"Soiling, Cleaning, and Abrasion: The Results of the Five-Year Photovoltaic Glass Coating Field Study"

Joanna Bomber, Asher Einhorn, Chaiwat Engtrakul, Clare Lanaghan, Jeffrey Linger, Leonardo Micheli, David Miller, Joshua Morse, Helio Moutinho, Matthew Muller, Jimmy Newkirk, Lin Simpson, Bobby To, Sarah Toth, Telia Curtis, Fang Li, Govindasamy Tamizhmani, Sai Tatapudi, Vivian Alberts, Aaesha Al NuaimiPedro Banda, Jim John, Gerhard Mathiak, Ahmad Safieh, Marco Stefancich, Bader Alabdulrazzaq, Ayman Al-Qattan, Sonali Bhaduri, Anil Kottantharayil, Ben Bourne, Zoe deFreitas, Fabrizio Farina, Greg Kimball, Adam Hoffman

Research output: NRELPresentation


External contamination ("soiling") of the incident surface is a major limiting factor for solar technologies. A 5-year field glass coupon study was conducted to better understand external contamination and its effects; compare cleaning methods and the use of preventative coatings; and explore the abrasion resulting from cleaning to advise on accelerated abrasion testing. Test sites included the cities of Dubai (UAE), Kuwait City (Kuwait), Mesa (AZ), Mumbai (India), and Sacramento (CA). Through the 5-year cumulative study, dry brush, water spray, and wet sponge and squeegee cleaning methods were compared to no cleaning. Optical microscopy was used to obtain images, including representative color images, grayscale images for object analysis, and oblique images for coating integrity assessment. A thresholding protocol was developed to analyze and distinguish specimens using the ImageJ software. Optical performance was quantified using a spectrophotometer, including comprehensive optical characterization (transmittance, reflectance, and absorptance in addition to forward- and back-scattering). Atomic force microscopy was used to verify the abrasion damage morphology, including the width and depth of surface scratches. Analysis of the results included correlation of optical performance and particle area coverage, rank order (by coating or location), and the acceleration factor for abrasion damage. The efficacy of external cleaning was more readily distinguished from the effectiveness of antisoiling coatings. The acceleration factor for dry brush cleaning of a porous silica coating was found to be on the order of unity.
Original languageAmerican English
Number of pages34
StatePublished - 2024

NREL Publication Number

  • NREL/PR-5K00-90174


  • antireflective (AR) coating
  • antisoiling (AS) coating
  • atomic force microscopy (AFM)
  • cleaning
  • contamination density
  • durability
  • ImageJ
  • optical performance
  • particulate matter
  • PV Quality Assurance Task Force (PVQAT)
  • soiling
  • surface abrasion
  • surface coverage


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