In the late 1980s, when Switzerland was just beginning to experiment with solar power, engineers bolted a few shiny panels onto rooftops, mountain stations, and even utility-scale farms. They probably didn’t expect those panels to still be humming along more than three decades later.

But that’s exactly what a new study shows. Researchers from Switzerland, Austria, and Germany tracked six photovoltaic systems installed between 1987 and 1993 across the country’s dramatically different climates — temperate valleys, snowy mountain huts, and high-altitude research stations perched above the clouds. After more than 30 years, those panels are still reliably producing electricity.

The Surprising Longevity of Solar

On average, the Swiss panels lost just 0.24% of their performance each year. That’s about three times slower than what’s often reported in the literature. In practical terms, most of the panels still deliver more than 80% of their original power — well past the 25-to-30-year warranties manufacturers usually provide.

“This [data] really shows that photovoltaics can last [longer than expected], and it’s an important message to the photovoltaic industry,” lead researcher Ebrar Özkalay at the University of Applied Sciences and Arts of Southern Switzerland, told Chemistry World.

The results are very similar to findings from France last year. There, Hespul, a renewable energy nonprofit, tested the country’s oldest rooftop solar system, installed in 1992. After 31 years, the French panels were still operating at nearly 80% of their original capacity — right in line with the Swiss data. Hespul declared that the results demonstrated photovoltaics’ “capacity to become one of the major sources of energy in France and in the world.”

Together, these studies show that solar panels, even those using outdated tech from decades ago, can keep running for a very long time.

Climate, Materials, and the Solar Recipe

The Swiss study dug into why some panels age better than others. Location turned out to matter. Panels in low-altitude towns, where surfaces can heat up to 80°C in summer, degraded faster. The constant heating and cooling cycles stressed the materials, leading to local corrosion and reduced conductivity.

By contrast, panels mounted in alpine environments weathered the cold surprisingly well. They faced high ultraviolet radiation and wild day–night swings, but they generally retained performance better than their lowland counterparts.

Even more important than climate was what the researchers called the “bill of materials.” Panels built with robust encapsulants, adhesives, and backsheet laminates lasted far longer. Those early 1990s modules used tough EVA encapsulants, Tedlar backsheets, and solid glass/foil structures. Some variants, like Siemens’ SM55-HO “high output” panels, even had different filler materials in the laminate to boost efficiency, which influenced how they aged.

Not every panel held up equally. The oldest models, manufactured before UV stabilizers were added to encapsulants, showed more discoloration and delamination. Others suffered from solder bond failures that cut efficiency. Still, the fact that most continued to perform at a high level after decades in the field is remarkable.

Lessons for the Terawatt Age

Today, solar is no longer a boutique experiment. It supplies over 8% of the world’s electricity and represents 70% of all new renewable capacity added in 2023. As we enter what researchers call the “terawatt age” of photovoltaics, the long-term reliability of solar panels matters more than ever.

The Swiss findings suggest that cutting corners to boost efficiency or lower costs could be a mistake. “The bill of materials — everything that goes into a panel — has a great influence on performance, even when made by the same company,” notes Dirk Jordan, a photovoltaics expert at the U.S. National Renewable Energy Laboratory.

Modern modules are often designed with thinner, cheaper materials. That may drive down upfront prices, but it risks compromising longevity. For instance, in Gujarat, India, many solar installations from 2009–2013 have degraded severely, needing replacement after just 8–12 years, well below the standard 25-year expectation. Causes include micro-cracks, poor build quality, soldering defects, and inadequate maintenance

The old-school panels remind us that durability is just as crucial as efficiency and upfront cost in making solar sustainable. Longer-lived panels mean fewer replacements, lower costs, and a smaller carbon footprint.

The findings appeared in the journal EES Solar.