(consider that the Roadster on a 240V/70A charging circuit should need 3.5 hours to go from 0-100%).
this means about 16 800 VA (let's say watts and consider the result a maximum value)
for 3.5 houres, it would cost less than 7$ here... !!? what? 7$ vs 40$ to fill my gaz car?
where's the catch? And a 70A line, this is freaking dangerous.