Free tool
Panel degradation calculator
A performance warranty is a floor, not a promise of a number. This draws the floor and tells you whether a reading is under it.
A solar panel performance warranty guarantees a minimum output for each year of the term, falling on a published schedule: a larger drop in the first year, then a smaller drop every year after. Producing less than you did last year is normal. Producing less than the schedule guarantees is the only version that is a claim.
Off the nameplate.
Stated separately in most warranty schedules.
Per panel, at or near standard test conditions. Leave blank to just see the curve.
Guaranteed at year 8
415 W
Enter what the panel is actually producing to see whether it is above or below the floor its warranty guarantees.
At year 10
410 W
At year 25
378 W
At year 30
367 W
The first year and annual drop figures are the ones printed in your panel's own performance warranty, and they differ by manufacturer and by model. The values here are placeholders. Read them off your document before you trust the curve.
Below the line is not the same as defective
A reading under the guaranteed floor is grounds to investigate, and that is all it is. A dirty panel, partial shading from a tree that has grown, a failing optimiser and a genuinely degraded cell all produce the same disappointing number on a meter.
Clean the array, check the string, check for new shading, and measure again on a clear day near standard test conditions. A performance claim that turns out to be six months of dust is the fastest way to lose credibility with a manufacturer you will need to deal with again.
Why the y axis starts at 70 percent
The entire story of panel degradation happens between 100 percent and roughly 85 percent of nameplate over thirty years. Drawn from a zero baseline it is a flat line with a slight droop, which is honest and useless.
The chart here starts at 70 percent so the shape is legible, and every gridline is labelled with the percentage it represents so nothing is exaggerated by the crop. If you are comparing two panels, compare the numbers rather than the slopes.
Performance and product are different warranties
The performance warranty is about output falling faster than the schedule allows. The product warranty is about the panel being defective: delamination, a failed junction box, corrosion. They usually run for different lengths of time, and a panel can be outside one and inside the other.
In this catalogue that gap can be large. Silfab's performance warranty runs 30 years either way, while its product warranty is 12 years unless the install was registered within 180 days, in which case it is 25.
Claim Timer already holds these terms
One record per piece of equipment, with the serial, the nameplate photo and each brand's conditions on it. Put your next install in and the claim is built before the part fails.