 43. Loss Factor Definitions

The non-STC losses (loss due to lower efficiency at lower irradiance levels, and the loss due to the module temperature coefficient), are detailed as follows:

**Module Irradiance Loss**

**Reference**: Compute the array *P*_{mp} at STC conditions (1000 W/m^{2}, 25 °C, air mass 1.5, incidence angle of 90 degrees) and scaled to the effective irradiance. Let this be denoted by *P*_{mp,ηSTC}: E.g., @ 200 W/m^{2}, energy output shall be defined as 1/5 the energy at STC. In other words, we assume a linear irradiance dependency of module power.

**Irradiance Loss**: Compute the *P*_{mp} under actual irradiance conditions but with module temperature fixed at 25 °C. The difference between this P_{mp} and the previous P_{mp} will be the energy lost (or gained) due to the module’s response at different radiant intensities.

**Module Temperature Loss**

**Temperature loss**: Compute the *P*_{mp} under real conditions (actual temperature and irradiance). The difference between this P_{mp} and the previous P_{mp} will be the energy lost (or gained) due to the modules temperature response; i.e. operation at temperatures other than 25 °C