Comparative Analysis of Change-Point Techniques for Nonlinear Photovoltaic Performance Degradation Rate Estimations

A linear performance drop is generally assumed during the photovoltaic (PV) lifetime. However, operational data demonstrate that the PV module degradation rate (
Rd
) is often nonlinear, which, if neglected, may increase the financial uncertainty. Although nonlinear behavior has been the subject of numerous publications, it was only recently that statistical models able to detect change-points and extract multiple
Rd
values from PV performance time-series were introduced. A comparative analysis of six open-source libraries, which can detect change-points and calculate nonlinear
Rd
, is presented in this article. Since the real
Rd
and change-point locations are unknown in field data, 960 synthetic datasets from six locations and two PV module technologies have been generated using different aggregation and normalization decisions and nonlinear degradation rate patterns. The results demonstrated that coarser temporal aggregation (i.e., monthly vs. weekly), temperature correction, and both PV module technologies and climates with lower seasonality can benefit the change-point detection and
Rd
extraction. This also raises a concern that statistical models typically deployed for
Rd
analysis may be highly climatic- and technology-dependent. The comparative analysis of the six approaches demonstrated
median
mean absolute errors (MAE) ranging from 0.06 to 0.26%/year, given a maximum absolute
Rd
of 2.9%/year. The
median

MAE
in change-point position detection varied from 3.5 months to 6 years.