Washington State requires electrical license per the scope of work, IE
Journeyman for any location
Residential
I suspect we will see some type of national effort to get workers installing solar panels.
I know in Washington there is a group who wants to train high school students to do installations, there are some issues with that, minimum age for working with certain tools, etc.
We may see some type of a state limited certification for solar panel installations. However, solar sytems take excellent workmanship and a good knowledge of the codes.