5 Critical Questions to Ask Before Investing in Solar Panels

Imagine two solar projects. Both use Tier-1 modules with nearly identical datasheets—promising 25 years of reliable power. Five years in, Project A is performing as expected. Project B, however, is underperforming by 8%, plagued by mysterious degradation that’s eroding its financial returns. What went wrong?

The answer isn’t on the datasheet. It’s hidden in the manufacturing process, the subtle chemistry of the materials, and the microscopic integrity of the solar cells. For investors and developers, relying solely on a supplier’s spec sheet is like buying a house based on the brochure alone. It shows the promise, not the reality.

Real bankability—the confidence that a module will perform reliably for decades—comes from verifying the industrial processes behind the product. This technical due diligence checklist is your guide to asking the right questions and uncovering the risks that datasheets conceal.

The Datasheet Dilemma: Promise vs. Reality

A solar module datasheet is a critical document, but it represents performance under „Standard Test Conditions“ (STC)—a perfect, controlled lab environment of 1000 W/m² irradiance and a 25°C cell temperature. The real world, however, is far messier, with fluctuating temperatures, humidity, snow loads, and wind.

These real-world stressors are what separate a truly robust module from a potential liability. According to research, common but often invisible issues like Potential-Induced Degradation (PID) can affect up to 30% of modules in the field, while microcracks, a „hidden pandemic“ in the industry, can lead to significant and unpredictable power loss over time. This gap between promise and reality is where industrial reliability testing becomes your most powerful risk mitigation tool.

Your Technical Due Diligence Checklist

Use these five checkpoints to look beyond the supplier’s claims and assess the true quality and long-term reliability of a solar module. Each question probes a critical aspect of manufacturing that has a direct impact on your investment’s energy yield and lifespan.

1. How is the encapsulant curing process validated?

Why it matters: The encapsulant is the transparent adhesive layer that bonds the solar cells to the glass and backsheet, protecting them from moisture and mechanical stress. If this material isn’t „cured“ correctly during lamination—a precise heating process—it can lead to delamination, moisture ingress, and catastrophic failure. An improperly cured EVA (Ethylene Vinyl Acetate) encapsulant, for example, is a primary contributor to PID, which can slash a module’s output.

How to verify: Ask for the supplier’s „gel content“ test results for their encapsulant. A proper gel content (typically >75-80%) indicates complete chemical cross-linking, ensuring long-term stability. The gold standard for validation, however, is conducting independent material testing and lamination trials on a full-scale industrial line. This lets you replicate the supplier’s process under controlled conditions and measure the outcome directly, providing objective proof of process stability. A structured approach to optimizing lamination is the only way to guarantee the encapsulant will perform for 25+ years.

2. What measures are in place to detect and prevent microcracks?

Why it matters: Solar cells are incredibly thin and brittle. Microcracks are tiny, often invisible fractures that can occur during cell manufacturing, stringing, or module lamination. While a module might pass initial flash tests, these cracks can grow over time due to thermal cycling and mechanical stress, disrupting the electrical flow and creating „inactive areas“ that reduce power output. This makes them a leading cause of long-term underperformance.

How to verify: Standard visual inspection is not enough. The only reliable way to detect microcracks is with high-resolution Electroluminescence (EL) testing. EL imaging works like an X-ray for solar modules, revealing hidden defects by causing the silicon to light up. You should demand to see EL images from the supplier’s production line, but true due diligence requires independent EL testing of a sample batch. This ensures the images haven’t been cherry-picked and reflect the true quality of the average module.

3. How is the Bill of Materials (BOM) controlled and tracked?

Why it matters: A solar module is an assembly of different components—glass, cells, encapsulant, backsheet, junction box. A supplier might qualify a specific BOM to get certified but then substitute cheaper, lower-quality materials on the production line to cut costs. This „BOM deviation“ is a major risk. A different backsheet could lead to premature cracking, or a new encapsulant could have poor adhesion, leading to delamination.

How to verify: This is one of the hardest things to check without physical access. Ask the supplier for their BOM control protocol. This is also where independent prototyping becomes invaluable. By prototyping new solar module concepts or replicating a supplier’s design in a controlled R&D environment, you can build a „golden sample“ module. This reference module can then be used for comparative testing against modules pulled randomly from the supplier’s production line to ensure nothing has been changed.

4. What is the adhesion strength between the encapsulant, backsheet, and junction box?

Why it matters: Strong adhesion between all layers is fundamental to a module’s structural integrity. Poor adhesion of the backsheet can allow moisture to seep in, corroding the cells from behind. Even more critical is the junction box, which houses the module’s electrical connections. If its adhesive fails, it can detach from the back of the module, exposing live electrical parts and creating a serious safety and fire hazard.

How to verify: Suppliers should be able to provide data from „peel tests,“ which measure the force required to pull apart the bonded layers. These tests should be performed not only on new modules but also after they have undergone damp-heat or thermal cycling tests, which simulate aging in the field. Verifying these claims with an independent lab provides an unbiased assessment of the module’s long-term mechanical stability.

5. Has the specific combination of materials been tested for PID resistance?

Why it matters: Potential-Induced Degradation (PID) is a silent killer of solar projects. It occurs when a voltage difference drives ion migration between the solar cell and the module frame, causing a rapid loss of power. While certain materials are known to be more „PID-resistant,“ the risk is determined by the entire system—the cells, the specific encapsulant (EVA is more susceptible than POE), and the type of glass used. A datasheet claiming „PID-Free“ is meaningless without proof of how the complete material combination was tested.

How to verify: The module must undergo testing in a climatic chamber where it is subjected to high voltage, high temperature, and high humidity for an extended period (e.g., 96 hours). The power output is measured before and after. A truly PID-resistant module will show minimal (<5%) degradation. This is not a test to take a supplier’s word on; it’s a critical validation step for any large-scale investment.

From Checklist to Confidence

Moving beyond the datasheet isn’t about distrusting suppliers; it’s about building a foundation of objective, verifiable data for your investment. True bankability is earned through rigorous, industrial-scale testing that proves a module can withstand the harsh realities of the field for its entire warrantied life.

By integrating these checkpoints into your due diligence process, you transform your role from a passive buyer into an informed investor, capable of identifying superior products and mitigating long-term performance risks before they impact your bottom line.

Frequently Asked Questions (FAQ)

What is the difference between a datasheet and real-world performance?

A datasheet reports performance in a perfect, brief lab test (Standard Test Conditions). Real-world performance is the energy a module produces over 25+ years of seasonal changes, temperature swings, humidity, and other environmental stressors. Industrial reliability testing bridges this gap by simulating long-term stress to predict how a module will actually perform.

Aren’t modules already certified by bodies like IEC? Why do I need more?

IEC certification is an essential baseline—it ensures a module meets fundamental safety and design standards. However, it’s often a „one-time“ test on a specific model. It doesn’t guarantee manufacturing consistency batch-to-batch, nor does it prevent a manufacturer from substituting materials after certification. Independent testing verifies that the modules you are actually buying meet the quality standards set during certification.

What makes a solar module „bankable“?

A bankable module is one that a financial institution is confident will generate a predictable and reliable revenue stream over the life of the loan (typically 20-25 years). This confidence is built on evidence that goes beyond a datasheet—it requires proof of high-quality materials, stable manufacturing processes, and low degradation rates verified through independent, third-party testing.

How can I perform this level of technical testing if I’m not an engineer?

You don’t have to be. The most effective approach is to partner with an independent R&D and testing facility like PVTestLab. These labs provide access to full-scale industrial equipment and process engineering experts who can conduct comparative tests, validate supplier claims, and provide you with a clear, data-driven report on a module’s true quality and reliability.