French solar photovoltaic association Hespul has revealed that modules in its 1992 Phébus 1 solar power plant still produce around 79.5% of their initial power – after 32 years of operation.
In 2023, the association dismantled 10m2 (equalling around 1kW) of panels to test them in line with international standards. While in a temperature-controlled dark room, the panels were exposed to a 1000W/m2 light flash. Their maximum instantaneous power under these conditions was compared to their factory measurements.
French certification organisation Certisolis and French solar expertise company Isowatt experimented with a corporate sponsorship.
Previous testing was held about 11 years ago, where the results demonstrated that the panels were still producing 91.7% of their 1992 output.
The performance drop was 20.5% on average (0.66% per annum) over 32 years, and 1.11% per annum over the last 11.
1/3 of the installed modules saw a significant drop in performance after 20 years of 33.9% over 32 years (1.09% per annum) whereas another group saw a 13% drop on average.
Other studies
In a statement, Hespul noted that this study mirrored that of the Tlcino SOlare PV system, installed in Switzerland in 1982. As three different manufacturers supplied additives to the encapsulants, that factor was attributed to the variation in performance between the modules.
A study from the US Department of Energy’s National Renewable Energy Laboratory (NREL) showed a degradation of about -0.75% per annum on 1,700 sites in the US equalling 7.2GW.
