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Panel degradation curve
Updated August 6, 2026 · reflecting NREL PV degradation research (~0.5%/yr median) · by Cali Energy
How long do solar panels last? Most carry 25-year warranties and keep producing well beyond. At an illustrative 0.5% per year — the median degradation rate in NREL’s research — a panel still makes about 88% of its original output after 25 years, and roughly 82% after 40. Output fades slowly; it doesn’t suddenly stop.
✓ Illustrative curve at NREL’s ~0.5%/year median degradation rate. See the figure and formula it uses ↓
A visual of how slowly output declines — not a forecast or warranty tool.
Fixed at an illustrative 0.5% per year (NREL reports a median near 0.5–0.6%, with a higher mean). Your panels’ actual rate depends on the module and site.
The rates and figures this calculator usestap to verify
The tool applies a fixed annual degradation rate to project remaining output at any year, either compounded or linear. Here is the figure and formula it uses.
| Annual rate | 0.5% / year (illustrative) |
| Basis | NREL review (Jordan & Kurtz, 2012) across ~2,000 modules; the mean is higher |
| Compounded | 100% × (1 − 0.005)^years |
| Linear | 100% − 0.5% × years |
0.5%/year is the median from NREL degradation reviews (Jordan & Kurtz, 2012 analytical review and the 2016 compendium of ~11,000 rates); the mean is higher (~0.8%) and premium modules can be lower. These are older research figures on module physics, not a fresh tariff — the rate is stable year to year. This is an illustrative curve, not a forecast or a warranty calculation; your panels’ guaranteed retained output is written in their performance warranty, commonly around 85–92% at year 25.
Example results you can reproduce
Each row reads the curve at a given year for both formulas — move the year slider above to reproduce it.
| Year | Compounded | Linear |
|---|---|---|
| 25 | 88.2% | 87.5% |
| 30 | 86.0% | 85.0% |
| 40 | 81.8% | 80.0% |
How this calculator works
It starts from 100% output and subtracts a fixed 0.5% a year. Compounded takes 0.5% off the previous year’s remaining output each year (the more realistic shape); linear takes a flat 0.5% of the original every year. Over a few decades the two barely diverge, which is the point — at these rates a panel loses only a small fraction of its output across its whole service life.
How to read your result
The big percentage is the panel’s remaining output at the year you picked, relative to when it was new. It’s an illustration of the shape of decline, not a prediction for a specific panel. Your module’s real guarantee is its performance warranty — often about 85–92% retained at year 25.
What moves the result the most
The degradation rate itself. At 0.5% a year a panel keeps ~88% after 25 years; at 0.8% (closer to the industry mean) it’s about 82%; a premium module rated near 0.25% keeps ~94%. Heat is the main real-world accelerant, which is one reason a well-ventilated, quality install ages more gracefully than a hot, cheap one.
Common questions
How long do solar panels last?
They don’t stop at a fixed age — most carry 25-year warranties and keep producing well past that at gradually reduced output. Many 30-year-old panels still make the large majority of their original power.
What does “degradation” mean?
The slow yearly decline in how much a panel produces as its materials age. It’s measured as a percent per year — around 0.5% for a typical module.
What degradation rate is realistic?
NREL’s research puts the median near 0.5% a year, with a higher mean around 0.8%. Premium modules advertise rates as low as ~0.25%. This tool uses 0.5% as an illustrative middle.
Compounded or linear — which is right?
Compounded is the more realistic shape, since each year’s loss is a slice of what’s left. Over 25–40 years the two barely differ, so either gives a fair picture of how gently output fades.
What does the warranty actually guarantee?
A performance warranty promises a minimum retained output at a given year — commonly around 85–92% at year 25. That’s a floor the manufacturer stands behind, separate from this illustrative curve.
Do panels suddenly die at 25 years?
No — 25 years is a warranty milestone, not a cliff. Panels keep working afterward at slowly declining output; the more likely reason to replace them decades on is to fit newer, higher-wattage modules.
Sources
- NREL — Photovoltaic Degradation Rates (Jordan & Kurtz)
- DOE — Solar Performance and Efficiency
- NREL — PV Field Performance and Reliability
Estimates only, not a quote. Assumptions, rates, incentives and program rules can change — confirm current details with your utility, the program administrator or a licensed professional.
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