7 Procurement Checks to Avoid PV Module Lemon Risk

Investing in solar is a long-horizon decision. The modules you procure determine not only day-one output but also years of performance and O&M exposure. “Lemon risk” refers to receiving defective or underperforming PV modules that quietly erode yield, raise service costs, and shorten the usable life of the system. This guide consolidates practical, verifiable steps so buyers can reduce that risk before, during, and after procurement.

Why Quality Matters

Degradation & Failure Modes (What to Expect, Not Fear)

Fielded PV modules can exhibit light-induced degradation (LID), potential-induced degradation (PID), hot spots, interconnect fatigue, backsheet cracking, delamination, and connector issues. Environmental stressors—heat, humidity, UV, wind loading, soiling—can accelerate these mechanisms. The goal of procurement quality control is to prevent shipping obvious defects and to screen designs that are more likely to suffer premature loss of power.

Cost of Poor Quality

Poor-quality modules raise replacement rates, increase truck-roll O&M, and depress energy yield. Even small annual losses compound over a project’s life, impacting cash flow and warranty engagement. Sound contracts and testing reduce the probability and the financial severity of these outcomes.

Seven Critical Procurement Checks

1) Vet the Manufacturer—Not Just the Datasheet

Assess financial stability, production scale, BOM transparency, and change-control discipline. Verify up-to-date design qualification and safety certifications (e.g., IEC 61215/IEC 61730). Conduct factory audits to review process controls, EL screening rates, inline flash testing, and outgoing inspection criteria. Request sample EL images and flash data histograms as objective evidence.

2) Put Quality into the Contract

Contracts should define the exact build (BOM lock), acceptance testing, sampling plans, and remedies. Set power tolerance and IV-curve acceptance windows, mandate EL/flash records delivery per batch, and specify corrective actions for non-conformances (rework, replacement, or rejection at seller’s cost). Performance warranties commonly state a first-year step followed by linear degradation (often ~0.4–0.6%/yr in market practice); ensure the wording, measurement conditions, and claim pathway are explicit.

3) Factory Acceptance Testing (FAT) Before Shipment

Perform onsite FAT on randomly sampled pallets: visual inspection, EL imaging (to identify microcracks, finger interruptions, inactive areas), and flash testing (STC) to verify Pmax and binning. Reject lots with excessive EL anomalies or systematic power shortfalls. Document sample plans and keep traceability to pallet/serial ranges.

4) Independent Extended-Stress & Reliability Testing

Baseline design qualification (e.g., IEC 61215) is necessary but not sufficient for long-term reliability. Commission independent labs to run extended or accelerated programs aligned with IEC TS 63209-1 (long-term reliability), and add targeted stresses for your site conditions: PID, LeTID, dynamic mechanical load, salt-mist/ammonia, UV extension, damp heat extension, and abrasion/soiling where relevant. Use results to discriminate among BOMs—not just brands.

5) Incoming Goods Inspection (IGI)

Upon delivery, perform damage checks (packaging, frames, glass), verify labels/serials against purchase orders, and run spot EL/flash on statistically meaningful samples—especially if transit conditions were harsh. Quarantine suspicious lots. This step prevents installing non-conforming modules and shifts the burden of proof upstream.

6) Instrumented Performance Monitoring

Post-commissioning, monitor per recognized guidance such as IEC 61724 (system performance monitoring). Normalize yield for irradiance and temperature to detect abnormal strings or rising mismatch. Early detection enables targeted thermography, IV-curve tracing, and warranty engagement before issues propagate.

7) Warranty Playbook & Evidence Trail

Define a claims process before you need it. Keep commissioning reports, EL/flash archives, IV-traces, and inspection photos tied to serial numbers. For common field issues (e.g., connector overheating), consult engineering notes and incident analyses to prevent recurrence; see, for example, NREL’s discussion of connector-related failures and O&M impacts: NREL Technical Report.

Standard vs. Advanced Testing—What Each Tells You

Installation, O&M, and Design Details Still Matter

Procurement controls cannot compensate for poor installation or neglected O&M. Ensure correct mounting torque, cable management, and connector mating; improper mating/contamination can elevate contact resistance and create thermal hazards (again, see NREL). Implement preventive maintenance and periodic thermography/string testing to keep small defects from cascading.

FAQ

Are standard IEC tests enough?

No. They are essential gates for design durability and safety, but they do not rank different BOMs for your climate. Extended and targeted stresses (aligned with IEC TS 63209-1) provide additional discrimination.

What degradation rate should I assume?

Degradation varies by design, site, and O&M. Many performance warranties use a first-year step followed by a linear rate that is often around one-half percent per year in market practice. Use monitoring (e.g., IEC 61724) to measure your actual site behavior.

When should I trigger a warranty claim?

When evidence shows non-conformance to contract specs or warranty terms: serial EL anomalies, IV-curve deviations, persistent hot spots, or systematic Pmax deficits. Keep a clean evidence trail tied to serials and purchase lots.

Bottom Line

“Lemon risk” is manageable. Combine contractual rigor, pre-shipment verification, independent reliability testing, disciplined inbound inspection, and data-driven monitoring. You’ll reduce surprises, protect cash flows, and preserve long-term performance.