Output, not the product: a promise that the panel will still produce at least a stated percentage of its rating after a stated number of years. The physical product is covered by a separate, usually shorter, warranty, and the two are frequently confused.
Panels carry two separate promises with different lengths and different subjects, printed close together.
The product warranty
Covers defects in the panel itself — delamination, junction box failure, frame problems. It is the shorter of the two and it is the one that behaves like an ordinary warranty.
The performance warranty
Covers output over time. It states a percentage of the original rating that the panel will still reach after a given number of years, usually with a first-year allowance and an annual degradation figure after it. Those two numbers together describe the curve being promised.
What the terms actually require
Measurement under defined conditions, documentation of the installation, and often installation by an approved party. The conditions matter because a panel producing less on a hot roof is not producing less under test.
Who the promise is from
A warranty is only as durable as the entity issuing it, and this market has seen makers disappear within the term of warranties they wrote. That is not a reason to ignore the document — it is a reason to read the degradation figure, which describes the panel, alongside the years, which describe a company.
Where this page and the manufacturer’s documentation differ, the documentation is the one to follow. Every capacity, output, input window, current limit, cycle count and temperature threshold on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And for any panel rating: peak watts are measured under standard test conditions — a defined irradiance, a defined cell temperature and a defined spectrum. Those conditions exist so that two panels can be compared, not so that a yield can be predicted. This page reports the maker’s figure as a test result and derives no daily energy from it.
What people ask before they order
How would a claim be proved?
By measurement under defined conditions, which is why the terms specify how output is to be assessed. That procedure is part of the warranty document and it is the part worth reading.
Does a longer warranty mean a better panel?
It means a longer commitment from whoever issues it, which is worth exactly as much as their continued existence. The degradation figure and the product warranty tell you more about the panel.
Last reviewed 16 September 2026