pvperfsolar performance modeling

Reference

API field

Soiling loss factor

Share of the light lost to dirt and snow on the modules, per month

Unit %, 12 monthly values

What it is

Soiling is the light lost to dust, pollen and snow on the module glass. The model uses twelve monthly fractions and removes that share of the plane irradiance in each month.

Typical values and how to get it

Typical values: 2 % at a rainy temperate site, 3 to 5 % in dusty or agricultural surroundings, and 5 to 10 % in winter months with snow cover. Replace an estimate with site measurements when you have them.

How the estimate works. The estimate button reads the monthly mean ambient temperature of the weather file and gives each month a snow fraction: 0 for a month at 1.5 °C or warmer, 1 for a month at −3.5 °C or colder, and linear in between. The proposed soiling is 2 % plus 6 % times the snow fraction, and the proposed albedo 0.20 plus 0.45 times it (the first line under How it is applied). The rule is this tool's own and has no published source. If not given: 0 in every month: no soiling.

How it is applied

sm=min⁡(1,max⁡(0,1.5−Tˉm5)),fsoil,m=0.02+0.06 sm,albedom=0.20+0.45 smGafter=(1−fsoil,m) Gbefore\begin{gathered} s_m = \min\left(1, \max\left(0, \frac{1.5 - \bar T_m}{5}\right)\right), \qquad f_{\text{soil},m} = 0.02 + 0.06\, s_m, \qquad \text{albedo}_m = 0.20 + 0.45\, s_m \\ G_{\text{after}} = (1 - f_{\text{soil},m})\,G_{\text{before}} \end{gathered}

where

Symbol Meaning Unit
sms_m the snow fraction of month mm of the estimate —
Tˉm\bar T_m the mean ambient temperature of month mm in the weather file °C
fsoil,mf_{\text{soil},m} this input's value for month mm, as a fraction; the estimate proposes the first line —
albedom\text{albedo}_m the albedo the estimate proposes for month mm —
GafterG_{\text{after}} each plane irradiance component after soiling W/m²
GbeforeG_{\text{before}} the same component after the near shading W/m²

References

  1. Kimber, Mitchell, Nogradi & Wenger 2006, The effect of soiling on large grid-connected photovoltaic systems in California and the Southwest region of the United States, IEEE 4th World Conference on Photovoltaic Energy Conversion
  2. Marion, Schaefer, Caine & Sanchez 2013, Measured and modeled photovoltaic system energy losses from snow for Colorado and Wisconsin locations, Solar Energy 97 112–121
  3. Dobos 2014, PVWatts Version 5 Manual, NREL/TP-6A20-62641

API

site.soiling_monthly — sent as a fraction 0–1

Symbols follow the symbol registry.