I wonder if anyone has tried feeding a skyscraper's lighting rod into a sand battery and let it charge up from lightning alone, so much potential for free energy there.
It would never strike the lightning rod. The entire reason lightning strikes is due to a circuit between the clouds and ground. If you were to put a "battery" like this somewhere, then the resistance would cause the lightning to go where you don't want it.
You just need to use a sufficiently large storage system. One of the proposals of Project Plowshare was to use underground detonation of thermonuclear weapons as a geothermal energy sources.