Automotive News recently had a report on driving a Tesla Model S electric car from Los Angeles to Las Vegas. You can find a video describing the drive here. What I found more interesting was the reporter’s description of stopping to charge up the car (A flaw in Tesla’s plan: It’s Chargie McVanish, Apr 8). In order to spur interest in its vehicles, Tesla is building out a network of solar-powered Supercharger charging stations. Their website says they currently have nine but plan to get to one hundred by 2015. One is in Barstow, perfectly positioned for a drive from LA to Vegas.
So what’s a reasonable wait to charge your Tesla?
I pulled into Barstow, and both superchargers were in use. Neither owner was anywhere to be seen. So I waited.
After 30 minutes one Tesla owner showed up, and after another 10 minutes of charging, he was on his way. I plugged in, and waited another 40 minutes to get mostly charged up. The other Tesla was still plugged in, hogging the charger, unable to be unplugged.
And that’s the rub: Charger etiquette. The Model S retails between $70,000 and $100,000. These cars are bought by people who are rarely told “no.” They detest waiting.
This is just a fun queuing story. It reflects a basic fact of queuing systems. Large service systems (i.e., one’s with high arrival rates) will need a lot of service capacity but that capacity can be heavily used and still provide good service (in the sense of short waits). Thus they are very efficient. Think of a large truck stop off an interstate. It may have twenty pumps that are almost always busy but drivers rarely have to wait more than a minute or two for their turn.
Conversely, service systems with low arrival rates are prone to being very inefficient. They don’t need an absolutely large amount of capacity to provide good service but that capacity is not going to be very heavily utilized. That’s a Tesla Supercharger station. Even if charging up a car took as little time as filling a gas tank, Tesla would need to provide relatively more capacity than a gas station in order to assure short waits. Throw in that charging takes tens of minutes, and the situation gets much worse. I would venture that Tesla could double or triple the number of chargers in Barstow and still not match the convenience of gassing up. And that is not even accounting for rude behavior of drivers going AWOL while their car hogs a charging station.