My impression is that there is no premium for installing solar, as it's virtually the same as running a new branch circuit - service panel work, junction boxes, conduit, wire sizing. Just ask in your area what a journeyman electrician gets.
That's a hard question because it's not a huge business.
I'd actually thought of starting a business install solar panels but actually, the classes are a bit pricey.
Mostly, the only part of the electrician that's needed is for tying into the grid. I run my basement on solar power but you have to be certified to tie into the grid, thus, you may be better off joining a union and being a normal electrician as far as pay and work goes.