Maintenance & lifespan

Panel degradation calculator

Enter your panel wattage, technology type, first year light induced degradation, and annual degradation rate. See exact output at any year up to 30.

Your panel details

1 Project details Optional
Shown on your exported report. Leave blank to skip.
2 Your panels
Rated STC output printed on the panel datasheet.
Used to show total array output, not just per panel.
Sets a default annual degradation rate. Overridable below.
Leave blank to calculate from a brand new install.
3 Degradation rates
One time drop from light induced degradation, separate from the annual rate. Datasheets list this as 1% to 3% typically.
Steady yearly decline after year one. Overrides the panel type default if filled in.
How many years from install to project forward. Most warranties run to year 25 or 30.
From your panel's performance warranty. Leave blank to skip the comparison.

How it works

Three steps to your degradation number

Step 1

Find your panel's degradation rate

Check your panel's datasheet for a first year LID figure and an annual linear degradation rate. If you can't find yours, pick your panel technology above and we'll use a typical published rate. The degradation by brand tool lists rates for common manufacturers.

Step 2

Pick a projection year

Most warranties guarantee output through year 25 or 30. Enter that year, or check multiple years by re-running the calculator, to see how the curve looks at year 10 versus year 25.

Step 3

Compare against the warranty floor

If your panel's warranty guarantees a minimum output percentage at year 25, enter it to see your margin. Panels tracking below their guaranteed floor may qualify for a manufacturer claim under the warranty coverage value calculator.

Understanding panel degradation

Why output drops even without any damage

Solar cells lose a small amount of output every year through normal exposure to UV light, heat cycling, and moisture, even on a system with zero mechanical problems. A typical panel loses roughly 0.5% of its rated output annually after an initial first-year dip, which means a 400 watt panel still produces around 348 watts after 25 years under standard test conditions. This is expected behavior, not a defect, and every manufacturer's datasheet lists it as a guaranteed performance curve.

The difference between LID and annual degradation

Light induced degradation happens once, in a panel's first weeks of real sun exposure, and typically knocks off 1% to 3% of rated output permanently. After that one time drop, the panel settles into a steady, much smaller annual decline. Treating LID and the annual rate as the same number understates real year-one output and overstates year-25 output, which is why this panel lifespan estimator and this calculator both separate the two. For the underlying testing methodology behind these degradation ratings, UL's photovoltaic module safety standard lays out how manufacturers arrive at these figures.

How panel technology changes the curve

Standard polycrystalline panels commonly degrade 0.6% to 0.8% a year, while premium N-type and HJT panels often run under 0.4% a year. Over a 25 year system life, that gap compounds into a meaningful difference in total lifetime energy production, even if the two panels started at the same wattage. The degradation rate comparison by brand tool breaks this down by manufacturer and cell type, and the 25 year output projection tool converts that gap into actual kWh over time.

What this means for your maintenance budget

Because output declines predictably, most installers and lenders build gradual degradation into 25 year production estimates from day one. If your system is producing noticeably less than this calculator projects for its current age, that's a signal to check for soiling, shading, or a hardware fault rather than assume normal aging. Run the cleaning ROI tool first, since dirt and pollen buildup often masquerades as degradation. For practical guidance on keeping a system performing well over time, the Department of Energy's guide to operating and maintaining a PV system is worth reading.

Where degradation fits into your bigger cost picture

Lower output over time means slightly smaller annual savings, which is worth factoring into any long-range budget. Take your year-25 output figure to the 25 year maintenance cost projection to see the full picture of what your system costs and produces across its working life. If you're weighing whether a panel with a stronger degradation profile is worth a higher price up front, the loan APR impact calculator can help you see the financing side of that tradeoff.

Questions

Frequently asked

Most standard panels degrade about 0.5% a year after a one time first year dip of 1% to 2%. A 400 watt panel rated at 0.5% annual degradation still produces about 348 watts, 87% of its original rating, after 25 years.

Light induced degradation, or LID, is a one time output drop of 1% to 3% that happens in a panel's first weeks of sun exposure, separate from the steady annual decline that follows. Manufacturer datasheets list it as a distinct figure from the yearly rate.

No. Standard polycrystalline and monocrystalline panels typically degrade 0.5% to 0.8% a year, while premium monocrystalline PERC and N-type panels often run 0.3% to 0.45% a year. Over 25 years that difference can mean 4 to 6 percentage points of extra output.

Yes. Most manufacturers guarantee a minimum output percentage at year 25, commonly 84% to 87.4%, and will repair or replace panels that fall below that line. Check your specific panel's performance warranty, since guaranteed floors vary by brand and product line.

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