Sourcing Solar Panels for Large Projects: 10 Red Flags in Vendor Evaluation

When you buy solar panels for a large-scale project, vendor selection isn’t just procurement — it’s risk management. One bad choice can cost months of delays, warranty headaches, reduced energy yield, and real financial loss. Below are 10 red flags to watch for when evaluating a solar panel manufacturer or supplier — each explained with why it matters and what to do instead. I source best practices and reliability research from industry authorities so you can make bankable, field-proven decisions.

Why these red flags matte

Large projects need panels that perform to spec for 20–25+ years. Independent qualification testing (IEC standards), lab scorecards, and bankability reviews reduce the probability of failure modes like LID, PID, LeTID, EVA yellowing, or mechanical failure. Independent labs and certification bodies also represent the due diligence financiers and insurers demand.

The 10 red flags — explained and actionable

1) Missing or weak certifications (IEC / IS / UL / ALMM compliance)

Why it’s a red flag: Certifications (IEC 61215 / IEC 61730 / UL where applicable) prove a model passed design-qualification and safety testing. For projects in India, inclusion on MNRE’s ALMM (Approved List of Models and Manufacturers) matters for tenders and incentives. Lack of recognized certificates or government listing signals higher risk.
What to ask for: Certificates, test reports, and the exact model numbers that were tested. Verify documents with the issuing lab or the regulator.

2) No independent reliability or bankability testing (PVEL / DNV / TÜV reports)

Why it’s a red flag: Third-party labs run long-duration tests (PID, thermal cycling, humidity freeze, power degradation). Vendors can cherry-pick internal QA data — only independent labs reveal systemic reliability issues. Scorecards from PVEL, DNV, or TÜV expose underperforming models.
What to ask for: Recent independent test reports, scorecards, and any remediations if tests show issues. Consider buying from suppliers with positive independent scorecards.

3) Warranty terms that are vague, conditional, or hard to claim

Why it’s a red flag: A 25-year linear performance warranty on paper means little if the claim process is opaque, requires excessive proof, or the manufacturer lacks the cashline to honor claims.
What to ask for: Clear warranty claim flow, contact points, sample claim resolution timeline, financial guaranty or insurance backing (e.g., bank guarantee, warranty insurance). Make warranty triggers and remedies contractually enforceable.

4) Unstable production footprint & no traceability (lot / serial / BOM)

Why it’s a red flag: Frequent product changes, multiple factories without traceability, or no lot tracking increase the chance of mixed batches and hidden defects. Traceability matters for recalls and targeted replacements.
What to ask for: Batch/serial tracking processes, BOM records (glass, cells, EVA, backsheet), and factory audits. Require traceability clauses in contracts.

5) Opaque component sourcing (cells, glass, EVA — cheap inputs hide behind a brand)

Why it’s a red flag: The module’s weakest part usually determines field life. If a manufacturer won’t disclose cell type (dopant, PERC/TOPCon/HJT), glass spec, or EVA/backsheet brands — you can’t judge durability.
What to ask for: Cell type and vendor, glass spec (tempered, anti-reflective coating), EVA supplier and formulation, and whether frames are anodized/aluminum grade.

6) Inconsistent electrical data — missing or dubious PAN / IV curve files

Why it’s a red flag: Accurate PAN files and IV curve data drive yield modelling and bankability. If the vendor sends inconsistent IV curves, or refuses to provide PAN files per serial number, simulation and O&M forecasting become guesswork.
What to ask for: PAN files (one per module type), sample IV curves at STC and temperature coefficients. Require PAN-file verification before acceptance.

7) Poor or no sample testing — or refusal to allow independent sampling

Why it’s a red flag: Vendors sometimes refuse independent sample tests or delay sending representative samples. A vendor unwilling to let you test is hiding quality variability.
What to ask for: Right to sample and send modules to an independent lab (or request factory acceptance testing witnessed by your engineer). Insist on accelerated life tests for larger buys.

8) Weak or opaque financials / no bankability evidence

Why it’s a red flag: Financiers, EPCs, and insurers check supplier balance sheets, order book, and warranty reserve. A weak financial profile raises risk that the company cannot meet warranty obligations or maintain spares.
What to ask for: Audited financials (last 2–3 years), bank references, order backlog, and third-party bankability reports where available. Consider escrow or performance guarantees if financial strength concerns appear. (Solar Media)

9) Long, shifting lead times and broken delivery commitments

Why it’s a red flag: Missed deliveries lead to project delays, liquidated damages, and rework. Long lead times without firm inventory commitment are a supply risk.
What to ask for: Firm lead-time SLAs, penalty clauses, minimum stock commitments, and visibility into logistics / shipping manifests.

10) No local O&M, spares, or technical support plan

Why it’s a red flag: For utility projects, you need fast replacement, inverter/module swap plans, and local spares. If the vendor lacks local offices, spares depots, or an escalation matrix, small problems become long outages.
What to ask for: Local service center addresses, spare-part lead times, escalation matrix, and a samples/spares holding requirement in the contract.

Mitigation checklist — what a good procurement package includes

• Model-level certificates: IEC 61215, IEC 61730, UL (if required), and region-specific approvals (e.g., MNRE ALMM for India).
• Independent lab reports: PVEL, DNV, TÜV test reports and scorecards.
• PAN files & IV curves for every module type and batch.
• Defined warranty instruments: bank guarantee, warranty insurance, or escrow.
• Factory audit checklist: QA processes, traceability, supplier control, and sampling. Use a recognized bankability guideline or technical checklist as a template.
• Sample validation plan: accelerated tests, field exposure from similar climates, and pilot arrays where possible.
• Contractual safeguards: LDs for delivery, SLAs for yield, and warranty enforcement language.

Real-world reliability considerations (technical callouts)

• PID and LeTID — some modules show rapid early degradation driven by cell and module chemistry. Independent tests reveal vulnerabilities; don’t rely on vendor claims alone.
• Thermal / humidity resilience — panels used in coastal or humid regions must pass damp-heat and salt-mist/ corrosion checks. Ask for test data matching your site climate.
• Mechanical loading — wind and snow load testing matters especially for elevated arrays and tracker-mounted modules. Check IEC mechanical load reports.

Make supplier due diligence non-negotiable