Most new solar panels will retain 80% of their output after 30 years
Sandia National Laboratories has completed a five-year study of solar module degradation in the first few years of service life, examining 834 field PV modules representing 13 types from seven manufacturers in three climates.
The report, published in Progress in Photovoltaics, studied 23 systems in total. Six of those studied were found to have degradation rates that will exceed panel warranty limits in the future, while 13 systems demonstrated the ability to extend their lifetime beyond 30 years. “Useful life” in this study is defined as the amount of time a panel produces electricity above 80% of its lifetime start rate.
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The report noted that module costs have fallen 85% since 2010 due to economies of scale, increased efficiency in cell design, automation of production lines, larger modules, and changes in BOM components such as backsheets. He cautioned that while decreasing costs have made solar a central part of building energy infrastructure, changes in design and materials to reduce costs could lead to a lower degradation rate, which in turn could negate many of the positive results of lower module costs.
The degradation study revealed that degradation is very nonlinear over time and that there are seasonal variations in some module types. The mean and median degradation rate values of -0.62%/year and -0.58%/year, respectively, are consistent with the rates measured for older modules.
The report says that the market share of cell types has changed dramatically in recent years. In 2018, conventional aluminum back surface field (Al-BSF) designs dominated global solar cell production, accounting for up to 90%. By 2020, the market share changed to only 15% for AI-BSF and 80% for high-efficiency cell concepts, such as passivated emitter and back-cell (PERC), passivated emitter with locally diffused back-cell (PERL), fully diffused passivated emitter back-cell (PERT), silicon heterojunction (SHJ), and tunnel oxide passivated contact (TOPCon). According to the report, long-term field data on these new cell and module technologies are lacking.
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This study sought to fill that data gap by studying each of these technologies in the field over time. It included 55% of the 2020 market in terms of number of companies represented.
Nominal power differences ranged from -3.6% to 4%, and initial power stabilization ranged from -3.3% to +0.6%. Flash-over-flash measurements showed variable performance and seasonality amplified the variations.
Overall, the degradation rates found in the work were within the values observed in the past from 1979 to 2014 in module technologies for the most expensive conventional PV technologies. The conclusion is that, although costs were drastically reduced in the last decade, module degradation rates do not seem to be affected, at least for the sample investigated in the report.
