Photovoltaic Performance

NREL scientists study the long-term performance, reliability, and failures of photovoltaic (PV) components and systems in-house and via external collaborations. Through analysis, they quantify long-term degradation and share the results with the PV community.

Tools and Capabilities

  • Failure Analysis for PV Reliability
    NREL has equipment and expertise to perform failure analysis of modules and components. Primary techniques for analyzing modules include light and dark current-voltage (I-V) measurements, visual inspection, and infrared and electroluminescent imaging. More detailed analyses of materials and devices are completed through our device performance activities.

  • Outdoor Testing PV Modules and Small Systems for PV Reliability
    In the array field adjacent to the Outdoor Test Facility (OTF), data are logged from small (1–3-kW) grid-tied systems. Individual modules may be monitored continuously or deployed under various bias conditions with periodic I-V measurement. Meteorological data are also logged. Data are managed in a database with automated standardized calculations for quality assurance and performance determination. The data are analyzed in more detail for publication.

    • Long-Term Monitoring
      A primary concern in the PV community is quantifying degradation and failure rates in the field. NREL  is studying long-term performance of more than 100 modules at its OTF. Numerous studies have shown that degradation rates for silicon modules are typically less than 1%/yr. NREL's OTF contains various types of modules, with an emphasis on new technologies; but some modules or small systems have been monitored for more than 10 years.

    • High-Voltage Bias
      A potential problem with monitoring of modules is that degradation and failure rates may be affected by operation at high voltage. In the United States, system voltages are typically limited to 600 volts, but higher voltages are also being used. NREL is studying the effects of application of voltage in the field, quantifying leakage currents, and watching for correlation between the applied voltage and the observed degradation/failure rates.

    • Studies Outside of Colorado
      NREL is collecting data from PV systems around the country with the goal of capturing the bigger picture of how degradation and failure rates may vary with location through the PVDAQ photovoltaic performance database.

  • Thin-Film PV Characterization
    This work uses forward bias as a preconditioning technique to address the meta-stabilities of polycrystalline thin-film (CdTe and CIGS) PV modules when measuring their peak power using a solar simulator. Light exposure can also be used to precondition modules before characterization using an Atonmetrics light chamber or outdoor exposure.

Data Sets

NREL has collected PV performance data sets for use by the community. These sets complement our solar resource data.

Shared Data Set for Flat-Plate PV Module Model Validations

This project developed a comprehensive data set of measured I-V curves and associated meteorological data for PV modules representing all flat-plate PV technologies and for the weather conditions of three climatically different locations: Colorado, Florida, and Oregon. The data set contains more than 1 million I-V curves. The data set is publicly available, and for the first time, it will allow researchers to develop and validate PV module performance models using commonly available and quality-assessed data. See the user's manual for information on the content and format of the data set. To access the data, contact Bill Marion for FTP instructions.

Data Sets for PV Systems in the United States

Some of the data from multiple PV systems in the U.S. are screened for accuracy; but most of the data are not screened, so users should clean the data as part of the standard analysis. Data may be viewed through an interactive graphing capability or downloaded for analysis.


Current activities are funded by the Department of Energy's Office of Energy Efficiency and Renewable Energy and include:


NREL publishes PV reliability journal articles, technical reports, conference papers, and outreach documents. 

Michael Deceglie: Thin-film module measurements, and outdoor studies

Dirk Jordan: Statistical analysis of PV outdoor performance

Bill Marion: Solar radiation resource information, and PV module and system performance modeling

Matt Muller: CPV performance, and reliability and soiling