Masking of Photovoltaic System Performance Problems by Inverter Clipping and Other Design and Operational Practices

Andy Walker, John Balfour, Roger Hill, Gerald Robinson, Thushara Gunda, Jal Desai

Research output: Contribution to journalArticlepeer-review

6 Scopus Citations


This paper describes how performance problems can be “masked,” or not readily evident by several causes: by photovoltaic (PV) system configuration (such as the size of the PV array capacity relative to the size of the inverter and the resultant clipped operating mode); by instrumentation design, installation, and maintenance (such as a misaligned or dirty pyranometer); by contract clauses (when operational availability is transformed to contractual availability, which excludes many factors); and by identified management and operational practices (such as reporting on a portfolio of plants rather than individually). A simple method based on a duration curve is introduced to overcome shortcomings of Performance Ratio based on nameplate capacity and Performance Index based on hourly simulation when quantifying masking effects, and inverter clipping and pyranometer soiling are presented as two examples of the new method. With a better understanding of the non-transparency of masking issues, stakeholders can better interpret performance data and deliver improved AC and DC plant conditions through PV system operation and maintenance (O&M) for improved performance, reduced O&M costs, and a more consistently delivered, and reduced, levelized cost of energy (LCOE).

Original languageAmerican English
Article number111067
Number of pages8
JournalRenewable and Sustainable Energy Reviews
StatePublished - Jul 2021

Bibliographical note

Publisher Copyright:
© 2021 Elsevier Ltd

NREL Publication Number

  • NREL/JA-5C00-76012


  • AC/DC ratio
  • Availability
  • Inverter clipping
  • Inverter saturation
  • Masking
  • Operation and maintenance (O&M)
  • Performance ratio
  • Photovoltaic system performance


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