And about the washing, I wonder if it would be worth it to automate the process with a spray of water periodically? You can still wash the panels but I suspect it won't be necessary if there isn't too much dust accumulation? Isn't rain supposed to wash away the dust? What am I missing here?
I don't have numbers, but I suspect it alleviates issues with dust buildup and temperature.
Sadly, my investigations a few years back indicated that a suitably strong and robust 2-axis tracker that would withstand our local winds and snow loads is significantly more expensive than just buying more panels and facing some of them east/south/west to accomplish the same thing. Doing this on an existing shed also avoids some local zoning rules vs a dedicated ground mounted system.
(This assumes that you have enough space, but for grid-scale solar this is not the limiting factor. The costs are roughly in order from most to least: the cost of the inverters and grid connection, the cost of installing the panels, the cost of the panels themselves, then the cost of the land to put them on)
As always ymmv and depends somewhat on your location. I'm around 30 degrees from the equator.
During summer, lying flat gets a lot more power. And more importantly the start and end of the generating period is longer. Ie the panels get more sun in the morning and evening thankfully they were tilted.
In winter the sun is more "from one direction" and obviously is lower on the horizon.
In places where solar panels are used the most, like the Southwest US, there isn't much rain to speak of. Panels get a lot of dust accumulation from Feb-Nov typically, just when they're needed the most.
I do a similar procedure for my house windows. I use a squeegee on those but probably not necessary for panels.
The dirt may not be piling up, but it's far from clean.