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By Jenya Meydbray

Solar panel warranties and service life expectations have risen steadily since the 1980’s, from the 5-year warranties of yesteryear to the standard 25-year warranties we typically expect today. While installed panels have demonstrated evidence of this impressive operational life, there are, unfortunately, many examples of panels and systems underperforming. This can result in negative investor returns, adverse impacts on the technology’s general bankability, and lagging consumer confidence.

We can mitigate these technology risks by deploying strategic and comprehensive quality control programs, and establishing stringent quality objectives that will have a trickle down effect on the industry as a whole. As the industry continues to expand, and as the technology evolves, it will be critical to continue to develop and deploy aggressive quality assurance programs and to relay the data collected into the next generation of manufacturing. Establishing such programs has a double-fold effect, as it increases the reliability of successive generations of the technology while also providing usable data to help substantiate financial investments in current project development.

Reality from the Field

The objective of any solar panel supply quality management strategy is to avoid procuring panels that exhibit performance degradation worse than expected. There are more than 600 panel manufacturers globally active today, exhibiting a broad spectrum of manufacturing techniques and quality control practices, thus, demonstrating a wide range of product quality and reliability. Quality assurance programs must be versatile as well as extensive. The optimal quality assurance method will depend on the solar panel supply strategy utilized. Before diving into these methods, it is helpful to have a clear understanding of common solar panel failures seen in the field. Developing an understanding of how solar panels age in the field will highlight technology risks and enable one to develop an effective quality assurance strategy.

Failure mechanisms seen over the past several decades cover a wide range of locations and material sets. It is important to note that the majority of failures seen in the field are a result of deviations in the manufacturing process that contribute to product quality issues, and are typically not caused by fundamental design flaws. Several of the most commonly observed solar panel failure behaviors in the field are: hotspots due to solder joint degradation or cell cracks, which can propagate once initiated leading to diminished power output; encapsulant and backsheet degradation and yellowing, which damages the optical properties of the module package and diminishes the amount of light that is able reach the cell; loosening electrical connections in the junction box, resulting in arcing and increased risk for fires; and high voltage Potential Induced Degradation (PID) which can result in significantly reduced power output. All solar panel degradation also contributes to module mismatch over time which adversely impacts power plant performance, since different modules degrade at different rates.

Over the past several decades, significant effort has been dedicated across the industry to understanding long-term solar panel aging behavior. Typical projections used to support project finance estimate a 0.5% per year degradation rate with very minimal catastrophic failure events. Industry experience has taught us that while this level of quality and durability is attainable, it is not necessarily a given. This is where due diligence at the project level is absolutely critical to the life and performance of your project and the health of your investment.

Most solar panel underperformance issues are kept quiet; understandably, since no manufacturer, developer, or investor wants to concede any deviations from high quality. Figure 1 highlights several recent industry activities exploring solar panel aging behavior. These findings highlight the wide range of solar panel reliability and durability seen in the marketplace and demonstrate the importance of understanding what you are purchasing through sophisticated up-front technical evaluation and ongoing monitoring of panel aging behavior. Sourcing from ‘tier one’ suppliers does not remove technology risk either, as many of these respected suppliers have recently experienced major product failures and recalls due to rapid performance degradation, arcing in the junction box, cell cracks, degrading glass coatings, and junction box adhesive failures. Some of the populations recalled have included all production from an entire year.

The Importance of Independence

The necessity of adopting a world-class quality assurance program is underscored by the results of field testing from the JRC European Commission, which presents performance degradation after long-term outdoor exposure by module type. This study looked at the aging behavior of 103 modules from 20 manufacturers subjected to 18-24 years of grid-connected operation. The effect that these real world operating conditions had on the module types varied considerably (Figure 2). Looking across this data pool, an investor or developer can make more intelligent decisions; understanding the aging behaviour of available modules on the open market leaves the buyer less vulnerable to assuming elevated technology risk. Of course, a two decade test is unrealistic when evaluating your panel suppliers. Fortunately, sophisticated and experienced 3rd party PV testing labs utilizing best practices for solar panel supply quality assurance are able to identify defective and underperforming panels in a timeframe that is consistent with tight project development schedules. The solar industry’s recent trend to a buyer’s market makes this the perfect time to deploy rigorous supplier evaluation practices to minimize such technology risk. Enacting a quality assurance program during project development considerably reduces the probability that quality issues will adversely impact the industry’s general bankability and perception as a mainstream power source, as seen in parts of Europe. The wind and residential solar hot water industries suffered tremendous setbacks in the U.S.A. due to quality issues that took many years to recover from. Some would argue that the solar hot water industry never fully recovered.

What would best practices in due diligence look like? It depends on your sourcing strategy. There are essentially two different ways to define a sourcing strategy; one is to build a strong large volume supply relationship with a single supplier, and the other is to procure smaller volumes from various suppliers. These high level quality assurance programs are outlined in Figure 3.

Pushing beyond Existing Protocol

The supplier level quality assurance program requires an intensive relationship with a supplier, ensuring that their quality controls meet and exceed your own with a rigorous supplier qualification program. This would entail a detailed factory audit, and a combination of Reliability Demonstration Testing (RDT) and Ongoing Reliability Testing (ORT) to evaluate a module’s robustness and a manufacturing facility’s ability to produce a consistent product. The objective of the factory audit is to identify opportunities for improvement and threats to consistent product quality. A factory audit establishes a close relationship between the customer and supplier and is critical to fostering a mutually beneficial and long term supply relationship. A new RDT protocol was developed collaboratively by PV Evolution Labs, NREL, Sandia, and Black & Veatch, and investigates a module’s long-term environmental sensitivities and degradation mechanisms. Real world failure mechanisms are stimulated in sophisticated environmental chambers within a controlled laboratory environment and module characterization techniques are utilized to track the performance of the panels as they progress through the protocol. Panels from two suppliers that exhibit identical performance out of the box can have drastically different performance over time, which has a direct impact on investor returns, and can assist in shaping project decisions. Manufacturers subjected to the RDT will exhibit a broad range of performance. This strengthened reliability and durability assessment protocol is designed to differentiate the robust modules from their less-robust counterparts. ORT requires pulling finished modules periodically from the end of the manufacturing line and subjecting them to abbreviated accelerated lifetime stress testing. By monitoring the panel to panel degradation variability of several critical parameters, one can identify and quarantine quality issues if and when they are encountered. Because of the relatively small sample size, ORT is designed to identify failures that affect large populations. This process does not replace but rather compliments the module manufacturer’s internal process controls and quality management systems. The overall objective of the supplier level quality management program is to ensure that the processes and team are capable, the products are robust, and that they are produced consistently.

The project level quality assurance program is appropriate for the more typical sourcing model in project development. This program forgoes a full-fledged factory audit, though it may include a short factory visit (so-called ‘witness during manufacturing’), and will, instead, focus on rigorous module testing to form the backbone of this approach. This testing program is initiated when panels start arriving at the project site; however it is critical to establish contractual expectations with the supplier if a quality issue is identified. There are several components of this quality assurance strategy, Lot Acceptance Testing (LAT), Latent Defect Screening (LDS) and Ongoing Degradation Testing (ODT). LAT ensures that the developer or investor is receiving the power they paid for. This is essentially a 3rd party validation of the factory flash tester accuracy. LDS evaluates potential reliability and durability defects caused by manufacturing drift. The objective is to determine if the manufacturing process is producing panels of the same quality as the day they first went into production. As discussed previously, manufacturing deviations drive the majority of solar panel quality defects and failures seen in the field. ODT is initiated post-commissioning and is a proactive means of monitoring for warranty issues. It involves temporarily uninstalling a small sample of panels annually and subjecting them to laboratory characterization to ensure that the modules continue to meet their specified requirements as they age. Remote monitoring has great value but is not sufficient to determine warranty issues as seen in remote monitoring data from solar power plants (see Figure 4). While a general downward trend is evident it is impossible to determine if the degradation rate is consistent with up front projections of long-term performance.

An Ounce of Prevention Is Worth a Pound of Cure

Increasingly, the industry is acknowledging that it is counterproductive to require testing that doesn’t correlate with field experience. Product underperformance and recalls can take a very long time to identify in the field and can decimate investor returns. The cost of a world-class quality program is typically less than one penny per watt (< US$0.01/watt). A 5 MW recall would result in lost plant revenue of US$90K per month, and additional costs of about US$0.50 per watt, which is typically absorbed by the project owner, not the module manufacturer. These additional costs are driven by field labor, logistics, administrative, and other expenses. The impact to a company’s image and bankability, as well as the public perception of solar energy, could be significant.

Quality deviations happen in every industry; it is inevitable. A quick search on the U.S. consumer product safety commission shows 39 product recalls and safety issues in June 2011 alone. Blindly procuring and installing panels leaves your investments at risk of underperforming. Implementing a world-class quality assurance program will effectively minimize the technology risk associated with a solar investment, further enabling solar’s shift towards becoming a mainstream, financeable, energy source. Defining clear quality expectations with your solar panel supplier and using measureable and quantifiable data are fundamental to increasing reliability as the market expands to meet demand. Only when quality and durability are truly considered a hallmark of the industry, can we consistently ensure project performance, and ultimately meet the dream of mainstreamed solar energy generation.

Jenya Meydbray is Co-Founder and CEO of PV Evolution Labs (www.PVEL.com.), North Americas premier solar panel performance and reliability lab. An advisor to leading solar companies, Meydbray has developed methods of evaluating long-term solar panel performance for product development and bankability. He researches, speaks and consults on the development and deployment of solar energy, including accelerated test methods for high efficiency silicon solar cells and modules, reliability outsourcing strategies, manufacturing quality best practices, and developing bankability packages for large scale solar project finance.