In my opinion, at least.
Dust devils clean Mars rover solar panels.
A dust devil passed over the rover, and:
"Solar power went from 40 percent reduced to only 7 percent reduced," says Matt Golombek of the Jet Propulsion Laboratory, a member of the Mars rover science team. "That's a 50 percent improvement in a single day."
I guess the math is 60% to 93% total efficiency, which is a 50% improvement. ;-)
18 months ago I attended a live presentation by the MER team called Marsapolooza! and they promised a 90 warranty.
We are at 400% of that and those little guys just keep going and going. . .