Soiling loss index details

In terms of quantities that can be measured directly from a PV panel, soiling loss index (SLI) is defined as the loss in the irradiance reaching the solar cells of a PV panel. If all other factors are the same, this loss is primarily due to the loss in transmission properties of the glass as a result of soiling.

Irradiance (W/m2) is calculated from short-circuit current as:

Eq. 1

Where:

  • Geff= effective irradiance reaching the solar cells (W/m2)

  • ISC,STC = short-circuit current at standard test conditions (STC)

  • T = back-of-panel temperature (°C)

  • T0 =back-of-panel temperature at STC, typically 25 °C

  • α = temperature coefficient of short-circuit current

SLI uses the effective irradiances of a clean reference panel and a dirty test panel. It is defined as:

Eq. 2

Where Geff,Ref is the effective irradiance calculated from the clean reference panel, and Geff,Test is the effective irradiance calculated from the test panel.