Assuming my numbers are correct from the trucking (the part I'm the least comfortable assuming is right), I'll use the specs from a newer version of a solar panel similar to mine: 430W Mission Solar panel from Texas.
The length and width are 82" X 42", which is 24 square feet. I'll assume a 30% reduction in sq ft of land taken up, due to tilting the panels to face the south. We'll call it 17 sq ft per panel. And since these are 430W panels instead of 400W panels, we'll assume we need "only" 325 of them instead of 350 of them.
So that's 325 panels X 17 sq ft/panel = 5,525 sq ft, or about 1/8th of an acre of land. Let's add a little room to walk between rows of panels for maintenance and hold the batteries waiting to be loaded onto the semi, call it 1/6th of an acre of land for solar panels to keep one truck rolling on most days (again, not counting for driving during rainy days).
If there are 2 million trucks on the road, that's 2 million X 1/6th acres = 333K acres needed for solar farms and battery storage to produce 80% of the miles with solar. Of course, that assumes no reduction in throughput for northern EV's driving in the cold and northern solar panels getting less sun exposure. My numbers above are based on what I'm used to in Alabama where we get plenty of sun and our EV rarely has to perform in below freezing temps.
IMHO, with northern weather included we'd need probably half a million acres of solar/battery land to produce 80% of the power needed to electrify today's semis. To make it 100% solar based would need probably twice as much (law of diminishing returns, trying to have a system that works good enough even in the harshest conditions).
Let’s say 666000 acres required for the 2 million trucks.
That’s 1040.625 square miles at 640 acres per square mile.
Taking the square root of that, it would be a square 32.26 miles.
I don’t know the amortized cost for the panels and their maintenance.
Who knows? ....