I still agree with your conclusion though... Capital still dwarfs energy, even if they pay several times what you estimated.
Up until 2012, demand charges from Souther California Edison kicked in at 20 kW at a rate of $17 per kW. One of the first 50 kW quick-chargers in LA county was shut down for months after the owner realized that operating it would tack on an extra $1000 to his monthly bill.
It's an insanely smart offering.
It's admittedly quite a bit more than the supercharger equivalent, but it's far from infinite.
removed my incorrect math re: dollars of fuel per engine
5,000 gallons per cylinder * 6 cylinders * $4 per gallon = $120,000
If you're putting 5,000 gallons through each of six cylinders at $4 per gallon, that works out to $120,000 of gas. Certainly outweighs the cost of the engine by a decent factor.
It's a lot lower than I would guess.
Out of curiosity, what do you think needs to change for them to make sense for most people?
I personally feel the Model S has made an enormous step towards "makes sense" for a lot of people, and I have to think the X will "make sense for most"
Some background: The bulk electricity market (at least in NY state) is run as a giant linear programming problem to satisfy the demand for all regions with a set of supply curves that suppliers bid into the market. They all get paid the same price that the marginal watt (the last watt you need to buy to meet demand) costs.
So, natural gas turbines, who can turn on and off relatively quickly, will bid high and are likely to be the marginal watt. Nuclear plants bid very low and occasionally negative because it actually costs them money to shut down because they then can't start up again soon. So, they want to be sure that they are going to be scheduled.
This is oversimplified and ignores the difference between the day-ahead market and real-time market, products like regulation (we pay money for people to be ready to turn on/off and keep things at 60Hz), and inter-zone transmission)
The point is that a nuclear plant can't suddenly turn on in response to a spike in demand from quickly-charging car batteries. A bigass flywheel or a bigass battery (shameless plug for Sadoway: http://www.ambri.com/) might though.
That works out to about $250,000, or about $10 per Tesla Model S sold to date. Early days and all, but it looks like about $100† tacked on to the selling price of the car covers lifetime supercharger network power use. Capital expenditures to build them probably dwarf their electric bills.
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† To the limits of Fermi Estimation