Imagine this: your 25-year solar project is commissioned, the financial model looks solid, and investors are confident. But three years in, the energy yield is consistently 5% below projections. The numbers no longer add up, and your Power Purchase Agreement (PPA) is at risk.

What went wrong? The culprit might be a silent performance killer you never accounted for: Light and elevated Temperature Induced Degradation, or LeTID. This phenomenon can erode a solar module’s output far beyond the linear degradation that most financial models assume, creating a critical blind spot for asset owners and investors.

What Exactly is LeTID (and Why Should You Care)?

Think of LeTID as a solar cell getting a „fever“ early in its operational life. It’s a specific degradation mechanism, primarily seen in PERC (Passivated Emitter and Rear Cell) technology, that is triggered by sunlight and heat—two things your solar farm has in abundance.

While all modules degrade over time, LeTID is different. It’s a rapid, non-linear power loss that typically occurs within the first few years of operation when module temperatures are between 50°C and 90°C. This degradation can be significant, ranging from a 3% to a staggering 10% loss in power.

The real challenge? LeTID is sneaky. It often emerges after standard Light Induced Degradation (LID) has stabilized and can sometimes be followed by a slow, unpredictable regeneration phase. This uncertainty makes it nearly impossible to model accurately without specific testing, creating a massive gap between the idealized degradation curve in a financial model and the real-world performance of an affected module.

This gap between forecast and reality is where financial risk multiplies. A PPA is a promise of performance over 25 years. If unaccounted-for degradation compromises that promise, the project’s entire bankability is called into question.

The Billion-Dollar Question: Is TOPCon Technology Immune?

As the industry transitions to new cell architectures like TOPCon (Tunnel Oxide Passivated Contact), many manufacturers market their products as „LID-free.“ This is a compelling claim, but it can be misleading.

While TOPCon cells aren’t susceptible to the exact same degradation mechanism as PERC LeTID, they are not entirely immune to other forms of light-induced degradation. Researchers and test labs are observing different, yet equally impactful, degradation behaviors, sometimes referred to as „TOPCon-LID“ or related to UV light exposure (UVID).

Ultimately, every new cell technology and unique combination of materials has its own degradation profile. Assuming any new technology is completely stable without verification is a risky bet. The financial imperative remains the same: quantify any potential power loss to ensure your models reflect reality, not just marketing claims.

From Uncertainty to Bankability: The Role of Controlled Testing

So, how do you fight a hidden enemy like LeTID? You turn the lights on.

Standard IEC certification tests are crucial for safety and initial quality, but they aren’t designed to fully characterize these complex, temperature-dependent degradation mechanisms. To get bankable data, you need a dedicated, controlled testing protocol that simulates real-world conditions.

Here’s what that process looks like:

1. Establish a Baseline: The module is first measured under Standard Test Conditions (STC) using a high-precision flasher and Electroluminescence (EL) imaging to establish a precise starting point for power output and cell condition.
2. Apply Controlled Stress: The module is placed in a climate chamber where it is subjected to specific light intensity and elevated temperatures, forcing the LeTID effect to occur in an accelerated, measurable way.
3. Map the Degradation Curve: The module is periodically removed and re-measured. This cycle of stress and measurement allows engineers to plot the exact degradation curve—including any subsequent regeneration.
4. Deliver a Precise Profile: The final result is a degradation curve specific to that module’s bill of materials (BOM), providing the exact data needed to build an accurate energy yield model.

This data-driven approach transforms uncertainty into a known variable. It allows you to move from guessing to knowing.

How Precise Degradation Data Secures Your PPA

Armed with a precise degradation curve, the conversation with investors and lenders changes completely.

• Your financial models become robust. Instead of using a generic 0.5% annual degradation factor, you can model the true performance curve, including any initial drop-off.
• Your energy yield forecasts become reliable. This builds confidence and removes the biggest source of uncertainty for project stakeholders.
• Your PPA becomes truly bankable. Lenders and investors can see clearly that the project’s long-term performance has been validated, de-risking their investment.

This level of certainty is especially critical when developing new solar module concepts or qualifying new material suppliers. Thorough material testing is no longer a „nice-to-have“—it’s an essential part of financial due diligence. By understanding how your specific combination of cells, encapsulants, and backsheets behaves under stress, you secure the long-term viability of your assets.

Frequently Asked Questions (FAQ) about LeTID

Why don’t standard module datasheets include LeTID?

Datasheets provide a snapshot of performance under highly controlled, short-term conditions. LeTID is a long-term degradation effect that requires specialized testing to quantify and is dependent on the specific materials used in the module, which can vary.

Does LeTID happen everywhere?

The degradation is triggered by elevated temperatures, so it’s a much more significant risk for projects in hot, sunny climates like the Middle East, Australia, or the American Southwest. However, even in moderate climates, module temperatures can easily reach the 50-70°C range required to initiate LeTID.

Can’t I just use a higher degradation factor in my model to be safe?

You could, but it’s a blind guess. Be too conservative, and your project’s financial projections might look uncompetitive, costing you the bid. Be too optimistic, and you risk defaulting on your PPA. Only precise testing provides the data needed to be both competitive and safe.

Is this type of testing expensive?

When you compare the cost of a controlled LeTID test to the potential multi-million dollar revenue loss from a 5% underperforming asset, it’s one of the highest-return investments you can make in project de-risking.

Your Next Step Towards a De-Risked Solar Investment

Hidden degradation risks like LeTID are no longer on the fringes of solar asset management. They’re a central challenge to long-term profitability. As module technologies evolve, assuming they will perform predictably for 25 years without rigorous validation is a gamble no investor should have to take.

The path forward is through data. Understanding the unique degradation profile of your chosen technology isn’t just a technical exercise—it’s the foundation of a secure and profitable solar investment.

If you’re evaluating new module technologies and need clarity on their long-term performance, you can speak with a process specialist to understand the testing methodologies that deliver bankable certainty.