Earlier quoted context omitted.
Assuming there are that many panels, it is in fact quite easy for any industrialized country to design a weapon that can destroy a square mile of panels or more with a single warhead. They're thin sheets of silicon covered in glass.
A square mile is 2.6 square km. You are replying to someone who said it would be hard to destroy thousands of square km of panels. It would seem that your reply, that "it is…easy…to…destroy a square mile of panels or more with a single warhead", is not to the point. However, by coincidence, your position is right, for two reasons: 1. Single nuclear warheads routinely have blast radii of tens of km rather than, as you…
If terrorists have a nuclear warhead they are going to use it against a city not solar panels. Similarly if terrorists have a weapon that can take out thousands of square km of panels it can easily take out existing powerplants (which btw are not armored or in bunkers - apart from some limited shield on nuclear powerplant cores.
The point here is that solar panels are not more vulnerable to terrorists than the existing infrastructure and are probably less vulnerable due to size and how distributed they are.