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

Canonical: https://senseible.earth/answers/rooftop-solar-module-output-guarantee-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](https://senseible.earth/answers/solar-panel-degradation-and-scope-2-claim)
- [Datasheet checks before you accept modules](https://senseible.earth/answers/rooftop-solar-module-datasheet-checks)
- [Domestic content modules under PM Surya Ghar](https://senseible.earth/answers/pm-surya-ghar-domestic-content-modules)
- [Payback of rooftop solar for a factory](https://senseible.earth/answers/rooftop-solar-payback-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](https://mnre.gov.in/static/uploads/2025/08/f20f6d61628866e66b612810b49abd78.pdf), [Central Electricity Authority (CEA), CO2 Baseline Database, India grid factor for financial year 2025-26](https://cea.nic.in/cdm-co2-baseline-view?mappingId=234&lang=en)

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.