# What performance ratio should a rooftop solar plant guarantee at commissioning, and how is it checked?

Canonical: https://senseible.earth/answers/rooftop-solar-performance-ratio-75-percent-guarantee

The Ministry of New and Renewable Energy (MNRE) model vendor agreement says the plant's performance ratio (PR) must be 75% at commissioning and be maintained for 5 years. The vendor must lend a radiation sensor with a valid calibration certificate.

## What the model agreement says

- Clause 18, Performance of Plant: the performance ratio of the plant must be 75% at the time of commissioning by the distribution company (discom) or its authorised agency.
- The vendor must provide, on a returnable basis, a radiation sensor with a valid calibration certificate of any NABL / International laboratory at the time of commissioning or testing. NABL is the National Accreditation Board for Testing and Calibration Laboratories.
- The vendor must maintain the PR of the plant till warranty of project, which the clause defines as 5 years from the date of commissioning.
- Clause 18 prints no test length and no remedy if the plant falls short. Agree both in writing.

## How performance ratio is worked out

The guideline gives the 75% figure but no formula. The usual definition, which is my reading of standard practice and not printed in the guideline, is: PR = energy the plant delivered in the month, divided by (plant size in kilowatts peak (kWp) x sunlight that fell on the module plane in kilowatt hours per square metre, divided by 1 kilowatt per square metre).

The radiation sensor supplies the second number. My reading: without a calibrated sensor you have no measured sunlight figure, so the 75% cannot be checked.

## What to write into your own contract

- The sensor make, where it is mounted (in the plane of the modules) and the calibration certificate number.
- How many days of readings make the commissioning test, and who signs the sheet.
- What the vendor does if the result is under 75%: repair, add modules or refund. The guideline is silent.
- Whether the 5 year maintenance duty includes a yearly PR check.

## Where this comes from

This is a model agreement for residential systems under the scheme, and its disclaimer says disputes are between vendor and consumer, with MNRE and the distribution utilities not a party. For a factory it is a template, not a rule that binds your installer.

## A 100 kWp plant in a 30 day month (example numbers)

- Sunlight on the modules: 5.5 kilowatt hours per square metre a day (an example, not a site figure)
- Energy at 100% PR: 100 x 5.5 x 30 = 16,500 kilowatt hours (kWh)
- At 75% PR: 16,500 x 0.75 = 12,375 kWh
- At 70% PR: 16,500 x 0.70 = 11,550 kWh, so 825 kWh a month short of the 75% figure (12,375 minus 11,550)
- Grid carbon dioxide (CO2) on those 825 kWh: 825 x 0.675 = about 557 kilograms

Only the 75% is from the guideline. Sunlight and plant size are example numbers; 0.675 kilograms of CO2 per kWh is the Central Electricity Authority (CEA) grid factor for financial year 2025-26.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records. Plant performance data from a meter or inverter can be connected as a custom integration on request; keep the commissioning test sheet with your contract.

- [Solar inverter reading or net meter for Scope 2](https://senseible.earth/answers/solar-inverter-reading-vs-net-meter-scope-2)
- [Rooftop solar output falls each year](https://senseible.earth/answers/solar-panel-degradation-and-scope-2-claim)
- [Payback of rooftop solar for a factory](https://senseible.earth/answers/rooftop-solar-payback-for-a-factory)
- [Free calculators](https://senseible.earth/calculators)

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. Clause 18 is in the model vendor agreement, Annexure 2.