Heat and Beat: DuPont Calls for Real-World Testing of PV Solar

Solar power is no longer a boutique industry. At least 900 million solar panels are deployed across the globe. Eighty-one percent of those came online within the last five years. From rural villages in India to the rooftops of suburban America, photovoltaic solar is fast becoming a mainstream source of energy.

Every one of those panels is only as good as the materials used to make it. The life of a solar panel isn’t an easy one. Pounding rain, blistering sun and bitter cold hammer away at them day after day, year after year.

The expected lifespan of a solar panel is 25 years, and most of the panels now in the field should have many years of useful life ahead of them. Unfortunately, that isn’t always the case. The surge of solar power installations and ensuing rush to market exposes problems; weak links in solar module durability and reliability are now coming to light.

Every industry has growing pains. When too many solar modules begin to degrade or fail in less than five years, folks in the industry will start to ask: How do we prevent this from happening again? Over the course of two interviews, TriplePundit spoke with experts from DuPont Photovoltaic about this crucial step in continued healthy growth for global PV solar.

Materials matter

Dupont plays a foundational role in the PV solar industry. Its research and development in materials stretch back more than 40 years, long before anyone but NASA was talking much about solar panels.

“We donated materials to the Jet Propulsion Laboratory in a project funded by the Department of Energy to build and develop a 30-year lifetime module,” Dr. Alexander Bradley, principal investigator for DuPont Photovoltaic Solutions, told TriplePundit in an interview at the Intersolar North America conference in July. Those original modules given to JPL are “still cooking” to this day.

Among the many lessons DuPont learned from its decades of experience -- and particularly cogent today -- is that materials matter.

Ongoing field studies by DuPont and others show a “significant and alarming” increase in solar modules failures, particularly with the backsheet: the unsung hero of a solar panel that provides protection and electrical insulation for the module.

"What we’re starting to see more of are quality issues for (backsheet) materials that have been in the field for a relatively short period of time,” particularly in Europe and China, Robert Olsen, Dupont’s global marketing director, said in a follow-up interview.

DuPont's research, as well as reports from downstream customers, reveal persistent cracking, discoloration, and delamination in backsheets made with the polyamide-based material exposed to cycles of UV, temperature and humidity -- the very elements bearing on a solar module's reliability and endurance throughout its lifetime.

While no longer sold into the market, polyamide was "popular five or six years ago," Olsen explained, and "is a really good example of how we’re seeing failures today of something that was untested at the time.”

Polyamide passed the basic IEC quality standards in place at the time: "mostly fixed-stress tests" geared at "day one performance," Olsen said. They didn't pass the "sequential testing that is more indicative of lifetime performance." If such criteria had been in place at the time to simulate real-world conditions, "these kinds of things would have been flagged, and these growing increases we might not be seeing today."

MAST: Testing beyond day-one performance

DuPont's Fielded Module Program collects data for location, manufacturer, materials and relative performance from 2 million modules spread over 70 global installations and representing more than 30 module manufacturers. “That’s how we learn and develop our products,” Olsen said.

“We share this information with the industry to create awareness and education of the types of issues that are out there and what can be done about them.”

Bill Gambogi, a research fellow based at DuPont's Experimental Station in Wilmington, Deleware, leads that program.

To date, the research shows that less than one-tenth of 1 percent of the failures are related to Tedlar, a backsheet material developed by DuPont. The remaining failures are of polyvinylidene fluoride, PET, and "a large percentage from polyamide."

The current IEC standards for PV solar modules look to "flag early failure,” Gambogi said, "and don't speak to long-term reliability or durability."

"They are aimed at identifying things that really shouldn’t go outside at all,” he continued. “There are multiple stresses in the field and those work together to cause the kind of failures that we’ve seen."

With more than five years of data from the Fielded Module Program, Gambogi and his research team can see beyond day one performance and focus on reliability "over the 25-year market period." And it doesn't take 25 years to do it. MAST, or Module Accelerated Sequential Testing, simulates these multiple, cyclical stresses.

DuPont published several papers, with Gambogi as co-author, demonstrating the correlation between MAST test protocols and expected long-term reliability.

As Dr. Bradley told TriplePundit at the Intersolar conference, the colloquial term for MAST is "heat and beat." Accelerated exposure thermal, UV and moisture pummeling a module in relatively rapid sequence goes far beyond current IEC testing standards.

Testing beyond day-one performance is key to "the strength and health of the industry," Gamogi said. Growing awareness of this problem inside the industry, he projected, will eventually lead to better standards. “Various industry stakeholders must come to an agreement for pushing it forward and what the specifics are. That takes time to get established."

Standards can enforce system reliability, but Olsen says it “doesn’t take a standard” when individual stakeholders understand the economics.

Understanding the economics

Any major energy infrastructure project assesses costs over an expected lifetime of the system. Solar is no different. The economics work for solar when the system lasts 25 years. When all stakeholders understand the "economics of this,” Olsen explained, the industry can correct mistakes made by only considering day-one costs.

The reliability and durability required by the economics of any energy system should theoretically make sufficient standards of production and materials inherent to the market. For stakeholders with a tendency for short-term thinking, the recent “bubbling up” of failures and quality issues have a silver lining for the industry in general.

“A downstream customer -- an installer, owner or a finance company -- [must understand] that when they look at cost, they need to look beyond the ‘day one’ installation cost and look at the lifetime cost of the system,” Olsen said.

DuPont's research proves that point. No need to wait for the standards to catch up to make sound economic decisions.

At the cusp: Building a new energy economy

The common argument among critics of solar power is its intermittency. I argue that in an integrated new energy economy, this is a red herring. The real issue is confidence.

"Solar is still in its infancy," Olsen told us. What the industry needs to "really take off" is, among other things, confidence in the public domain; confidence in government and policy incentives; confidence in the financial institutions that are working to provide capital; confidence in the reliability of the system.

"We're approaching that cusp," Olsen said, where steps the industry take now to these address issues will bear on public confidence. DuPont's message is that fostering the "confidence, health, and growth that we need in this industry" requires an awareness that "preventing a lack of confidence" by adopting higher standards is "critical" to the industry.

Cost pressures, untested materials finding their way into the market, lagging standards: These and other issues now confront an industry still finding its way in a burgeoning marketplace. It needn't be any more than a bump in the road. DuPont and many other have laid the foundation to overcome the inevitable challenges of the new energy economy.

Growing up is never easy.

Images courtesy of DuPont