Earlier quoted context omitted.
> Every country props up its auto industry, so why worry about a domestic supply? War. In the event a war breaks out, a running auto plant can be re-tooled relatively rapidly into a light and heavy armor plant. It's not even a question of whether allies could supply tanks and troop transports; it's about having domestic capacity to make them because enemies could execute blockades and disrupt allied resource supply.
this. If you look at all the strategic industry subsidies, you will see this common denominator. Corn in the US is stupidly subsidized, so much corn that it ends up in car tanks. But guess who will not have a famine even if the worst war + disasters strike? Car factories might not make good tanks, but the mechanical engineers and tooling knowledge is invaluable and can't be scaled up overnight. Same with solar panels…
Another benefit of domestic factories is domestic innovation. It's much harder for an engineer coming out of university and going through their career working at an office computer terminal to ever make a breakthrough innovation, if they can't step inside the factory to see how things are really done.
If that factory is down the street, it's much easier to do an apprenticeship, get a tour, or chat with the manager about their pain points. If it's in another country, you'll have to schedule a formal visit and you'll probably need to be a very important customer for that to happen.
Grad students coming out of a research lab would tend to focus on getting an extra 0.2% cell efficiency, but it's more likely that the innovation that makes PV competitive is something like reducing the scrap rate, or figuring out how to run cells through the QC machines more quickly.