Accurately predicting the longevity of photovoltaic (PV) panels is essential to increase energy production and lower costs. PV module and system degradation have been historically difficult to assess in the industry as performance can be impacted by many variables including ambient weather conditions, seasonal changes, sensor drift and soiling. Extracting system degradation rates previously required years of production data, high accuracy instrumentation and the presence of staff scientists to conduct the evaluation.
The team from NREL and its partners created a modelling tool called RdTools that shows time-series data along with a year-on-year degradation distribution. The same system is analyzed with the clear-sky method (a, above) and sensor-based method with a poorly maintained sensor (b). This clearly shows that high reported degradation is likely caused by sensor drift rather than a degrading PV module.
RdTools combines best practices with years of NREL degradation research to deliver new methodologies that change how solar field production data is evaluated. The software package makes it possible to accurately evaluate PV systems faster, despite common challenges with performance data.
“There’s a high level of interest in this software because it provides user-friendly, accurate, and objective assessments that can help owners make sense of their data,” said Dirk Jordan, engineer and solar PV researcher at NREL. “We spent years building consensus in the industry around a common set of analytical rules. Now PV stakeholders can learn much more about the performance of their technology and improve decision-making on multiple fronts.”
RdTools provides a robust and validated software toolkit for calculating and analyzing PV system performance and degradation over time. The tool can provide key data for manufacturers, engineers, investors and owners who have a stake in system performance, such as identifying under-performing sub-arrays, and quantifying system performance relative to neighbouring systems.
For co-developer SunPower, the results of its own data analysis were signficant. “The RdTools method was used to analyze energy generation from 264 PV systems at locations across the globe, revealing that degradation rates were slower than expected,” said Greg Kimball, a senior performance engineer at SunPower. “The result prompted improvements to and extension of our warranty coverage to customers.”
The software is actively being developed as a set of open-source Python scripts and usage examples on GitHub and is publicly available to interested users who can access, download, and customize the software.
Organizations interested in testing and contributing to the software can visit www.nrel.gov/pv/rdtools.html