Fast car charger economics
As you might guess, my recent switch to an electric car is revealing a variety of things to me, so you will be seeing more on that in the coming period.
Electric cars have always been criticised for their range, the slow speed of charging, and the difficulty in finding places to charge. An early joke about the original Leaf was "it has a 2 gallon gas tank that takes 4 hours to fill and there are hardly any stations." Pretty hard to make electric powertrain sound good when described that way.
Update to today, where Teslas, the Chevy Bolt, the upcoming Leaf and several other cars have ranges over 200 miles. Tesla pioneered this and there is indeed a magic number. These cars can handle all your day to day driving in a city with no anxiety. The range is only an issue when you want to do a road trip or have a rare day of particularly long driving.
With a suitable charging station at home, you can simply recharge the car every night. It doesn't matter if it takes 8 hours. There is a solid case that just plugging and unplugging each night is less work and inconvenience than finding and filling up at a gas station once a week. It's also cheaper and more pleasant. In fact, with 200 or more miles of range, you actually have range for almost a week on a single charge, considering the average car in the USA averages only 40 miles/day. This even allows slower, cheaper "level 1" charge which only restores 40 to 70 miles per night. While at first blush, the idea of using a method of charging that could take 40 hours to finish seems completely ridiculous, it actually works fine most of the time because you don't normally drain a car completely with city driving, and nor do you have to charge it full. (In fact, it's better not to.)
But there are still the road trips, and the rare days of very long driving. People want an answer for that. And Tesla built their "supercharger network." They made it much faster than the standards based high-speed charging, though it still takes much longer than stopping at a gas station, and there still aren't (compared to gasoline) very many stations.
With the supercharger and 250 miles of range, you could pause 1-2 times a day on a long drive for the supercharge. While clearly not as convenient as gasoline, drivers adapt to taking slightly longer rest breaks, and getting a snack or doing some shopping to make the breaks only a minor burden. It works. You can take a great road trip in a Tesla and many do. You can't, however take any road trip. You are constrained to the popular routes Tesla had install chargers for, with only modest variation. But for many people, this is not too shabby at all. Gasoline cars are readily available for rent for the other road trips.
When Tesla began this, they made the supercharging free. They wanted people to really feel these cars were capable of road trips, and free is a good incentive. The superchargers were mostly along the highways and not in cities. As they put some in cities, people got attracted by the free price, not surprisingly, and started using them for general recharging of their car, instead of at home where they had to pay.
This got worse as the number of Teslas grew, and in particular the recent surge in model 3 sales had most of them come with 6 months of free supercharging. The result is that many superchargers, particularly urban ones, are full, with people waiting in line, at many times of the day. Waiting in line is obviously a serious negative, but full supercharger stations also charge you more slowly, since the superchargers are paired and share their power between the two stalls.
This was costing Tesla a lot, so they just announced they will stop the free supercharging perk. They must honour the legacy cars which got it, but they are in a cash crunch and can't afford to expand the network. They have declared the superchargers, when paid for, will be priced at a break-even level, but they recently bumped the price quite high. The new price of 34 cents/kwh in California is 9 cents/mile -- which matches the cost of gasoline for an efficient hybrid car. A big jump from the 3 cents/mile you get with the national average grid price of around 11 cents.
A fast charger is not a gas station
The problem is that when people supercharge near their home, they are not doing electric car ownership right. If you treat the supercharger like your gas station, it's a pretty crappy gas station, with long waits and super-slow fill-ups. You have an inferior experience to gas car ownership. If you do most of your charging at home you get a superior experience. The supercharger should be viewed as a fix to the edge problems of electric cars.
In addition, many people drive a bit out of their way to get to the local supercharger because it's free. But driving still causes depreciation like in any car, with a cost of driving of at least 25 cents/mile. So if you head 5 miles out of your way (10 miles RT) you use up $2.50 of car life in order to save $4 of electricity. Not too smart. (Gasoline drivers are notorious for this, driving several miles to get gasoline for a few less cents/gallon.)
Getting the true number for incremental miles is difficult. Usual estimates for per mile cost of a fancy car range 60 to 70 cents/mile, but that includes time based costs as well as per-mile based costs. See the comments for more details. 25 cents/mile seems like a reasonably safe number.
How to find a balance
I think Tesla could have solved this problem without giving up on the perk. As I wrote, superchargers are there for road trips and special days. You don't want to supercharge every day -- it causes more degradation of the life of your battery than regular charging does. If you supercharge too much, Teslas are programmed to cut you off for full speed supercharging forever. But people are foolishly doing it in their home towns just to save the money. Some are also doing it because they don't have any charging at home or work. They may not own a parking space or garage. At the present time, I believe that electric cars are not ready for people who can't charge at home or work on a mostly-daily basis, but people are buying them.
The answer is to give free or discounted supercharging only at superchargers not near your home. The car knows where you live (it parks there most nights) so you can't fake your address. Let people feel good about taking road trips and not worrying about power, as the network was designed to do, but let the people driving close to home use the superchargers only for unusual situations, and pay for it when they do.
Legally, this would only be applied to new cars going forward, since a deal is a deal. But it would actually benefit those older owners simply because the crowding would go away. It might also cause a price benefit. While Tesla has not confirmed this, I suspect that when they say they are running the superchargers "not as a profit center" they mean that the revenue from paying customers is matching the costs of the superchargers, not the "revenue" from people with free supercharging. If so, this means the people paying are subsidizing those who get it free, and this causes the gasoline level prices.
Superchargers today also charge the same price all day, while electricity actually varies a great deal during the day. Most Tesla drivers supercharge from 5pm to 9pm, which is unfortunately in the peak zone of electrical demand. Almost nobody is charging after 11pm when the cheap power becomes available. It could make sense to offer free supercharging, even locally, after 11pm.
Pay to skip the line
Another option which would raise the ire of those who got lifetime supercharging would be to let those who are paying go to the front of the line. In this event, people with free supercharging could elect to pay or wait or would probably do less local supercharging. This could be implemented by having people indicate the desire to supercharge and pay when they arrived at a station with a line. With such people waiting, free stalls would only work for those who registered in that queue, until the queue is gone. (People could block stalls in anger, but I suspect this would backfire.)
Of course, once cars can move themselves at night, you won't need charging in your house at all. The car will head off to a charging location nearby to charge itself at some reasonable rate. In fact, the charging rate will depend on demand. The car has all night (or all day if you don't need it until commute time) so it will be the number of stalls available that governs the charging rate. We can't have supercharging in our houses, because most houses only have 24kw or 48kw of total power available to begin with. Drive-in stalls will all have lots of power.
And of course, some day, Tesla could implement automated movement at superchargers so you did not have to wait in line.