Real-Time Reliability R&D
NREL's 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.
Real-time reliability R&D focuses on these three primary areas:
- Failure analysis
- Outdoor Testing PV Modules and Small Systems
- Remote Testing and Monitoring of Larger Systems.
Failure Analysis for Photovoltaic Reliability
NREL has equipment and expertise for failure analysis of modules and components. Primary techniques for analyzing modules include light and dark current-voltage measurements, visual inspection, and infrared and electroluminescent imaging.
More detailed analyses of materials and devices are completed through NREL's Measurements and Characterization group.
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 Outdoor Test Facility (OTF). An example of degradation rates measured for these modules is available. Numerous studies have shown that degradation rates for silicon modules are typically less than 1%/yr. NREL's OTF contains a mixture of types of modules, with 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 limited to 600 V; in Europe, some systems are now installed with higher voltages. 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. This data may be viewed at http://maps.nrel.gov/pvdaq/
PV Module Field Failure Database
To complement these activities, NREL has developed a PV Module Field Failure Database. Deployments of small- and mid-sized PV systems have occurred for decades. The pace of these installations—along with their size and sophistication—has picked up dramatically during the last several years. Along with the increasing maturity of PV systems comes a corresponding increase in customer expectations for long-term reliability.
Through the database, PV installers, small-installation owners, and even homeowners can input data on the types of failures they've experienced in their modules and any degradation in performance over time. The degradation can include visually obvious failures as well as unexplained performance drops.
Outdoor Testing PV Modules and Small Systems for Photovoltaic Reliability
In the array field next to NREL's Outdoor Test Facility, data are logged from small (~1 kW) grid-tied systems. Individual modules may be monitored continuously or deployed under various bias conditions with periodic current-voltage measurement. Meteorological data are also logged. All 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.
The OTF does not have space for large PV systems, but NREL has a membership with the Solar Technology Acceleration Center (SolarTAC) and is developing a test field at that site for larger PV systems. Solar TAC is an industry-owned test bed for solar technologies and welcomes new members. Solar TAC members may negotiate with NREL for monitoring of PV systems installed at Solar TAC.
Remote Testing and Monitoring of Larger Systems for Photovoltaic Reliability
As the number of photovoltaic (PV) installations has grown, it becomes relevant and practical to expand outdoor testing to customer-sited PV systems. NREL is implementing the ability to remotely monitor PV systems throughout the United States. The data will be logged directly into the same database that is currently used for the on-site data systems, allowing implementation of automated standard analysis of the data.