Are you sure the sunlight dimming is 90-99%?
This seems quite extreme and I doubt the rovers could actually measure this. They could only measure the reduction in their solar output based on horizontal panels that would obviously get covered in dust.

Vertical panels won't suffer from this.

I have both vertical and horizontal panels in a place where it doesn't rain for 6 months a year and there is plenty of dust. The horizontal panels get covered in dust quickly and need to be cleaned regularly.

The vertical panels stay perfectly clean and almost never need to be cleaned. Wiping off some bird poop is all.

The difference is night & day.