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Real-Time Photovoltaic and Solar Resource Testing

National Center for Photovoltaics (NCPV) scientists and engineers study long-term performance, reliability, and failures of PV components and systems—both in house and via external collaborations. Through analysis, they quantify long-term degradation and then share the results with the PV community.

Tools and Capabilities

  • Failure Analysis for PV Reliability. The NCPV 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 NCPV's Device Performance group.

  • Outdoor Testing PV Modules and Small Systems for PV Reliability. In the array field adjacent to the NCPV's 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. The NCPV 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. The NCPV 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. The NCPV 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.

  • CPV Characterization
    A test bed is available for testing concentrator photovoltaic (CPV) modules. The tracker provides high accuracy (better than ±0.5°), and automated I-V curve tracing is available.

  • 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

The NCPV has collected PV performance data sets for use by the community. These sets complement the solar resource data that are available.

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/or 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 the 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 Energy Efficiency and Renewable Energy (EERE) Office including the following SuNLaMP projects:

Standards Development for Photovoltaic Reliability. In collaboration with PVQAT, the NCPV is supporting the development of comprehensive standards for PV reliability using a three-pronged strategy focused on:

  • Establishing qualification methods for durability of PV module design with a chosen climate and mounting system;

  • Developing a guide for auditing quality management systems toward consistent manufacturing of PV modules built to that design;

  • Ensuring adequacy of design, installation, and operation through a certification process for system verification.

Laboratory personnel participate in writing and discussing reliability, safety, and test and evaluation standards—primarily with IEC Technical Committee 82 (Working Groups 2, 3, 6, and 7), but also with a number of other standards organizations including the American Society for Testing and Materials (ASTM), Underwriters Laboratories, and TUV Rheinland. This work is done in partnership with Solar ABCs. NCPV researchers work through the International Photovoltaic (PV) Quality Assurance (QA) Task Force to effectively leverage the knowledge of the broader PV community toward developing comprehensive PV standards.

Each year, NCPV researchers, along with solar companies and other national lab researchers, participate in an industry workshop on PV reliability, conducted to encourage exchange of information about PV reliability. Proceedings of past workshops are available.

Photovoltaic Reliability Publications

The NCPV publishes PV reliability journal articles, technical reports, conference papers, and outreach documents. The following NCPV publications can be found on the following topics by clicking on the names of the researchers below.

  • 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