Solar module lifetime predictions are getting better

NREL has proposed a new methodology for determining solar module degradation rates, taking into account measurement challenges such as sensor drift, inverter nuances, soiling and others – keeping the focus on the solar modules themselves.

Module testing and degradation models are becoming more sophisticated.

Image: NREL SunShot

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From pv magazine USA

SunPower is the  industry leader when it comes to solar module degradation. The company has achieved the lowest warranted degradation rate at 0.25% a year, and after the 25 year solar panel warranty lifetime SunPower projects that the PV modules will be at 92% of their original output. Additionally, 99 out of 100 solar modules are projected to be above 70% of their original output after a 40 year lifetime.

The Department of Energy’s National Renewable Energy Lab (NREL), has aimed to better understand what the real degradation rate of a solar module is in its report Robust PV Degradation Methodology and Application.

NREL noted that many methods have been proposed for extracting the degradation rate from operational data of PV systems, but most of the published approaches are susceptible to bias due to inverter clipping, module soiling, temporary outages, seasonality, and sensor degradation. For instance, the below image shows sensor degradation/drift in the purpose, which would have suggested module degradation, but after filtering the more consistent blue solar production data comes out.

NREL looked at each of the  variables, and tuned the model to account for and remove these variations from the data. NREL then compared this newly filtered field collected data with the many solar systems the research group has had running for longer than 10 years, and now proposes the new analysis technique.

As part of this analysis, SunPower modules showed a field measured degradation rate of 0.2% per year – suggesting a slightly better than 92% productivity after 25 years with the 0.25% degradation warranty.

Recent research grants have set industry eyes on a 50 year lifetime for glass on glass solar modules, and with some power purchase agreements have a 25 year lifetime – with a 25 year option. These goals aren’t unattainable – as Kyocera, back in 2011, showed off a 1991 installation which it says ran with a “near-constant” efficiency level. The company supplied another solar power plant, recently verified, that’s been running since 1984 in Japan.

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