The Study Behind the 0.75% Figure
NREL’s PV Fleet Performance Data Initiative launched in 2019 as a $5.25 million project funded by DOE’s Solar Energy Technologies Office. Analyzing roughly 2,200 solar installations, about 10% of all non-residential US PV systems, and nearly 19,000 inverters, using data collected from 2019 onward over three years, the initiative’s finding was published on June 27, 2023: a median performance loss of 0.75% a year. This is a 2023-published finding drawn from 2019-2022 data, worth stating plainly since a degradation figure this specific is only as current as the fleet it measured.
What 0.75% a Year Does to a System’s Output
Run flat and non-compounding, a straightforward illustrative estimate rather than a NREL-stated 25-year total, since real-world degradation is not perfectly linear year to year, a 0.75% annual loss would leave a system producing roughly 81% of its original output by year 25. Set that next to the industry-standard performance warranty, which typically guarantees 85% to 87% of nameplate output at year 25 according to SolarReviews’ warranty guide, and there is a real, worth-naming gap: the median observed degradation trend, extended in a straight line, runs somewhat below the floor most manufacturer warranties promise. That does not mean warranties are being broken, since actual degradation curves are not linear and vary by installation, but it is a legitimate reason to treat 0.75% as the more useful planning number than an unsourced, lower assumption.
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Book a Solar CallA 2024 Update, Split by Climate, Not Independently Confirmed
A reported 2024 NREL finding splits degradation by climate zone: 0.88% a year in hot climates against 0.48% a year in cool ones, drawn from an expanded dataset of roughly 7.2 gigawatts across about 1,700 sites and nearly 19,000 inverters, close to 6% to 7% of the entire US PV market. NREL’s own page for this specific finding was not reachable this cycle, nrel.gov was unreachable domain-wide, so this figure comes from a search result summary citing NREL, not from a page this research directly read. It is presented here as reported, not confirmed, and should be treated that way in any downstream use.
The Best Case: N-Type Cells
Per Clean Energy Reviews’ coverage of the most efficient solar panels on the market, high-efficiency N-type solar cells show light-induced degradation as low as 0.25% a year, a meaningfully lower figure than the 0.75% fleet median, and many N-type panels carry a 25 to 30 year performance warranty guaranteeing 90% or more of original rated output across that span. That is a different, narrower metric than whole-system degradation, specific to the cell technology rather than the full installed system, but it marks the low end of what current panel technology can achieve against the fleet-wide median above.
Why Degradation Rate Matters Beyond a Spec Sheet Number
A degradation rate is not just an abstract efficiency figure, it is one half of the math behind when an aging system becomes a real conversation again. This site’s own coverage of the inverter warranty gap covers the other half: a standard string inverter’s 10 to 12 year warranty runs out well before a panel’s 25-year span does, meaning inverter replacement, not panel degradation, is usually the first cost an aging system actually forces. Panel output loss compounds on top of that, which is exactly why a system in roughly its second decade of service is worth the closer look this site’s repowering candidates guide walks through.
The Numbers
NREL’s PV Fleet Performance Data Initiative found a median annual solar panel performance loss of 0.75%, based on roughly 2,200 installations and nearly 19,000 inverters analyzed from 2019 onward, published June 27, 2023.
The PV Fleet Performance Data Initiative launched in 2019 as a $5.25 million project led by NREL with funding from DOE’s Solar Energy Technologies Office.
A reported 2024 NREL update found degradation splitting by climate, 0.88% a year in hot zones against 0.48% a year in cool zones, drawn from an expanded dataset of about 7.2 gigawatts across roughly 1,700 sites. Reported, not independently confirmed this cycle.
High-efficiency N-type solar cells show light-induced degradation as low as 0.25% a year, with many N-type panels warrantied to guarantee 90% or more of original rated output across 25 to 30 years.
Industry-standard solar performance warranties typically guarantee roughly 85% to 87% of nameplate output at year 25.
Sources
The external data in this article draws on the sources below. Figures described in the text as estimates or industry triangulations are directional and are not attributed to a single dataset.
- DOE, on NREL’s PV Fleet Performance Data Initiative and its 0.75%-a-year median finding
- NREL, 2024 update on extreme weather and system aging across the US photovoltaic fleet, unverified by direct fetch this cycle
- Clean Energy Reviews, most efficient solar panels, on N-type cell light-induced degradation
- SolarReviews, guide to solar panel warranties, on the industry-standard performance warranty floor