Soiling and self-cleaning of PV modules in the arid climate of Tempe, Arizona

1. Werner Herrmann, Markus Schweiger
TÜV Rheinland Energie und Umwelt GmbH, Am Grauen Stein, 51105 Cologne, Germany
Email: werner.herrmann@de.tuv.com
Soiling and self-cleaning of PV modules
in the arid climate of Tempe, Arizona
Besides the site conditions, the glazing characteristics of PV modules can be a dominating factor for performance losses
of PV power systems if operated in climates with high dust concentration. For example, any surface texturing will support
dust settlement and lead to higher soiling losses. Also the question is unanswered whether glass types with anti-reflective
coating show a favorable soiling and the self-cleaning behavior compared to standard glass. To quantify transmission
differences for various PV glass types caused by soiling, we studied the energy yield performance of three c-Si PV
modules, which were identical in construction and materials, except the cover glass.
This work was partially funded by the German Federal Ministry for
Economic Affairs and Energy (BMWi) as part of contract no. 0325517B.
Standard glass AR coated glass
deep textured glass with
pyramidal structureExperimental approach:
 Synchronous measurement of I-V curves with 10 minutes data
recoding interval over a period of one year at test location Tempe,
Arizona.
 Calculation of effective irradiance reaching the cells
where:
ISC,MOD = measured short circuit current
ISC,STC = Calibrated ISC at STC
TBoM = Back of module temperature
 = ISC temperature coefficient
 Transmission differences due to soiling and self-cleaning between
glass types were concluded from the ratio of effective irradiances.
 Angular impacts on soiling losses were analyzed by data filtering for
plane of array irradiance (GPOA) and angle of incidence of direct
sunlight (AoI):
a) No angular impact: GPOA>900 W/m² and AoI<40°
b) Full range angular impact: GPOA >50 W/m²
Figure 1: Effective irradiances of AR coated glass
and deep textured glass related to standard glass
Figure 2: Impact of soiling on angular
transmittance of AR coated glass related to
standard glass
Figure 3: Impact of soiling on angular
transmittance of deeply textured glass
compared to standard glass
Deep textured glass
(pyramidal structure)
Results:
 AR coated glass: The soiling and self-cleaning behavior is
comparable to standard glass (Figure 1). Angular performance gains
for AoI > 50° result in +0.9% annual transmission gain (Figure 2).
 Deep textured glass: Significant transmission losses were observed
due higher dust settlement (Figure 1). Annual transmission loss due
to soiling (-1.8%) compensates partially the transmission gains due
to better angular response (+3.9%).