Solar panels are being produced in staggering numbers as PV generation grows worldwide. The technology is proven but manufacturing standards are highly variable. EcoGeneration speaks to PV Evolution Labs CEO Jenya Meydbray about why developers must be vigilant buyers.

Solar panels may look like a generic commodity but under closer inspection all manner of sins can be revealed. You have to know what to look for, and laboratory technicians at PV Evolution Labs in Berkeley, California, have devised a menu of tests sort the good from the bad.

Chief executive Jenya Meydbray spoke to EcoGeneration about the small and not-so-small irregularities on modules that, unless detected, can render solar projects uneconomic.

We are seeing rapid growth of large-scale solar in Australia. How complacent should project developers be about the panels they are choosing?

Project developers – especially long-term asset owners and investors – should not be complacent about the modules that they procure. Independent testing of commercial PV modules reveals two major issues that buyers must be aware of: first, PV modules with the exact same model number, data sheet and power label can be made of completely different materials and internal components; and second, even small changes in Bills of Materials (BOMs) can significantly impact long-term reliability and performance.

Certifications and warranties do not provide buyers with sufficient protection against the risks presented by these two issues.

Certifications only screen for short-term defects and safety issues, not long-term reliability and performance. Due to measurement uncertainty, warranties almost never fully compensate buyers for performance loss, even when claims are successful and the manufacturer is financially solvent. PV Evolution Labs (PVEL) performs extensive reliability and performance testing through our Product Qualification Program (PQP) on most manufacturers and actively supports developers, often with no cost to the developer.

PV Evolution Labs CEO Jenya Meydbray says uncertainty in measurement means PV panel warranties almost never fully compensate buyers for loss.

From the latest report, can you describe a case where a very small deviation in materials or construction caused unexpected reliability issues.

Our latest report focuses on a case study of two PV modules with identical model numbers, data sheets and power labels that are actually comprised of completely different materials – that is, different cells, backsheets, encapsulants and other key components.

A buyer would have no way of knowing that the PV modules had different Bills of Materials (BOMs) unless they had independently verified the BOMs during production with a factory witness. One module showed 2% degradation and the other module showed 7% degradation after 800 thermal cycles. These divergent results confirm that the modules will perform very differently in the field.

In our 2018 Scorecard, we cited a case study of two PV modules with identical model numbers, data sheets and power labels that had nearly identical BOMs with the exception of the encapsulant. One module showed 2% degradation following PID [potential-induced degradation] testing and the other showed 12% degradation – changing the encapsulant caused the PV module to become highly susceptible to PID.

What level of underperformance can render a project unviable?

The level of underperformance that can render a project unviable is dictated by its unique energy yield and financial models. Relatively “low degradation rates” of about 1.5-3% can render projects with tight financial models unviable.

In a recent study the National Renewable Energy Lab (NREL) determined that increasing the annual module degradation rate from 0.5% to 1.5% will cause the site’s real levelized cost of electricity (LCOE) to increase by 13.6%. This could severely impact the project’s economics, turning a profitable investment into a financial burden for the asset owner.

The impact of site underperformance on project financials is further demonstrated by a poll conducted by PVEL where 70% of survey respondents replied that an underperformance of 3-6% is enough to render their projects financially nonviable.

What are the main causes of panel failure?

Infant PV module failure modes and degradation types include: contact failure in the junction box or string interconnects, solder joint degradation of the cell-to-cell or cell-to-busbar interconnects, glass breakage, loose frames, excessive light induced degradation, light and elevated temperature induced degradation (LeTID) and potential-induced degradation (PID).

Mid-life PV module failure modes and degradation types include: potential-induced degradation (PID), diode failure, cell interconnect breakage, backsheet failure, glass and anti-reflection coating degradation, EVA discolouring, delamination and cracked cell insolation and solder joint degradation of the cell-to-cell or cell-to-busbar interconnects. 

Wear-out PV module failure modes and degradation types include: corrosion and solder joint degradation of cell and interconnect. 

How can buyers test panels before committing to a bulk order?

Buyers should require that manufacturers conduct extended reliability and performance testing from a reputable independent lab such as PVEL. Our most recent Product Qualification Program (PQP) for PV modules requires the following testing: thermal cycling, damp heat, ultraviolet testing, dynamic mechanical load sequence, potential-induced degradation, field exposure, light-induced degradation and PAN and IAM characterization.

Our product qualification program is updated annually in response to feedback from our downstream partners, global research institutions and manufacturers. Our next PQP will also include backsheet durability sequence and light and elevated temperature induced degradation (LeTID) testing.

Typically the manufacturer pays for testing and PVEL provides reports from testing to downstream partners on a complimentary basis. PQP testing is conducted at the Bill of Materials (BOM) level and requires that BOMs are verified by a third party during production. This verification process is known as a factory witness. A factory witness allows buyers to determine the BOM used in testing and then specify that the same BOM that performed well in testing is used in their bulk order. They can then be confident in the long-term reliability and performance of their selected modules.

Do reputable brands produce bad batches? How does this happen?

Reputable brands do produce bad batches and small, lesser known companies can produce great batches of modules. Unsurprisingly, we’ve found that bad batches are often a response to cost pressure. They typically occur when material components are changed but are not properly vetted or when quality controls are not strictly adhered to. Every time a BOM component is changed, a new quality manager is onboarded on an existing line or a new factory or factory line is opened, independent PV module testing should be conducted to verify product quality.

Technological advances can also drive reliability and performance issues. The relatively recent phenomenon of LeTID observed in monocrystalline PERC cells is one example.

A manufacturer with a 5GW production capacity – which is pretty common nowadays – produces roughly 40,000 PV modules per day every single day of the year. It’s challenging to manage quality and consistency with this staggering quantity of production volume.

Have you tested bifacial panels? How do they stand up?

We are currently testing several bifacial product lines in our Product Qualification Program (PQP) for PV modules. The results will be available in our 2020 Scorecard. We are also currently testing bifacial PV modules in two large-scale research projects that are partially funded by the US Department of Energy.

While the full results from our studies are not yet available, initial testing shows that Bills of Material (BOMs) are as important to the extended reliability and performance of bifacial PV modules as they are for monofacial modules. BOMs also have a significant impact on the additional energy yield delivered by bifacial modules. Bifacial modules built with glass/glass construction will have different degradation modes than glass/backsheet construction. These nuances must be properly vetted when qualifying new products. 

Do manufacturers take issue with your testing methods, in particular the thermal cycling?

Manufacturers rarely challenge the testing performed in our PQP. They’re often at least as interested in understanding long-term reliability of their products as the downstream community. 

The reliability engineers in the solar industry have been developing accelerated lifetime testing methods for decades, starting with the Jet Propulsion Laboratory Block Buy Program in the 1980s. While testing methods must constantly evolve with changing technology, some fundamental tests such as thermal cycling haven’t changed much. Generally, manufacturers understand that the PVEL PQP is designed for and by their downstream clients. As a result, they usually accept the test durations. 

Only four out of 15 brands have scored well since 2014. What can we deduce from that?

The supply landscape has been in a state of flux since 2014. Some of the manufacturers listed in our early Scorecards, such as SolarWorld, are no longer even producing PV modules. It’s also important to emphasize that participation in the Scorecard is voluntary and that some manufacturers choose not to be listed – this may occur when a manufacturer is a Top Performer in some but not all tests.