Uncertainty of Rotating Shadowband Irradiometers and Si-Pyranometers Including the Spectral Irradiance Error

Aron Habte, Stefan Wilbert, Stefan Kleindiek, Bijan Nouri, Norbert Geuder, Marko Schwandt, Frank Vignola

Research output: Contribution to conferencePaperpeer-review

31 Scopus Citations

Abstract

Concentrating solar power projects require accurate direct normal irradiance (DNI) data including uncertainty specifications for plant layout and cost calculations. Ground measured data are necessary to obtain the required level of accuracy and are often obtained with Rotating Shadowband Irradiometers (RSI) that use photodiode pyranometers and correction functions to account for systematic effects. The uncertainty of Si-pyranometers has been investigated, but so far basically empirical studies were published or decisive uncertainty influences had to be estimated based on experience in analytical studies. One of the most crucial estimated influences is the spectral irradiance error because Si-photodiode-pyranometers only detect visible and color infrared radiation and have a spectral response that varies strongly within this wavelength interval. Furthermore, analytic studies did not discuss the role of correction functions and the uncertainty introduced by imperfect shading. In order to further improve the bankability of RSI and Si-pyranometer data, a detailed uncertainty analysis following the Guide to the Expression of Uncertainty in Measurement (GUM) has been carried out. The study defines a method for the derivation of the spectral error and spectral uncertainties and presents quantitative values of the spectral and overall uncertainties. Data from the PSA station in southern Spain was selected for the analysis. Average standard uncertainties for corrected 10 min data of 2 % for global horizontal irradiance (GHI), and 2.9 % for DNI (for GHI and DNI over 300 W/m2) were found for the 2012 yearly dataset when separate GHI and DHI calibration constants were used. Also the uncertainty in 1 min resolution was analyzed. The effect of correction functions is significant. The uncertainties found in this study are consistent with results of previous empirical studies.

Original languageAmerican English
Number of pages11
DOIs
StatePublished - 31 May 2016
Event21st International Conference on Concentrating Solar Power and Chemical Energy Systems, SolarPACES 2015 - Cape Town, South Africa
Duration: 13 Oct 201516 Oct 2015

Conference

Conference21st International Conference on Concentrating Solar Power and Chemical Energy Systems, SolarPACES 2015
Country/TerritorySouth Africa
CityCape Town
Period13/10/1516/10/15

Bibliographical note

Publisher Copyright:
© 2016 Author(s).

NREL Publication Number

  • NREL/CP-5D00-66651

Keywords

  • data analysis
  • error analysis
  • infrared spectra
  • irradiance
  • visible spectra

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