Soiling loss factor

What this step does

The row measures the light that dirt and snow on the module glass take from the plane irradiance. Each month's soiling fraction removes that share of the plane irradiance after the shading rows. The row appears even when every month is zero, so the diagram keeps its shape.

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000}\sum_i L_i \tag{1}$$ $$L_i = s_{m(i)}\,G_{shd,i} \tag{2}$$

where

Symbol	Meaning	Unit
$E_{before}$	the running total of the loss diagram before this row	kWh/m²
$E_{after}$	the running total after this row	kWh/m²
$E_{row}$	the row taken as a loss	kWh/m²
$\Delta t$	the length of one timestep	hours
$L_i$	the irradiance lost at timestep $i$	W/m²
$s_{m(i)}$	the soiling fraction of the month timestep $i$ falls in	—
$G_{shd,i}$	the plane irradiance after the shading rows	W/m²

Reading the number

A loss, negative. Two percent in most months, with higher winter values at a snowy site, gives about 2.5 % over the year. Dusty sites without cleaning and low-tilt rooftop arrays that the rain does not clean lose more.

API

loss.soiling

Symbols follow the symbol registry.