New testing conducted at France’s oldest PV system have shown that its solar modules can still provide performance values in line with what the manufacturers promised.
Those are way more interesting than this single installation with -0.66%:
“Another more recent study carried out by the US Department of Energy’s National Renewable Energy Laboratory (NREL) on 1,700 American sites totaling 7.2 GW of power, showed a median degradation of around -0.75%/year. Moveover, another research focused on 4,300 residential installations in operation in Europe and used different data processing methodologies. Depending on the methods, a median loss of -0.36% to -0.67%/year was obtained.”
Also the article doesn’t mention standard deviation or IQR of the drop, or what efficiency they originally had. Which is the minimum of information I would expect.