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What evidence you need for a solar warranty or performance claim
By Dr. Andrie Udal · SolarMD · Published 29 September 2026
A warranty is only as useful as the evidence behind it. Many commercial solar owners discover that when something goes wrong: the warranty exists, but the claim stalls because the records are missing, the data is incomplete, or nobody can show the problem is the product rather than the site.
This guide explains what evidence manufacturers and contractors typically ask for, how to build it before you need it, and where an independent review fits in. It is general guidance — always check the exact terms in your own warranty documents and contracts.
Know which warranty you are claiming under
Commercial systems usually carry several separate warranties, each with its own owner and conditions:
- Module product warranty: covers defects in materials and workmanship of the panels.
- Module performance warranty: promises a minimum output over time, usually expressed as a declining percentage of rated power.
- Inverter warranty: typically shorter, sometimes extendable.
- Installer workmanship warranty: covers installation defects such as wiring, mounting and waterproofing — often the shortest.
- Contractual performance terms: some EPC, O&M or power purchase agreements include production commitments with their own measurement rules.
Getting this right matters: a claim sent to a module manufacturer for what is actually an installation fault will usually be rejected.
The core documents
- Purchase invoices and proof of installation date.
- Equipment serial numbers, datasheets and warranty certificates.
- As-built drawings and single-line diagram.
- Commissioning test records — for example string voltage and current checks, insulation resistance and polarity tests of the kind described in IEC 62446-1.
- Maintenance and cleaning logs showing the system was operated as the manufacturer requires.
Performance data that stands up
Raw kilowatt-hours are rarely enough. A low month might be caused by weather, grid outages or curtailment rather than a defect. Credible performance evidence usually includes:
- Continuous, time-stamped monitoring data at inverter level (and string level if available), with gaps explained.
- Irradiance or weather data so production can be normalised for sunlight. IEC 61724 describes widely used monitoring approaches and metrics such as performance ratio.
- A baseline — commissioning results or early-life production — to compare against.
- Exclusions documented: outages, curtailment, maintenance shutdowns and monitoring failures clearly marked.
- Comparisons between identical units: if one inverter or string under the same conditions produces clearly less than its neighbours, that is strong evidence.
Field test evidence
When data points to a component problem, manufacturers often want physical evidence. Common tests, carried out by qualified technicians, include:
- Infrared (thermal) imaging to find hotspots, failed bypass diodes and overheating connections.
- IV curve tracing to measure how strings or modules actually perform against their rated curve.
- Insulation resistance testing to find wiring or module insulation faults.
- Clear, dated photos of defects, labels and serial numbers.
Record who did the test, the equipment used, the date, and the weather conditions at the time. Tests done without that context are easy to challenge.
Why claims commonly stall
- Missing serial numbers or proof of purchase.
- No maintenance records, giving the manufacturer grounds to argue neglect.
- Monitoring gaps covering the period in question.
- Production compared to a sales estimate instead of a weather-normalised expectation.
- The original installer is no longer trading, and nobody else has the records.
- The claim is filed after the warranty period has ended.
Warranty evidence checklist
- Create one folder (digital and backed up) for all warranty certificates, invoices and serial numbers.
- Note every warranty end date in the facility calendar, with a reminder 12 months before.
- Export monitoring data regularly — do not rely only on the vendor portal.
- Keep irradiance or weather data alongside production data.
- Log every cleaning, inspection, fault and repair with date and contractor name.
- Keep commissioning and periodic test reports in the same folder.
- When a fault appears, photograph it and record conditions before anything is changed.
- Send claims in writing and keep copies of all correspondence.
When to get an independent check
Consider independent support if:
- A warranty is about to expire and you suspect a problem.
- A manufacturer or contractor has rejected a claim and you are not sure why.
- You believe the system is underperforming but cannot prove it from the data you have.
- The original installer is unavailable and records are incomplete.
SolarMD helps organise, normalise and interpret the evidence so your claim is clear and complete. We do not decide claims and cannot promise an outcome — the manufacturer or contractor makes that decision under the warranty terms. Field tests and any repairs are carried out by licensed contractors. You can see how we present findings in our sample Solar Health Score report.
Frequently asked questions
What is the difference between a product and a performance warranty?
A product warranty covers defects in materials and manufacturing. A performance warranty promises that modules will still produce a minimum percentage of their rated power after a given number of years. They are claimed differently and need different evidence.
Is monitoring data enough to prove a warranty claim?
Usually not on its own. Manufacturers typically want production normalised for weather, a baseline for comparison, documented exclusions such as outages, and often field tests such as thermal imaging or IV curve tracing by qualified technicians.
What if our installer is no longer in business?
Module and inverter warranties are normally held by the manufacturer, so they may still be claimable. Workmanship warranties are harder. Gather invoices, serial numbers and commissioning records, and consider an independent review to rebuild the evidence.
Can SolarMD file the claim for us?
We can help you prepare a clear, organised evidence pack and explain what it shows. The claim itself is made by the system owner under the warranty terms, and the decision rests with the manufacturer or contractor.
Related asset care guides
Want an independent view of your system?
SolarMD is an independent solar intelligence and lifecycle coordination service for commercial, industrial and hospital sites using around 30,000 kWh per month or more. We diagnose performance, organise the evidence and, where needed, help you find qualified EPC contractors or explore partner financing options. Repairs and engineering sign-off stay with licensed contractors.
Or email hello@solarmd.net · See a sample Solar Health Score report (PDF)
