What yearly output guarantee should rooftop solar modules carry over 25 years?

The Ministry of New and Renewable Energy (MNRE) specification says modules should give more than 97% of nominal power in the first year, more than 90% in the first 10 years and more than 80% in the next 15, with degradation below 0.5% a year. The defect warranty runs not less than 5 years.

The three output floors

These are clauses from the technical specification in Annexure 3 of MNRE's guidelines for its residential rooftop solar scheme, Pradhan Mantri Surya Ghar: Muft Bijli Yojana. A factory is not bound by them, but they are a published checklist to hold a quotation against.

• Clause 1.9: all photovoltaic (PV) modules should have a nominal power output of >90% at standard test conditions (STC) during the first 10 years, and >80% during the next 15 years.
• The same clause: module shall have nominal power output of >97% during the first year of installation, with degradation of the module below 0.5% per annum.
• My reading: together these make a 25 year output guarantee. STC means a lab test condition, not a roof in May, so a working plant will read lower than nameplate on a hot day.

The two figures do not say the same thing

My reading: clause 1.9's own first-year floor is more than 97%, so start there. A straight 0.5% loss a year from 97% gives 92.5% at year 10 (97 minus 9 x 0.5) and 85.0% at year 25 (97 minus 24 x 0.5). The printed floors of 90% and 80% are looser than that, since going from 97% down to 80% over 24 years allows about 0.7% a year on the same straight line. The clause does not say which test governs a claim, so ask the maker which one the warranty certificate uses, in writing.

The defect warranty is separate

• Clause 1.10: the manufacturer should warrant the modules to be free from defects and failures for a period not less than five (5) years from the date of commissioning.
• It covers defects from manufacturing, quality of materials, and non-conformity to specifications due to faulty manufacturing or inspection.
• If a module fails, the manufacturer will repair or replace it, at the Owner's sole option, and replacement is without charging any cost to the end consumer during the warranty period.

What it means for your carbon figures

Claim only the generation you read from the meter or inverter. A module that sits at the 80% floor in year 20 still counts, but your Scope 2 will rise as grid units replace the missing solar units.

What the floors cost in grid units (example plant)

• Plant: 100 kilowatts peak (kWp), example yield 1,400 kilowatt hours (kWh) per kWp a year
• Output at full nameplate: 100 x 1,400 = 140,000 kWh
• At the 90% floor: 140,000 x 0.90 = 126,000 kWh, so 14,000 kWh come from the grid instead
• At the 80% floor: 140,000 x 0.80 = 112,000 kWh, so 28,000 kWh come from the grid instead
• Grid carbon dioxide (CO2) at 0.675 kilograms per kWh: 14,000 x 0.675 = 9,450 kilograms and 28,000 x 0.675 = 18,900 kilograms

Yield and plant size are example numbers. The floors are MNRE's. The 0.675 is the Central Electricity Authority (CEA) grid factor for financial year 2025-26.

What Senseible does here

Senseible reads electricity bills into monthly records, so the units you import month by month sit in one place. It does not test module output; the generation log from your inverter or meter is the evidence, and a custom meter integration is available on request.

• Output falls every year: Scope 2 claim
• Datasheet checks before you accept modules
• Domestic content modules under PM Surya Ghar
• Payback of rooftop solar for a factory

Sources: Ministry of New and Renewable Energy (MNRE), Guidelines for PM-Surya Ghar: Muft Bijli Yojana, Central Financial Assistance to Residential Consumers, with Annexures 2 to 4, Central Electricity Authority (CEA), CO2 Baseline Database, India grid factor for financial year 2025-26

Last reviewed 2026-11-06. Re-check clause numbers and figures against the current version of the guidelines before you rely on them. Ask the module maker for its own warranty certificate; it may be stricter than this floor.