What performance ratio should a rooftop solar plant guarantee at commissioning, and how is it checked?
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
- Rooftop solar output falls each year
- Payback of rooftop solar for a factory
- Free 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, 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. Clause 18 is in the model vendor agreement, Annexure 2.