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 two primary areas:
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/. In particular, one of the data sets available through the PVDAQ photovoltaic performance database is high-accuracy community-shared data for a large PV plant in North Carolina. This PV system performance data set is intended for modelers to use for validating models.
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.