Comparison of Pyranometers and Reference Cells on Fixed and One-axis Tracking Surfaces

F. Vignola, Josh Peterson, Chun Yu Chiu, Michael Dooraghi, Manajit Sengupta, Fotis Mavromatakis

Research output: Contribution to conferencePaperpeer-review

7 Scopus Citations


Photovoltaic (PV) system perfomance is monitored by a wide variety of sensors. These instruments range from secondary standard pyranometers to photodiode-based pyranometers to reference cells. Although instruments are mounted in the plane of array of the modules a wide range of results have been obtained. Some of these difference have been assumed to come from systematic uncertainties associated with the irradiance sensors. This study is an attempt to quantify these differences by comparing the output of selected thermopile-based pyranometers to photodiode-based pyranometers and reference cells on a horizontal surface, a fixed-Tilt surface, and a one-Axis tracking surface. This analysis focuses on clear-sky results from two sites with different climatic conditions. Several important features were observed. Photodiode-based pyranometers and reference cells produce widely different results under clear skies, especially at larger angles-of-incidence even though both instruments are based on measuring the short circuit current of solar cells. The difference is caused by the scattering of light as it passes through the glazing of the reference cell or the diffuser lens of the photodiodedbase pyranometer. Both instruments are shown to have similar response to the spectral distribution of the irradiance when compared to the thermopile-based pyranometer that has a response nearly independent of the wavelength of light used by PV modules.

Original languageAmerican English
Number of pages10
StatePublished - 2017
Event46th ASES Annual National Solar Conference, SOLAR 2017 - Denver, United States
Duration: 9 Oct 201712 Oct 2017


Conference46th ASES Annual National Solar Conference, SOLAR 2017
Country/TerritoryUnited States

Bibliographical note

See NREL/CP-5D00-70285 for preprint

NREL Publication Number

  • NREL/CP-5D00-71028


  • Measurements
  • One-Axis Tracking
  • Pyranometer
  • Reference Cell
  • Solar


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