1. This assumes that the way we build solar panels (or whatever) never changes. We lost a lot of steel-making knowledge in the early 20th century. Of course, all that "expertise" was replaced by machines, so it was mostly a loss of obsolete knowledge.

2. The solution is to pocket a fraction of the savings and keep that in your back pocket to maintain a teaching/research corps and to ramp up internal expertise when/if the subsidies stop flowing. Of course, this assumes a level of competence, self-control, and foresight that may be missing in modern legislatures.