Your Solar Is Underperforming. Here’s How to Prove It — and What You Can Actually Claim

“It feels like it’s generating less” is not a claim. “Measured against 5.1 kWh/m²/day plane-of-array insolation, our 8 kW system returned a Performance Ratio of 61% across four clear-weather months against a contractual floor of 75%” is a claim.

The difference between those two sentences is the difference between an installer telling you it is the weather, and an installer sending an engineer.

Most articles about under performing solar explain the causes — soiling, shading, a failing inverter, a dead string. Useful, and widely available. What almost nobody explains is what happens next: how you establish the shortfall to an evidentiary standard, what your vendor actually owes you, and which forum can compel it.

This is that half.

Step 1 — Measure the right thing

Two numbers get used interchangeably in Indian solar and they are not equivalent. Which one your contract references determines whether you have a claim.

Capacity Utilisation Factor (CUF)

CUF = annual kWh ÷ (installed kWp × 24 × 365)

Simple, widely quoted, and weak as a claim basis. CUF takes no account of irradiance, temperature or grid availability. A vendor who guaranteed “18% CUF” and delivered 15% in a poor monsoon year has a complete weather defence, and it is a good one.

Performance Ratio (PR)

PR = actual kWh ÷ (plane-of-array insolation in kWh/m² × installed kWp)

PR normalises out the weather. It measures how much of the energy that actually arrived at your array was converted and delivered. It captures thermal losses, soiling, cabling losses, inverter conversion, mismatch and downtime — everything within your installer’s control — and strips out everything that isn’t.

Insist on a PR guarantee in your contract. If you already signed one referencing CUF, your position is weaker but not hopeless — see Step 3.

The benchmark that actually binds an Indian rooftop vendor

This is the strongest single fact in this article, and most consumers have never been told it.

Clause 18 of the PM Surya Ghar model consumer–vendor agreement provides:

“The Performance Ratio (PR) of Plant must be 75% at the time of commissioning of the project by DISCOM or its authorised agency. Vendor must provide (returnable basis) radiation sensor with valid calibration certificate of any NABL or international laboratory at the time of commissioning. Vendor must maintain the PR of the plant till warranty of project i.e. 5 years from the date of commissioning.”

If your system was installed under PM Surya Ghar, 75% PR is a contractual floor for five years, and your vendor was required to supply a calibrated radiation sensor at commissioning to establish it. A well-maintained Indian rooftop system should run in the 75–82% band. Seventy-five is the floor, not the target.

Step 2 — Do the arithmetic

Five steps, an afternoon’s work:

1. Take your installed kWp from the commissioning certificate — the DC capacity, not the inverter rating.
2. Get plane-of-array insolation for the month in kWh/m²/day, from the radiation sensor reading taken at commissioning or from a public irradiance dataset for your district.
3. Compute expected generation: kWp × insolation × days × PR. Run it twice — once at 0.75 (the contractual floor) and once at 0.82 (a well-run system).
4. Compare against actual from your inverter’s monthly log and, separately, your solar generation meter reading. If those two disagree with each other, that is itself a finding.
5. Repeat across at least three or four clear-weather months. A single bad month proves nothing. A sustained shortfall against the 0.75 line does.

A worked example. An 8 kWp system, in a month with 5.1 kWh/m²/day plane-of-array insolation over 30 days:

• At PR 0.82: 8 × 5.1 × 30 × 0.82 = 1,004 kWh
• At PR 0.75: 8 × 5.1 × 30 × 0.75 = 918 kWh
• Actual, from the inverter log: 746 kWh
• Implied PR: 746 ÷ (8 × 5.1 × 30) = 0.61

That is 172 kWh below the contractual floor in a single month, and a PR fourteen points under it. Repeated across four months, that is not weather. That is a defect, and it is documented.

Step 3 — Understand what your vendor actually owes you

Three separate obligations sit on three different parties. Consumers routinely pursue the wrong one.

The installer, under PM Surya Ghar

The model agreement is more generous than most consumers realise. Clause 12: five years of comprehensive operation and maintenance from the date of commissioning by the DISCOM, “including overhauling, wear and tear, and regular checking of healthiness of system at proper interval.” Clause 9: the complete system is warranted for five years from commissioning.

The scheme guidelines are blunter still: “Non-performing/under-performing system component will be replaced/repaired free of cost in the CMC period.”

Note also clause 10 — net meter supply, testing and DISCOM approvals are in the vendor’s scope — and clause 7, the documentation handover.

On cleaning, there is a genuine conflict worth knowing. MNRE’s guidelines put cleaning inside the comprehensive maintenance contract, and Delhi’s implementation says so explicitly. Much of the EPC industry publicly asserts cleaning is the consumer’s responsibility unless bought as an AMC. If you are under PM Surya Ghar, the CMC is comprehensive and free — get the scope written into the agreement.

The module manufacturer, under the performance warranty

Two documents, and conflating them is the most common consumer error:

MNRE’s SOP of 6 May 2026, as reported, mandates a minimum 10-year product warranty and 25-year performance warranty for modules under PM Surya Ghar and PM-KUSUM, with the warranty running from the date of installation if that is within six months of the manufacturer’s invoice — and reduced proportionately if not. That last clause exists to stop vendors installing aged stock.

Claim SLAs under the same SOP: acknowledgement in 24–48 hours, inspection within 7 days, replacement within 30 days, extendable to 90 where fresh manufacturing is required.

Critically, a performance warranty is tested at STC — 1000 W/m², 25°C cell temperature — not by rooftop kWh. Low generation on your roof is evidence that something is wrong; it is not itself proof that the modules are below their warranted curve. That requires I-V testing.

What no warranty covers

Soiling and bird droppings. Shading from a structure built after installation. Hail, lightning, storm, flood, fire. Incorrect installation or unauthorised modification. Grid overvoltage. Defaced serial numbers.

Several of those — soiling, shading, incorrect installation — point back at your installer, not the module maker. Getting the respondent right is half the battle.

Step 4 — Build the evidence file

In this order:

1. Contract documents — the vendor agreement, especially clauses 9, 12 and 18; the quoted or assured generation figure; any PR guarantee
2. Commissioning records — DISCOM commissioning certificate, project completion report, module and inverter serial numbers, layout and electrical single-line diagram, structure design drawing
3. Generation data — monthly inverter logs from year one, plus solar generation meter readings. This is the single most decisive evidence and the thing consumers most often fail to keep. Start today if you haven’t.
4. Billing data — net meter import and export registers, and bills across the disputed period
5. Irradiance reference — the calibrated radiation sensor reading from commissioning, or district-level irradiance data
6. Third-party inspection report — see below
7. Correspondence trail — dated complaints with ticket numbers

Step 5 — Get the right test

Who can do it: EL and I-V testing must be at NABL-accredited laboratories under the MNRE SOP — and not every laboratory calling itself a solar lab holds accreditation for those specific tests, so check the scope. NISE, the National Institute of Solar Energy, operates the government’s own PV testing facility. International inspection firms with Indian operations also offer on-site I-V tracing and thermography.

Who pays: under the SOP, third-party testing cost is split 50:50 between manufacturer and consumer up front, and then borne in full by whichever party is found responsible. Get that agreement in writing before testing begins.

Step 6 — Escalate

Your installer first, in writing, with a deadline. Set out the measured PR, the months covered, the clause you rely on, and what you want done. Most legitimate disputes end here once the arithmetic is on paper.

Then MNRE’s vendor complaint route if the system is under PM Surya Ghar. The SOP notified in June 2026 puts the Ministry on a defined clock — eight days for clarification, seven for a reminder, fifteen for show cause, and portal deactivation within thirty days, with the vendor named publicly. Failure to provide operation and maintenance is a listed violation.

Then the District Consumer Commission. It handles claims where the consideration paid is up to ₹50 lakh, which covers essentially every residential and most small commercial rooftop disputes. Limitation is two years from the cause of action. Filing is free where the consideration is up to ₹5 lakh. File online at e-jagriti.gov.in. The National Consumer Helpline is 1915 for free per-litigation mediation, which is not a precondition.

Plead deficiency in service expressly. That is the head under which solar under performance sits.

Is there precedent?

A little, and it is very recent. A District Consumer Disputes Redressal Commission at Vizianagaram, Andhra Pradesh, in an order reported as dated 11 June 2026, found deficiency in service against a renewable energy company where a consumer alleged the rooftop system failed to generate the assured electricity, and awarded a total of ₹25,265 with compliance within 45 days.

We are giving you the total only. Two national outlets reported different breakdowns of the same award, and we could not obtain the order text — so treat the detail as press reporting rather than settled fact.

There is no body of case law here yet. We found no NCDRC or State Commission decision on rooftop solar under performance in 2025–26. The Vizianagaram order matters precisely because it is early.

One structural limitation to plan around: under both the model agreement and the MNRE warranty SOP, disputes are strictly between consumer and vendor. MNRE and the DISCOM are expressly not parties. Your contract is the instrument that protects you.

Before you assume it’s a defect

Rule out the ordinary causes first, because they account for most cases and several are free to fix:

• Soiling. Indian field measurements put daily accumulation at 0.24–0.39% depending on season, with uncleaned annual losses measured at 14% in Delhi and 20% in Jaipur. With a weak monsoon this year, panels are dirtier than usual. Clean them, wait a week, re-measure.
• New shading. A neighbour’s water tank, a grown tree, a new floor next door. Walk the roof at 10am and 3pm.
• Inverter faults or de-rating. Check the fault log and the internal temperature. An inverter in an unventilated space throttles in May.
• A dead string. If one string is consistently more than about 20% below its neighbours, that is a fault, not a trend.
• Loose or corroded DC connectors. Testing of field-aged Indian connectors found units six years or older in harsh climates running at 300–600% of initial contact resistance against a 150% permissible limit.

If cleaning and a string check restore your numbers, you never needed a claim. That is the outcome we would rather you have.

What Solnce does about this

We run plant health checks on systems installed by anyone — most of the systems we take on were installed by someone else. You get measured PR against the 75–82% band, a defect list graded by severity and safety, an estimate of generation being lost and to what cause, what remains recoverable under warranty, and a recommended maintenance interval with the reasoning.

And if your system is healthy and your site is low-dust, we will tell you that a cleaning schedule is all you need. An AMC sold to someone who doesn’t need one is a customer lost at renewal.

Frequently asked questions

1. How do I know if my solar system is underperforming?

Compute Performance Ratio: actual kWh divided by (plane-of-array insolation in kWh/m² × installed kWp). A well-maintained Indian rooftop system should run at 75–82% annually. A sustained shortfall below 75% across several clear-weather months is evidence of a problem.

2. What Performance Ratio should my system achieve?

Under the PM Surya Ghar model agreement, 75% at commissioning, maintained for five years. A well-run system typically achieves 75–82%. Seventy-five is a contractual floor, not a target.

3. What is the difference between Performance Ratio and CUF?

CUF is annual generation divided by rated capacity times hours in the year — it ignores irradiance, temperature and grid availability entirely. PR normalises for the sunlight that actually reached your array. A CUF guarantee gives your vendor a weather defence; a PR guarantee does not.

4. How do I calculate my expected generation? 

Installed kWp × plane-of-array insolation (kWh/m²/day) × number of days × PR. Run it at 0.75 for the contractual floor and 0.82 for a well-run system, and compare both against your inverter log.

5. My generation dropped this year. Is that normal degradation?

Some decline is normal — modules typically warrant around 2% loss in year one and roughly 0.55% a year thereafter. A drop of 10–15% or more against the same months last year is not degradation, and warrants investigation.

6. What does my installer owe me under PM Surya Ghar?

Five years of comprehensive operation and maintenance from the date of DISCOM commissioning, including overhauling and wear and tear, with non-performing or under-performing components repaired or replaced free of cost. Plus a 75% Performance Ratio maintained across that period.

7. What is the difference between product warranty and performance warranty? 

Product warranty — typically 10 to 12 years on Indian modules — covers defects in materials and workmanship. Performance warranty — typically 25 years — guarantees measured output at standard test conditions stays above a defined curve. They are separate documents with separate remedies.

8. Does low generation on my roof prove a warranty breach?

No, and this catches people out. Performance warranties are tested at standard test conditions — 1000 W/m² and 25°C cell temperature — not by rooftop kWh. Low rooftop generation is evidence that something is wrong; proving the modules are below their warranted curve requires I-V testing.

9. What testing do I need for a warranty claim?

I-V curve tracing to measure actual power against STC-corrected nameplate, and electroluminescence imaging to reveal microcracks and cell damage. Both are mandatory under MNRE’s May 2026 SOP and must be done at NABL-accredited laboratories. Infrared thermography is a useful, faster first screen.

10. Who pays for third-party testing?

Under the MNRE SOP, the cost is split 50:50 between manufacturer and consumer up front, then borne in full by whichever party is found responsible after testing. Agree this in writing before testing begins.

11. What are the warranty claim timelines? 

Per the SOP as reported: acknowledgement within 24–48 hours, inspection within 7 days, and module replacement within 30 days — extendable to 90 days where fresh manufacturing is required.

12. What isn’t covered by a solar warranty? 

Soiling and bird droppings, shading from structures built after installation, hail, lightning, storm, flood and fire, incorrect installation or unauthorized modification, grid over voltage, and defaced serial numbers. Note that soiling, shading and incorrect installation point back at your installer rather than the module manufacturer.

13. Can I take my solar company to consumer court?

Yes. The District Consumer Commission handles claims where the consideration paid is up to ₹50 lakh, which covers essentially every residential rooftop dispute. Limitation is two years. Filing is free where the consideration is up to ₹5 lakh. Plead deficiency in service expressly.

14. Has any Indian consumer court ruled on solar under performance?

A District Commission at Vizianagaram, Andhra Pradesh, in an order reported as dated 11 June 2026, found deficiency in service and awarded a total of ₹25,265 with compliance in 45 days. There is no wider body of case law yet — we found no NCDRC or State Commission decision on the point in 2025–26.

15. Can I make MNRE or my DISCOM a party to a warranty dispute? 

No. Both the model agreement and the warranty SOP place disputes strictly between consumer and vendor. MNRE and the DISCOM are expressly not parties, which is why your written contract matters so much.

16. What records should I keep from day one? 

Monthly inverter generation logs, solar meter readings, the commissioning certificate, module and inverter serial numbers, warranty certificates, the layout and single-line diagram, and every complaint with its ticket number. Generation logs are the most decisive evidence and the most commonly missing.

17. Could dirty panels explain my drop? 

Very possibly. Indian field studies measure daily soiling accumulation at 0.24–0.39% by season, with uncleaned annual losses of 14% in Delhi and 20% in Jaipur. With below-normal rainfall this year, panels are dirtier than usual. Clean, wait a week, re-measure before concluding anything.

18. What if my installer has closed down? 

Your module and inverter performance warranties are with the manufacturers and survive your installer. You will need the serial numbers and warranty certificates from your commissioning file — which is why insisting on that handover at installation matters. Any competent O&M provider can perform the diagnostics and support the claim.

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