The Solar Modules Installed in France in 1992 Still Deliver 79.5% of Their Original Output

The French association Hespul was founded in 1991 with the aim of building the first grid-connected photovoltaic power plant in France. After the inauguration of the Phébus 1 plant on June 14, 1992, in Ain, Hespul decided to expand its activities to promote photovoltaics in France, which was almost non-existent at the time.

The association has now announced that some 10 m² of panels, corresponding to a power of around 1 kW, were removed from the plant last year and subjected to a series of tests in accordance with international standards. The panels were placed in a temperature-controlled darkroom and exposed to a light flash of 1000 W/m² to measure their maximum instantaneous power. This value was then compared with the factory measurements.

The tests were made possible thanks to the sponsorship of the French certification body Certisolis and the French solar energy specialist Isowatt, who carried out the flash as well as the disassembly and reassembly of the modules. Tests have shown that after 31 years of operation, the modules still produce an average of 79.5% of their original output. Previous tests carried out 11 years ago found that the panels produced 91.7% of their original output. “This result exceeds the performance promised by the manufacturers, who claimed that the modules would still deliver 80% of their output after 25 years,” says Hespul.

The drop in performance averaged 20.5% or 0.66% per year over 31 years and 1.11% per year over the last 11 years. For the same series of modules, two categories were observed: the part whose drop in performance after 20 years is very significant (1/3 of the installed modules): on average 33.9% over 31 years or 1.09% per year. And another whose decline is in line with the 2012 tests: an average of 13% over 31 years or 0.42% per year.

“These results confirm the findings of various scientific studies on the subject,” the association continues, such as the TISO-10 photovoltaic plant (TIcino SOlare), which was connected to the grid in Switzerland in 1982. The tests carried out with the Swiss system revealed differences in performance between the individual modules, which were attributed to additives in the encapsulants supplied by three different manufacturers.

Another recent study conducted by the US Department of Energy's National Renewable Energy Laboratory (NREL) on 1,700 US sites with a total capacity of 7.2 GW found an average degradation of around -0.75%/year. Further studies focused on 4,300 operating private plants in Europe and used different methods of data processing. Depending on the method, an average loss of -0.36% to -0.67%/year was found.

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