As I read this piece by Theresa Hitchens at Breaking Defense, describing the potential of directed-energy weapons:
Current DE systems under development for countering unmanned aerial systems (c-UAS) have ranges “nearing 1 kilometer,” AFRL’s study explains, as opposed to other types of counter-UAS capabilities — such as net guns and shotguns — which are only effective at “10s of meters ranges.”
“By 2060 we can predict that DE systems will become more effective, and this idea of a force field includes methods to destroy other threats too,” he said. “Eventually there may be potential to achieve the penultimate goal of a Nuclear or ballistic missile umbrella. It’s fun to think about what that might be in 2060, but we don’t want to speculate too much.”
I could only think “How much energy would a weapons system capable of defending a military base require?” You can’t do that with solar power. I can only speculate that it would require nuclear fission or fusion or some method of producing power that hasn’t been invented yet.