Do you clean you panels?

BruceMc wrote:
They look & function the same as they did when I installed them in mid-2010.

Less 2 or 3% - a change small enough to ignore. Normal deterioration of a panel is ~1% a year.

My panels conform to the roof slope, i.e. have 3 or 4 degrees slope. Not totally "flat", and they should not be. A little slope is necessary to prevent water pooling and dust accumulation. Makes washing them easier too. Some dust still accumulates, but larger particles slide down the surface.