Solar Module Degradation Warranty: What a 25-Year Guarantee Actually Promises

A 25-year module warranty is two separate promises. The product warranty covers manufacturing defects, typically for 10 to 12 years. The linear performance warranty guarantees a minimum power at year 25, usually somewhere between 80% and 87% of nameplate. You can claim only when a test shows a module below its warranted line, so the paper is worth what the manufacturer's survival and your contract make it worth.

What are the two warranties, and what does each cover?

Datasheets bundle them under one "25-year warranty" headline. Read them apart, because the remedy, the evidence and the term differ.

The last row is where owners are surprised. Many warranties cover the module itself and say nothing, or something unhelpful, about the labour, crane time or shutdown needed to swap it. Ask for that in writing before you sign.

How is the degradation curve written?

A performance warranty has a first-year drop, an annual decline after that, and a floor at the end. Datasheets state them as percentages of nameplate. Here is how to read one, using an illustrative curve (not any named manufacturer's): a first-year loss of 1.0% and a linear loss of 0.4% a year after that. Year 25 would be 100 - 1.0 - (24 x 0.4) = 89.4% of nameplate. A different datasheet that promises only 80% at year 25 is permitting a much steeper decline, and the gap between the two is real energy over the life of the plant.

Three details change the value of the number:

• Linear or stepped. A linear guarantee falls a little each year. A stepped one allows a larger drop in early years and tightens later. Ask for the year-by-year table.
• Tolerance. Nameplate power carries a manufacturing tolerance, and test equipment carries an uncertainty. A claim usually has to show the module below the warranted value after both are allowed for.
• STC, not your roof. The guarantee is about module power under laboratory conditions. It makes no promise about your plant's units. Soiling, temperature, shading and inverter clipping sit outside it. Our note on why yield estimates differ covers those.

Cell technology matters here. N-type TOPCon modules are generally sold with a smaller first-year loss and a flatter annual decline than older PERC; the datasheet is the only proof. We cover this in TOPCon and N-type modules: what changed.

How does a warranty claim work in practice?

Trade press reported in May 2026 that MNRE had issued a warranty standard operating procedure for modules supplied to its distributed schemes, PM Surya Ghar and PM KUSUM among them. The reports describe a 10-year product warranty, a 25-year power warranty, EL and I-V testing, accredited laboratories, response timelines, and a warranty clock that starts at installation if the module is installed within six months of the invoice. We could not retrieve the MNRE memorandum itself, and it governs those schemes, not a private factory contract. Use it as a checklist for what to ask your supplier to put in writing, not as a legal guarantee.

In any claim, expect to supply:

1. The purchase invoice, serial numbers and the commissioning certificate that fixes the start date.
2. A site record showing the module was installed and cleaned as the maker's manual requires.
3. A test: I-V curve tracing on site or at a laboratory, plus EL imaging where cracking is suspected.
4. An agreement on who pays for a disputed test. Some procedures split it and let the loser bear it in the end; yours should say.

Manufacturers decline claims for damage they can attribute to the installation or the site: shading hot spots, mechanical damage from walking on modules, voltage surges, wrong cleaning chemicals, broken glass from external impact. A workmanship record and a cleaning log protect your claim as much as the datasheet does.

Is the manufacturer still there in year 15?

This is the bankability question, and the warranty is only a claim on a company. Check:

• Balance sheet and track record, not only brand recall. Ask for audited accounts and the age of the module line.
• A local entity in India that can receive a claim and ship a replacement, and a named contact in the contract.
• Insurance backing or a surety for the warranty, where the maker offers it.
• Transferability if the building or the plant is sold or leased.
• ALMM status. The Approved List of Models and Manufacturers is a regulatory eligibility list. MNRE's O.M. of 4 August 2026 says List-I (modules) still applies to net-metering and open-access projects, and that neither list applies to behind-the-meter plants used solely for captive consumption by a consumer other than a government entity or public sector enterprise. Being on the list says the model is eligible. It says nothing about the maker's finances. See the O.M. and our bankability note.

What should the solar contract say?

Whoever supplies the plant should pass the manufacturer's warranty through to you and stay accountable for the claim process during their own workmanship period. Write these points into the EPC contract:

• The full warranty document of the exact module model, attached as a schedule, with the year-by-year power table.
• The warranty start date, defined as the commissioning date, with a long-stop if modules sit in a store before installation.
• Who raises and chases a claim in the first years, and who bears removal, refitting and transport.
• A sample of modules retained or tested at handover so there is a baseline, and a record of serial numbers against rows.
• The EPC contractor's own workmanship warranty, stated separately from the module warranty and from the inverter warranty.

How Secured Engineers helps

We specify modules by model, state the warranted curve and ALMM status in each proposal, and design the plant in-house. The CEIG and DISCOM net-metering filings are done by our own team, and we can run solar and the rest of the MEPF scope under one contract. We work from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients. We do not sell audits; if you already have a plant and a module question, we review the warranty documents and the plant's records and advise on the claim route.

Send us the datasheets you have been offered and we will lay the curves side by side. Read about solar PV modules and our solar EPC service, message us on WhatsApp, call +91 70099 85817, or ask for a free proposal.