Imagine commissioning a multi-million-dollar solar project. You’ve done your homework, selecting modules from a well-known „Tier-1“ supplier with perfect-looking datasheets and a competitive price. For the first two years, everything runs smoothly.
Then, performance reports start to trickle in, showing the plant’s output is dipping—slowly but surely. A field inspection reveals hotspots, cracked cells, and signs of premature degradation, issues that weren’t supposed to happen with a top-tier product. The warranty claims begin, and you realize the „bankable“ choice you made was based on a brand name, not a guarantee of real-world performance.
This scenario is more common than you might think. The solar industry has a deeply ingrained habit of relying on Tier-1 lists as a primary proxy for quality. But the uncomfortable truth is that a Tier-1 ranking is not a certificate of quality. It’s a measure of financial health and production capacity, telling you almost nothing about the durability of the specific module you’re installing.
To build truly resilient and profitable solar assets, we need to move beyond these lagging financial indicators and embrace a framework built on verifiable test data.
The Tier-1 Myth: Why Financial Health Isn’t Product Quality
The term „Tier-1,“ popularized by BloombergNEF (BNEF), was created to help financial institutions assess a manufacturer’s risk of bankruptcy and its ability to honor warranties. To be on the list, a company must have supplied its own branded products to a certain number of projects financed by non-recourse debt from multiple banks.
While it’s a useful metric for financiers, for an engineer, an EPC, or an asset owner, it leaves critical questions unanswered:
- Is the Bill of Materials (BOM) consistent? Are the cells, encapsulants, and backsheets in today’s production run the same quality as those in the module that earned its IEC certification two years ago?
- How effective is their process control? What percentage of modules come off the line with invisible microcracks that will become major problems later?
- How will the module actually perform after 15 years in a harsh environment?
Relying solely on a Tier-1 list is like buying a car based on the manufacturer’s stock price. It speaks to the company’s size and financial stability, but it doesn’t tell you if the engine is reliable or if the brakes will last. To understand that, you need to look under the hood.
A New Bankability Framework: From Assumptions to Evidence
Instead of asking, „Is this supplier Tier-1?“ we should be asking, „What does the data say about this specific module?“
A robust evaluation framework replaces vague assumptions with a quantitative scoring matrix based on physical tests. This approach provides a true, data-driven bankability index to compare suppliers and make decisions with confidence.
This shift in perspective allows you to identify top performers, not just big names. Here are the five pillars of this evidence-based framework.
1. Bill of Materials (BOM) Consistency
The module that earns a certification is often a „golden sample“ built with the best available components. To cut costs, however, manufacturers may later substitute cheaper encapsulants, backsheets, or cells in their mass production runs. This „BOM deviation“ is a primary cause of premature field failures.
What to look for: Proof that the materials in the modules being delivered today are identical to those specified in official certification reports. The only way to be certain is through independent verification. Prototyping with a supplier’s materials on a controlled production line, for instance, allows you to validate the exact BOM before committing to a large order.
2. Post-Lamination Electroluminescence (EL) Yield
An Electroluminescence (EL) test is like an X-ray for a solar module, revealing hidden defects like microcracks, finger interruptions, and inactive cell areas invisible to the naked eye. While most manufacturers perform EL tests, the crucial metric is the post-lamination yield.
The lamination process—where the module sandwich is heated and pressed—is the most mechanically stressful part of production. A high post-lamination EL yield (>98%) signals excellent process control and high-quality cells that can withstand manufacturing stress. A low yield indicates a sloppy process that is essentially „baking in“ future failure points.
Verifying this requires observing production runs or conducting independent lamination trials to see how materials and cells hold up under industrial conditions.
3. Thermal Cycling (TC) Resilience
A solar module in the field experiences constant temperature swings, from freezing nights to scorching afternoons, adding up to thousands of stress cycles over 25 years. A Thermal Cycling (TC) test simulates this by exposing modules to extreme temperatures (e.g., -40°C to +85°C) for hundreds of cycles.
What to look for: The power degradation after the test. A robust module might lose less than 2% of its power after a TC600 test (600 cycles), while a poorly constructed one can lose over 5%—a devastating blow to a project’s long-term financial model. This single data point is one of the most powerful predictors of long-term durability.
4. Potential Induced Degradation (PID) Resistance
Potential Induced Degradation (PID) is a silent killer of solar performance, especially in hot, humid climates. It occurs when a voltage differential causes ion migration between the solar cell and the module frame, leading to a steady loss of power.
What to look for: Successful completion of rigorous PID tests (e.g., 96 hours at 85°C, 85% relative humidity, and 1,000V or 1,500V system voltage). A module’s resistance to PID is determined by the quality of its cells and, crucially, the encapsulant material. Without certified test results, you are flying blind.
5. Electrical Safety & Durability (Wet-Leakage)
This test assesses the quality of a module’s insulation, which is critical for preventing electrical shocks and ensuring safe operation over decades. The module is submerged in a water tank, and a high voltage is applied between the shorted connectors and the water bath.
What to look for: A pass on the wet-leakage test indicates that the junction box is properly sealed, the laminate is free of defects, and the edge sealing is robust. It’s a fundamental check on manufacturing quality and a non-negotiable for system safety—a core component of comprehensive reliability testing that validates the module’s construction integrity.
Create Your Own Bankability Scorecard
You can start applying this framework today. When evaluating suppliers, create a simple scorecard. Instead of a simple „yes/no“ for Tier-1, ask for the data and rank them on a 1-5 scale for each of the five pillars:
| Evaluation Pillar | Supplier A Score (1-5) | Supplier B Score (1-5) | Supplier C Score (1-5) | Data Source |
|---|---|---|---|---|
| BOM Consistency | Independent BOM Audit / Prototyping Report | |||
| Post-Lamination EL Yield | Factory Audit Data / Independent Test | |||
| Thermal Cycling (TC600) | Third-Party Lab Report (e.g., PVEL, Fraunhofer) | |||
| PID Resistance (96h) | Third-Party Lab Report | |||
| Wet-Leakage Test | IEC Certification Details / Lab Report | |||
| Total Bankability Score |
This simple exercise shifts the conversation from marketing claims to engineering evidence, giving you a far more accurate picture of the quality you are buying.
Frequently Asked Questions (FAQ)
What’s the difference between a Tier-1 list and a bankability report from a lab?
A Tier-1 list ranks manufacturers by financial stability and scale. In contrast, a bankability report from a lab like PVEL or Fraunhofer ISE provides detailed technical data on how a specific module model performs in a battery of reliability tests (like TC, PID, etc.). The lab report is a direct measure of product quality.
Can’t I just trust the manufacturer’s datasheet?
A datasheet provides performance numbers under ideal Standard Test Conditions (STC)—a perfect, sunny, 25°C day. It says nothing about how the module will degrade over time or perform in real-world conditions like high heat, humidity, or shade. Datasheets are a starting point, not the final word on quality.
How often should I test modules from a supplier?
It’s wise to perform spot checks or require fresh test data for every major project or new production batch. Manufacturing processes can drift and material suppliers can change. This ongoing verification ensures the quality you approved initially is the quality you receive in every shipment.
Is this type of independent testing expensive?
Compared to the potential revenue lost from system-wide underperformance or premature failures, the cost of independent testing is a small insurance policy. A 5% underperformance on a utility-scale project can translate to millions in lost revenue over its lifetime, far exceeding the cost of validating module quality upfront.
Your Next Step: From Awareness to Action
Moving beyond the Tier-1 list is about taking control of your investments. It’s about building a foundation of quality and reliability based on data, not just reputation. The next time you evaluate a module supplier, don’t just ask for their Tier-1 status. Ask for their TC600 degradation data, their post-lamination EL yields, and their latest PID test reports.
By asking the right questions, you challenge the industry to be better, pushing manufacturers to focus on what truly matters: building durable, high-performing products that will power our world for decades to come. That is the foundation of true bankability.