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Title: Reducing Interanalyst Variability in Photovoltaic Degradation Rate Assessments

Abstract

The economic return on investment of a commercial photovoltaic system depends greatly on its performance over the long term and, hence, its degradation rate. Many methods have been proposed for assessing system degradation rates from outdoor performance data. However, comparing reported values from one analyst and research group to another requires a common baseline of performance; consistency between methods and analysts can be a challenge. An interlaboratory study was conducted involving different volunteer analysts reporting on the same photovoltaic performance data using different methodologies. Initial variability of the reported degradation rates was so high that analysts could not come to a consensus whether a system degraded or not. More consistent values are received when written guidance is provided to each analyst. Further improvements in analyst variance was accomplished by using the free open-source software RdTools, allowing a reduction in variance between analysts by more than two orders of magnitude over the first round, where multiple analysis methods are allowed. This article highlights many pitfalls in conducting 'routine' degradation analysis, and it addresses some of the factors that must be considered when comparing degradation results reported by different analysts or methods.

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [5];  [6]; ORCiD logo [7];  [8]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [9]; ORCiD logo [10];  [11];  [11]; ORCiD logo [11]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. National Univ. of Singapore (Singapore)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  4. Univ. of Utah, Salt Lake City, UT (United States)
  5. Stanford Univ., CA (United States)
  6. Case Western Reserve Univ., Cleveland, OH (United States)
  7. Canadian Solar, Suzhou (China)
  8. Technological Education Inst. of Crete, Heraklion (Greece)
  9. SunPower Corporation, San Jose, CA (United States)
  10. kWh Analytics, San Francisco, CA (United States)
  11. Dubai Electricity & Water Authority, Dubai (United Arab Emirates)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
OSTI Identifier:
1592395
Report Number(s):
NREL/JA-5K00-72879
Journal ID: ISSN 2156-3381; MainId:13079;UUID:1d77b539-63f3-e811-9c19-ac162d87dfe5;MainAdminID:1559
Grant/Contract Number:  
AC36-08GO28308
Resource Type:
Accepted Manuscript
Journal Name:
IEEE Journal of Photovoltaics
Additional Journal Information:
Journal Volume: 10; Journal Issue: 1; Journal ID: ISSN 2156-3381
Publisher:
IEEE
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; degradation rate; photovoltaics; RdTools; round-robin

Citation Formats

Jordan, Dirk C., Luo, Wei, Jain, Anubhav, Saleh, Mashad U., von Korff, Heidi, Hu, Yang, Jaubert, Jean-Nicolas, Mavromatakis, Fotis, Deline, Chris, Deceglie, Michael G., Nag, Ambarish, Kimball, Gregory M., Shinn, Adam B., John, Jim J., Alnuaimi, Aaesha A., and Elnosh, Ammar A. Reducing Interanalyst Variability in Photovoltaic Degradation Rate Assessments. United States: N. p., 2019. Web. doi:10.1109/jphotov.2019.2945191.
Jordan, Dirk C., Luo, Wei, Jain, Anubhav, Saleh, Mashad U., von Korff, Heidi, Hu, Yang, Jaubert, Jean-Nicolas, Mavromatakis, Fotis, Deline, Chris, Deceglie, Michael G., Nag, Ambarish, Kimball, Gregory M., Shinn, Adam B., John, Jim J., Alnuaimi, Aaesha A., & Elnosh, Ammar A. Reducing Interanalyst Variability in Photovoltaic Degradation Rate Assessments. United States. https://doi.org/10.1109/jphotov.2019.2945191
Jordan, Dirk C., Luo, Wei, Jain, Anubhav, Saleh, Mashad U., von Korff, Heidi, Hu, Yang, Jaubert, Jean-Nicolas, Mavromatakis, Fotis, Deline, Chris, Deceglie, Michael G., Nag, Ambarish, Kimball, Gregory M., Shinn, Adam B., John, Jim J., Alnuaimi, Aaesha A., and Elnosh, Ammar A. Fri . "Reducing Interanalyst Variability in Photovoltaic Degradation Rate Assessments". United States. https://doi.org/10.1109/jphotov.2019.2945191. https://www.osti.gov/servlets/purl/1592395.
@article{osti_1592395,
title = {Reducing Interanalyst Variability in Photovoltaic Degradation Rate Assessments},
author = {Jordan, Dirk C. and Luo, Wei and Jain, Anubhav and Saleh, Mashad U. and von Korff, Heidi and Hu, Yang and Jaubert, Jean-Nicolas and Mavromatakis, Fotis and Deline, Chris and Deceglie, Michael G. and Nag, Ambarish and Kimball, Gregory M. and Shinn, Adam B. and John, Jim J. and Alnuaimi, Aaesha A. and Elnosh, Ammar A.},
abstractNote = {The economic return on investment of a commercial photovoltaic system depends greatly on its performance over the long term and, hence, its degradation rate. Many methods have been proposed for assessing system degradation rates from outdoor performance data. However, comparing reported values from one analyst and research group to another requires a common baseline of performance; consistency between methods and analysts can be a challenge. An interlaboratory study was conducted involving different volunteer analysts reporting on the same photovoltaic performance data using different methodologies. Initial variability of the reported degradation rates was so high that analysts could not come to a consensus whether a system degraded or not. More consistent values are received when written guidance is provided to each analyst. Further improvements in analyst variance was accomplished by using the free open-source software RdTools, allowing a reduction in variance between analysts by more than two orders of magnitude over the first round, where multiple analysis methods are allowed. This article highlights many pitfalls in conducting 'routine' degradation analysis, and it addresses some of the factors that must be considered when comparing degradation results reported by different analysts or methods.},
doi = {10.1109/jphotov.2019.2945191},
journal = {IEEE Journal of Photovoltaics},
number = 1,
volume = 10,
place = {United States},
year = {2019},
month = {10}
}

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Figures / Tables:

Fig. 1 Fig. 1: DC power (left axis) of a small and relatively clean test system at NREL that was used in the interlaboratory study. The right axis shows array responsivity including the degradation rate trend.

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.