Solar panels don't fail suddenly — they fade. Every year a panel produces slightly less than the year before, a slow decline called degradation. It's gentle, predictable, and built into every manufacturer's warranty, but it does add up over decades. This calculator shows exactly how your system's output tapers over its life, and how much total energy it delivers along the way.
What causes degradation?
Panels degrade from years of exposure to sunlight, heat, humidity, and thermal cycling. The materials slowly age: the cells lose a fraction of their efficiency, and connections and encapsulation weather over time. It's normal and unavoidable — the goal is simply to use good panels with a low degradation rate so the decline stays slow.
What's a typical degradation rate?
Most modern panels degrade about 0.5% per year. Premium panels can be as low as 0.25%, while budget or older panels may be 0.7% or more. Manufacturers usually guarantee at least 80–87% of the original output at 25 years. At 0.5% per year, panels keep about 88% of their output after 25 years — still producing the large majority of their original power.
How the math works
Degradation compounds, just like interest. Each year's output is the previous year's multiplied by (1 − rate). So at 0.5%, year 2 is 99.5% of year 1, year 3 is 99.5% of year 2, and so on. Over 25 years this compounding leaves you at roughly 88%, not 87.5% (25 × 0.5%), because each year's loss is calculated on a slightly smaller base.
Why 25 years isn't the end
The 25-year figure everyone quotes is the warranty period, not the panel's lifespan. Panels keep working well beyond 25 years, just at a gradually lower output. Many systems from the 1990s are still generating usefully today. For more on what to expect long-term, see our guide on how long solar panels last.
Related tools
To find your year-1 production figure, use the energy production calculator. To see the environmental payoff of all that energy, the CO₂ emissions calculator converts it into carbon saved, and the ROI calculator shows the financial return over the same lifetime.
Frequently asked questions
How much do solar panels degrade each year?
About 0.5% per year for most modern panels. Premium panels can be ~0.25%, budget/older ones ~0.7%+. Manufacturers typically guarantee at least 80–87% output at 25 years.
How much output will my panels lose after 25 years?
At 0.5%/year they keep ~88%; at 0.7% ~84%; at a premium 0.25% ~94%. Even after 25 years, good panels still produce most of their original power.
Do solar panels stop working after 25 years?
No — 25 years is the warranty period, not the end of life. Panels keep producing beyond that, just at a reduced output.