One idea was to create a necklace of satellites in geosynchronous orbit around the Earth that could collect the undiluted energy of sunlight, convert it to microwaves, and then beam it back home.
This is the sort of thing that can cause global warming, since it would capture energy that would otherwise not hit the Earth.
Those satellites would make a great space-based weapons system too. Just re-aim the microwave beam away from its collector and at your chosen target and WOW!