David Fredric Joel Kavulak

Validation of the PVLife model using 3 million module-years of live site data

Establishing a strong basis for confidence in a solar technology requires being able to prove a low-degradation track record in the real world, and rationalize it with strong physical understanding and investigation. This paper briefly reviews our previously-published physical model for calculating degradation and reliability, PVLife, which computes hour-by-hour degradation of PV modules using weather files and degradation sub-models developed from accelerated test data. We then demonstrate a validation of this model against a large statistical data set obtained from 266 systems powered by SunPower modules (data from over 179 systems installed by Powerlight, using non-SunPower modules are also shown). In total these data represent over 800,000 modules and a total of 3.2 million module-years of experience. The data analysis technique requires little manual data processing and can be derived from live sites without special experimental treatment. We also discuss returnrate data on modules incorporating SunPowers back-contact cell, as well as front contact modules in SunPowers fleet. Implications for failure prediction are discussed.

PVLife: An integrated model for predicting PV performance degradation over 25+ years

We report results of an integrated model called PVLife that predicts the performance and degradation of a PV system over its entire lifetime. The model solves the coupled electro-thermal equations to calculate PV panel performance for a given set of weather conditions. Based on this calculated operating point and a series of physical sub-models for key degradation and failure modes, the progressive degradation of the panel performance is simulated, creating a second level of coupling. The sub-models describing the different degradation modes are developed based on data from the field and accelerated laboratory tests. To close the loop, the overall model is compared with both laboratory and field data. Coupled degradation modes, including possible feedback loops, are investigated.