[dflock]

Musk's comment were intended to demonstrate that powering the US on solar is practical - you don't need to cover the whole country in panels, you actually only need 10 square miles.

You wouldn't actually put all these panels in one place, because of transmission losses, putting all your eggs in one basket, etc...

The point being, that you can power the US with a reasonable, practical amount of panels.

[petre]

You just need to cover the otherwise unused roofs to build what is essentially a distributed power generator. Maybe even use a 10 kWh battery for backup if it's cheap enough (under $1000) for each PV covered roof.

[dflock]

Yes. Tesla/SolarCity are doing exactly that - they're about 400,000 roofs in, so far.