DOE, Industry Develop Software For Calculating Solar PV Degradation Rates


A new software package developed by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and industry partners SunPower and kWh Analytics is designed to improve the measurement of a solar PV system’s expected lifetime performance.

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, says NREL.

“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,” says 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.”

According to NREL, solar PV module and system degradation have been historically difficult to assess. Field performance can be impacted by many confounding variables, including ambient weather conditions, seasonal changes, sensor drift and soiling, to name a few. Extracting system degradation rates previously required years of production data, high-accuracy instrumentation, and the presence of staff scientists to conduct the evaluation, the lab explains.

NREL says the RdTools software package solves these problems by providing a validated software toolkit for calculating and analyzing PV system performance and degradation over time. The tool can deliver valuable insights 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 neighboring systems.

“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,” says Greg Kimball, a senior performance engineer at SunPower, co-developer of the software. “The result prompted improvements to and extension of our warranty coverage to customers.”

RdTools was led by a NREL team of researchers – Michael Deceglie, Chris Deline, Dirk Jordan and Ambarish Nag – and funded by the DOE’s Solar Energy Technologies Office. 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 contact NREL at or visit the website here.

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