Product warranty versus performance warranty

In short: A solar module carries two warranties with different jobs. The product warranty covers defects in materials and workmanship; the performance warranty promises how much rated power the module keeps, year by year, measured in a lab. Across our catalogue the median product warranty is 15 years against 30 years for performance, and on 89 % of modules stating both, the product warranty is the shorter one.

The datasheet prints the two lengths side by side, as if they were two versions of one promise. They aren't. They cover different failures, and they can end in different years.

Two promises with different jobs

The product warranty pays out when something breaks. A junction box that fails, a connector that corrodes, a cell that was faulty from the factory: these are defects, and only the product warranty names them.

The performance warranty doesn't care why power is missing. It's a schedule: so much of the rated power after year one, a little less each year after that. If a module measured in a lab falls below its line, the manufacturer owes you a remedy.

The drawing below shows the split. Its 10 and 25 years are an older pairing, so take today's lengths from the tables further down; the logic is the same. Early and mid-life faults fall inside the product warranty, slow wear is tracked against the performance line.

What I counted and what I read

Of the 14,005 modules in the catalogue, 13,615 state a product warranty, 13,877 a performance warranty and 12,330 the power the performance warranty promises at its end. One datasheet usually covers a ladder of power ratings, the same module sold at several wattages, and each rating is its own row here. The sanity ranges and the count behind every figure are under "Figures and denominators" below the article.

I group by cell technology and by manufacturer, two things the datasheets state themselves. I left out manufacturer tier: our "Tier 1" flag was filled in by a language model, not taken from a published list, so nobody could check a finding resting on it.

What each warranty covers is in the manufacturer's warranty document, not the datasheet. I read two from LONGi: its March 2024 limited warranty for Hi-MO X6 modules in the distributed generation (rooftop) market, and an older one for its single glass modules, both from copies on Australian solar websites. Other manufacturers write their own terms, so read the clauses below as one worked example.

Two modules run through the article, picked by rule when it was written; nobody paid for either place. The first had the most shop offers in our live offers list among modules whose warranty figures agree with each other (the end figure follows from the degradation figures; the datasheet article explains that check). It's a LONGi module.

The second had the most shop offers among modules with a product warranty of 25 years or more. It's a Jolywood module.

How long each warranty runs

Product warranty lengths

Look for three lengths in the chart: 12 years, stated by 44 % of modules, 15 years by 30 %, and 25 years or more by 21 %.

Performance warranty and how the two pair up

Of the modules stating a performance warranty, 70 % promise 30 years or more. The table counts modules for eight common pairs. Compare the rows where the two lengths match with those where they don't, to see how much one length tells you about the other.

The length and the power promised at the end are separate terms, so read both. The median module with a 25-year performance warranty is promised 84.8 % of its rated power when it ends. The median module with a 30-year warranty is promised 87.4 %, five years later.

The modules with the longest stated performance warranty, picked by the rule in the caption:

Top 3 by the longest performance warranty, one module per datasheet, among 13,877 modules with a stated performance warranty, as of the last catalogue sync.

Warranties by cell technology

The product side first. "N-type only" means the datasheet says N-type without naming the cell structure; back contact cells have all their contacts on the rear face.

On the performance side, the end power is the median promised when the warranty ends, whatever its length.

Read the two columns together. A 25-year schedule stops five years before a 30-year one, so where two groups differ a lot in the first column, their end figures aren't taken at the same year. Within one length, the end figure follows from the degradation allowances: a smaller first-year loss and a lower annual rate leave more power.

Warranties by manufacturer

Counting companies rather than modules, 66 manufacturers have a median product warranty of 12 years, 52 of 15 years and 37 of 25 years or more.

108 manufacturers state more than one product warranty length across their own modules, so for them the brand doesn't settle the term. LONGi's 2024 rooftop warranty shows how that happens: one document gives 25 years of product warranty to some module types and 15 years to others, listed by model number. The older single glass warranty gave 10.

Among manufacturers that list both TOPCon and PERC modules, 26 give TOPCon the longer median product warranty, 50 give both the same and 12 give TOPCon the shorter one. Which manufacturers state the longest terms, with a minimum number of datasheets behind each, is in warranty terms across manufacturers.

What each warranty covers

Product warranty: defects in materials and workmanship

LONGi's 2024 document draws the line plainly. It says the modules, "including the DC connectors and cables", will be free of defects in material or workmanship which affect the performance of the modules, provided they're installed and maintained as the installation manual says. It excludes changes in appearance and normal wear and tear, and says outright that power output isn't covered here.

A defective cell is the kind of fault this warranty exists for. It often shows up as a hot spot, a cell running hotter than its neighbours, which an infrared camera picks up even when the module looks fine. Whether a fault qualifies is decided under the document, so a clear record helps.

Performance warranty: a power schedule measured in a lab

For one group of modules, LONGi promises at least 99 % of rated power in the first year and a decline of no more than 0.35 % a year after that: 99 - 0.35 × 29 = 88.85 % in year 30.

Power is measured at standard test conditions (1000 W/m², 25 °C cell temperature) in an independent lab the supplier accepts, with the equipment's measurement tolerance taken into account. That isn't what a module makes on your roof on a hot afternoon, and the warranty never says it is.

Three clauses that matter more than the length

The remedy is the supplier's choice. It can repair the modules, replace them, add modules to make up the shortfall, or refund either the module's residual value or the value of the missing power. Residual value is the current price per watt times the rated power times the share of the performance warranty period that's left.

Labour is yours. Dismantling, repacking and reinstalling the modules fall on the customer.

The clock doesn't restart. A repaired or replaced module carries the remainder of the old warranty.

The two examples, worked through

The LONGi module states 15 years of product warranty and 30 years of performance: 1 % allowed in the first year and 0.35 % a year after, so 100 - 1 - 0.35 × 29 = 88.85 % at year 30. The Jolywood module states 25 years of product warranty and the same 30 years of performance, at 1 % and 0.4 % a year: 100 - 1 - 0.4 × 29 = 87.4 %.

So the two trade in opposite directions. Year 20 sits inside both performance warranties; look at the last column.

The LONGi module promises slightly more power. Only the Jolywood module is still covered if a junction box fails that year. Which matters more depends on what you fear: slow fade, or a part that breaks.

The figure below runs both schedules year by year, with bars for the warranty still running. The second module starts on the Jolywood terms; you can change either.

Checklist before you buy

1. Read the product warranty first. It's the one that names defects: a failed connector, a cable, a fault in the module's materials.
2. Compare the schedule, not the headline. "30 years" on two datasheets can mean different end figures, so work out the guaranteed power in the year you care about from the first-year allowance and the annual rate, for both modules.
3. Ask for the warranty document. The remedy, the claim procedure and who pays for labour are only there. Under the LONGi terms, a residual value refund in year 20 of a 30-year warranty is 10 / 30 = a third of what the module's watts cost that day, and the labour is yours.
4. Check the model number. A warranty you read for one series doesn't carry over to another line from the same manufacturer.

The panel comparison calculator shows the warranty fields of any two catalogue modules side by side. The payback calculator shows how many years a system needs to pay for itself, and that's the stretch I'd read any warranty against.

What these figures can't tell you

Every length here is our reading of a datasheet, a claim on paper. The datasheet can differ from the current warranty document, and the document is what binds. The clauses are one manufacturer's terms, in one market, at one date. And a warranty is only as good as the company that has to honour it, which no datasheet field measures.

Module shares count rows, so a manufacturer with long power ladders weighs more in them than one with short ladders. That's why the manufacturer figures count each company once.

The performance warranty doesn't cover output lost to heat, shade, soiling or a poorly matched inverter, and its first-year allowance absorbs early losses such as light-induced degradation. None of these figures measures how cells actually age.