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To take the closeup of the test glass after the end of the test period (Jan-Mar), we placed a plastic transparency with the zero (2 mm by 3.5 mm) under the test glass to show scale. Under that layer is a white EVA sheet backing. Illumination was from the right at low incidence angle from afternoon sunlight. The magnification in the photo we've included here is 15x. Images taken at higher magnifications indicate that both types of particles are in the range of 1 to 20 micrometers in diameter.

As can be seen, there are two types of particles, black and white. From other analysis, and from the urban location of the collection site, it is likely that the black particles are soot and automobile hydrocarbon deposits. The nature of the white particles is unknown, but the site received a great deal of rain and condensation over the testing period (Jan.-Mar. 2017), and so it is likely that these represent the precipitated dissolved salts found in the atmosphere. Further analysis and testing is underway.

PV Quality and PV Soiling

lamp set up to illuminate plates for determining hemispheric transmittance of the glass

Measurement set-up for determining the hemispherical transmittance of the glass.
Photo: Greg P. Smestad

Sol Ideas News

Keep up with Greg P. Smestad and Sol Ideas Technology Development. News includes new publications, research projects, seminars, conferences, interviews and events »

Researcher Greg Smestad setting up the glass samples for the experiment

Researcher Greg Smestad setting up the 6 glass samples.

magnified view of surface of glass

A 15x view of the surface of the glass after the 8 week study; the '0' is 2 mm by 3.5 mm. - more
Photo: Greg P. Smestad.

soiled glass plates used in study

Soiled glass plates at the end of the study illuminated by sunlight coming in from the right side.
Photo: Greg P. Smestad


The accumulation of soiling on photovoltaic (PV) modules affects PV systems worldwide. Soiling consists of mineral dust, soot particles, aerosols, pollen, fungi and other contaminants that deposit on the surface of PV modules. Soiling absorbs, scatters, and reflects a fraction of the incoming sunlight, reducing the intensity that reaches the active part of the solar cell. Here, we provide some resources on the topic, as well as some presentations and publications in which Greg P. Smestad and Sol Ideas Technology Development have been involved.

PV Soiling: Selected Publications

  • 2017 June 25-30 - A unique global investigation on the spectral effects of soiling losses of PV glass substrates: preliminary results; L. Micheli, E. F. Fernández, G. P. Smestad, et al., 2017 IEEE PVSC-44, Washington, D.C.   Download Paper    Download Poster.   Visit conference website at ieee-pvsc.org/PVSC44/. This is the progenitor for all of the work that Greg P. Smestad, Eduardo F. Fernández, and Leonardo Micheli published subsequently. It utilized somewhat problematic transmission data from the Perkin Elmer Lambda spectrometer. The main conclusions, however, have remained and are sound.
  • 2017 Jun 29 - Chemistry, materials science and technology related to photovoltaic, and photoelectrochemical solar energy conversion. Presented as part of the USPTO's Patent Examiner Technical Training Program; G. P. Smestad - View Presentation on Slideshare.
  • 2017 October 23-25, 2017 - International PV Soiling Workshop, Dubai World Trade Center, Dubai United Arab Emirates, hosted by the Electricity & Water Authority (DEWA) Research and Development Centre, and the U.S. National Renewable Energy Laboratory (NREL), Waveband analysis for understanding the soiling impact on PV systems; E. F. Fernández - Download Presentation An acknowledgement of Sol Ideas Tech. Dev., NREL and other collaborators was made at the end of the slides.
  • 2017 Dec 6 - Optical Characterization of PV Glass Coupons and PV Modules Related to Soiling Losses, Atlas/NIST Workshop on PV Materials Durability; G. P. Smestad, L. Micheli, T. A. Germer, E. F. Fernández - View Presentation.
  • 2018 March 14 - Optical Characteristics of PV Glass Coupons and PV Modules Related to Soiling Losses, IEEE Santa Clara Valley PhotoVoltaic Joint Society Chapter; G. P. Smestad, L. Micheli, T. A. Germer, E. F. Fernández - View Presentation.
  • 2018 April 16-18 - Investigating the spectral nature of soiling and its impact on multi-junction CPV systems, 14th International Conference on Concentrator Photovoltaics (CPV-14) Puertollano, Spain; E. F. Fernández, F. M. Almonacid, L. Micheli, G. P. Smestad, M. Muller - Download Presentation
  • 2018 May 08 - Optical Characterization of PV Glass Coupons and PV Modules Related to Soiling Losses; G. P. Smestad, L. Micheli, T. A. Germer, E. F. Fernández, PVQAT Soiling and Dust: Task Group 12 webinar.  
    Download Presentation
  • 2018 May 14 - Optical Characterization of PV Glass Coupons and PV Modules Related to Soiling Losses; G. P. Smestad, L. Micheli, T. A. Germer, CLEO: OSA Nanophotonics Technical Group 20x20 Talks; San José Convention Center, San José, California. Download Presentation
  • 2018 September 23-28 - Design and Indoor Validation of DUSST: A Novel Low-Maintenance Soiling Station; M. Muller, J. Morse, F. Almonacid, E. Fernadez, L. Micheli in 35th European PV Solar Energy Conference & Exhibition (EU PVSEC), Brussels, Belgium. Preprint available from National Renewable Energy Laboratory, Golden, CO: NREL/CP-5K00-71216. The text includes, "A 2D drawing of the DUSST design, described in the provisional patent submitted to the U.S. Patent and Trademark Office [9], is shown in Figure 1." Note references 9, 11 and 12.  
  • 2018 October 30 - November 1, 2018 - EQE Soiling Ratio and Transmission Losses; G. P. Smestad, T. Moriarty, L. Micheli, L. Simpson, B. Hamadani, T. A. Germer, G.S. TamizhMani (Mani), J. Oh, 2018 International PV Soiling Workshop, Denver Marriott West Hotel, Golden, Colorado.  
  • 2019 May 16 - L. Micheli, J. A. Caballero, E. F. Fernandez, G. P. Smestad, G. Nofuentes, T. K. Mallick, F. M. Almonacid, "Correlating photovoltaic soiling losses to waveband and single-value transmittance measurements," Energy, 180, 376-386, 2019. Download Paper   Read Online via article's DOI.
  • 2020 January 09 - G. P. Smestad, T. A. Germer, H. Alrashidi, et al.,“Modelling photovoltaic soiling losses through optical characterization,” Sci. Rep. 10:58, 2020.
    Download Paper - Read Online via article's DOI - Download the Supplementary information - View Mendeley data repository
  • 2020 April 20 - L. Micheli, E. F. Fernández, M. Muller, G. P. Smestad, F. M. Almonacid, "Selection of optimal wavelengths for optical soiling modelling and detection in photovoltaic modules," Sol. Energy Mat. and Sol. Cells, 212, Article 110539, 2020.
    Download Paper - Read Online via article's DOI
  • 2021 October 18 - L. Micheli, G. P. Smestad, J. G. Bessa, M. Muller, E. F. Fernández and F. Almonacid, "Tracking Soiling Losses: Assessment, Uncertainty, and Challenges in Mapping," in IEEE Journal of Photovoltaics, vol. 12, no. 1, pp. 114-118, Jan. 2022, doi: 10.1109/JPHOTOV.2021.3113858. Download paper via ResearchGate
  • H. Brahma, S. Pant, L. Micheli, G. P. Smestad, N. Sarmah, “Effect of Environmental Factors on Photovoltaic Soiling: Experimental and Statistical Analysis,” Energies 16, article 45, 2023.
    Download Paper - Read Online via article's DOI - The supporting information can be downloaded here - This article belongs to the Special Issue on Photovoltaics and Energy-Storage Applications.
  • Refer to the publications page for a selection of related papers by Dr. Greg Smestad.
  • Refer to Presentations for a list of selected presentations by Greg Smestad.

PV Soiling: Other Groups

  • Using the formalism described in the following paper, an estimation of wavelength dependent soiling and dust losses in photovoltaic modules can be made: Bergin, M. H., Greenwald, R., Xu, J., Berta, Y. and Chameides, W. L. (2001), "Influence of aerosol dry deposition on photosynthetically active radiation available to plants: A case study in the Yangtze Delta Region of China". Geophys. Res. Lett., 28: 3605–3608.   Download Paper   Read Online via article's DOI.
  • This has been done in "Large Reductions in Solar Energy Production Due to Dust and Particulate Air Pollution", Mike H. Bergin, Chinmay Ghoroi, Deepa Dixit, James J. Schauer, and Drew T. Shindell, Environ. Sci. Technol. Lett., 2017. Read Online via article's DOI.
  • Solarplaza's complimentary whitepaper on the topic of soiling: Soiling - The Science & Solutions; Download Paper.
  • 2017 Oct 11 - Webinar recording - Quantification of Module Soiling: Data Analysis and Innovative Methods; Donald van Velsen of Kipp & Zonen B.V. and Gerhard Mütter of Alternative Energy Solutions GmbH - View Presentation.


PVQAT (pron. "pee vee cat") hosts webinars that are designed to facilitate international collaboration regarding soiling in PV and CSP systems. Learn more


  • Watch : PV - Cleaning & Soiling (compiled by Elias Urrejola)
  • Watch : Soiling Assessment in Large-Scale PV Arrays (from Swinerton Renewable Energy)

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