[cmurphycode]

You could estimate this in a couple different approaches, here's one.

Tesla Model 3: 26 kwhr / 100 mi Model S: 33 kwhr / 100 mi Model X: 39 kwhr / 100 mi

Hard to say where the balance of supercharging comes from (more expensive models more likely to have it free, but maybe less likely to use?) so let's be generous and call it 30 kwhr/100mi

I pay 24 cents per kwhr but I hope their average price is more like 10 cents (not even counting the solar...)

So each 100 miles charged would cost $3.

So 100 million dollars spent giving out electricity would generate 3.3 billion miles charged.

Back in september there were 20 million telsa miles driven per day, but a year long projection would be hard given the fast growth of model 3. let's just say 20M per day. That's about half of the year's miles driven covered with 100M.

I can't imagine that even 1/2 of the total miles driven are charged by superchargers. So I am inclined to agree with you; the free-supercharging-electricity costs are probably a small piece of the total 500M.