Reflection in module plane

The radiation on the inclined PV generator plane is reflected on the module surface and leads to radiation losses. The direct radiation component is reflected depending on the position of the sun and the angle correction factor of the module.

For the reflection losses, the incidence angle modifier ($IAM_{50}$) is specified in the module data, which indicates how high the reflection is at an angle of incidence of 50°. The reflection for any angle of incidence can then be calculated from this factor according to the ASHRAE model (originally from Souka and Safwat).:

$b_0 = \big( 1 - IAM_{50} \big) \big/ \big( \frac{1}{ \cos { 50° } } -1 \big) $

$E_{\text{reflection loss, }\theta_{\text{gen}}} = b_0 \big( \frac{1}{ \cos { \theta_{\text{gen}} } } -1 \big) $

With increasing, i.e. flatter angle of incidence, the reflection losses at the module surface also increase.

Reflection losses for different values of $IAM_{50}$ and $b_0$ respectively.


Souka, A. F., & Safwat, H. H. (1966). Determination of the optimum orientations for the double-exposure, flat-plate collector and its reflectors. Solar Energy, 10(4), 170–174.

See also