So, how’s this supposedly amazing Tesla going to do road trips? The network optimization problem looks like every other car’s problem, but >3 different network nodes for a different “packet” mean different net topologies:
1. Your home… and then some. Occasionally I hear about people who think the “electric station” metaphor is like using gas stations, but with no gas. MYTH. The clear majority of EV charging will take place at your own home, the exact opposite of the gasoline model now. Tesla’s Roadster and S, with 160-260 miles of range, need public top-ups even less (if at all most days). Really, what does your typical day look like? Your home circuits, as built, deliver “only” 1.4-10 kilowatts (via NEMA 5-15 up to 14-50 outlets), but that’s fine for overnight. The Tesla S ports can take all these, via the appropriate cord/adapters. If you splurge, Tesla will sell you a home unit capable of about 80 amps (~20 kW). Home, then, is the first and most-important tier of the travel network, yet one not on the maps. Without a decent initial charge, #2 and #3 below start to break down.
Now add to that a sub-network of other Tesla owners. That’s right, someone else’s home. Via social networking functions on Plugshare.com, Recargo.com, Plugsurfing.co.uk, etc., owners are volunteering their home facilities to other EV enthusiasts. As you might suspect, this tends to be for emergencies. But, hey, with >200 miles emergencies are few. And yet, Tesla owners seem to be right there volunteering with Toyota, Chevy, Nissan etc. owners.
2. Public charging sites at Level 2. Now say you’re having a long day of errands… longer than 160 miles. You could top up while at work if your employer offers any plug. You could eat at a place near a J1772, compatible with all electric cars sold today (…with Tesla’s J1772 adapter). Heck, if you’re lucky you could stop by a Tesla “dealer” or service center. Vendors are likely to have the 20-kW unit, and likely to be near food/shopping. For that matter, an upscale New Jersey mall and a Vegas casino offer Tesla chargers.
If you’ve been reading this blog, you know Level 2 charging (3-8 kW) still takes hours- certainly for the big Tesla battery packs. Still, some road trips are borderline even in an 85-kWh Model S, such as Chicago to Detroit, Sacramento-Bakersfield, or Washington DC-North Carolina Triangle. So a J1772 stop is in order, while you’re eating or going to the bathroom anyway. (An 85-kW S will outlast most people’s bladders, if not stomachs and colons.) One hour’s lunch will add maybe 15-25 miles of range. Since the cross-compatible J1772 is far more widespread, you’re not reliant on the…
3. Tesla Supercharger sites. Okay, this is what you were waiting for: fast chargers which are Tesla-proprietary, yet free somehow. How’s that? If you’re wondering, a lot of other people are, too.
Supercharger sites have been built by the company along key highways; spacing is about 160-180 miles between city pairs. Each site has industrial power that can support hundreds of amps at >400 volts; some are supplemented with solar-array canopies. The 90-kilowatt Superchargers then juice the compatible Teslas in almost an hour. That’s the Model S, not the Roadster, and S’s with the 60- and 85-kWh pack, not the base 40 kWh; 40 kWh generally doesn’t span between locations. Most Superchargers are at natural road stops, with food service and bathrooms. Right now, that’s California (5 sites) and the East Coast (Delaware and Connecticut stops along I-95).
But… how can the company tackle infrastructure on its own? The long ranges of the Model S mean sites are much further apart than with CHAdeMO, and thus far fewer, while still forming a viable network. The long-term Tesla map claims that most of the country will be covered, with only 150-200 sites. In this scenario, sites are rural, so land is cheap, and it’s just a few parking spaces’ worth anyway. With no billing, no attendant is needed (though other networks have figured out electronic billing anyway).
But… but… how can charging be free? First off, free juice is a selling point, not just a bragging right. It sells more cars, and not the base 40-kWh model either. (Apparently it worked- people didn’t go for the 40 kWh, and Tesla dropped it.) Given low electric rates, Tesla can chalk up the rest as marketing and advertising. Tesla has spent hardly anything on traditional ads so far, and seems to be managing- apparently it worked.
Second, the Supercharger hardware actually fits Tesla’s business plan. Inside each Model S is one (or optionally two) 10-kW charging units- basically huge AC-DC converters. For external, DC fast charging, each Supercharger unit gangs ten of these on the curb. Each additional Supercharger installation, then, amortizes Tesla’s investment in the design and production of these converters. Each additional Model S, then, is slightly more profitable. This is the exact opposite of CHAdeMO, where the CHAdeMO specification only sets the interfaces. Details of charger construction were left to the market. ABB, AeroVironment, Eaton, Fuji, Siemens, etc. then devised and produce their own individual models, at multiple power levels, on individual lines, at lower rates and higher costs.
Third, rates for electricity are generally much lower than gasoline- as in 3x-5x lower. There is, however, an upcharge from the utility, for big loads at peak times. It’s equivalent to daytime overage charges on cell-phone plans, versus cheap or free evening and weekend minutes. Solar arrays are meant to combat this, both damping down spikes, and actually sending out power when no car’s hooked up. Selling solar power back to the grid (“net metering”) during daytime peaks may generate revenue.
A typical parking stall is 18×8 feet. As a sports sedan however, the Model S is very wide; owners notice their garages suddenly feel tight. Supercharger stalls thus appear to be larger than regular parking. The canopies also have a bit of overhang, and a slope leading to a 1/cosine increase in area. Depending on what you assume for area, one parking stall can then generate 10-15 kW. Superchargers at ~90 kW then break even at 11-18% utilization- i. e., someone’s there charging their Model S only ~1/7 of the time. Or you could think of it as six other stalls helping to power one stall. This analysis doesn’t work at night, of course, but night rates for electricity are lower, and there are no demand surcharges. If utilization falls below ~11%, the sale of solar electricity at day rates then makes the chargers short-term profitable. That’s right, a system may actually start making money. At minimum, the demand charges will be lowered.
So it’s about the utilization rate, then. Tesla is running this experiment right now: if site usage is light, cha-ching. If the rate exceeds ~18%, operations accrued must be swallowed as marketing and advertising. East-Coast operations certainly are, since there are no solar canopies.
At the Connecticut Superchargers, power is entirely from the grid. Connecticut is connected to the Vermont Yankee reactors for base load, and can also draw from Indian Point reactors and Canadian hydroelectricity in demand peaks. This is bulked out with coal as swing load, with the occasional natural-gas peaker. Ironically, Connecticut happens to be a place where the price structure favors solar, if not the weather. I’ll speculate that solar canopies will be considered, as installation costs continue to fall. At the Delaware Supercharger, the PJM portfolio (Pennsylvania-Jersey-Maryland) reflects the country as a whole: less than half coal, about a quarter nuclear plus hydro, with wind and natural gas ramping up strongly.
Tesla has just said expansion in California is imminent- more Harris Ranch chargers, as that site only had one unit. Within months, the company also claims “Pacific Northwest, Texas, Illinois, Florida,” in some sort. The exact sites haven’t been pre-announced, just like the CA and East Coast sites weren’t, either.
There you have it: a functioning EV network, all made possible by a 200-mile range, starting from existing home outlets. It’s not compatible with Nissans, but the Leaf can’t make the topology work out, either. Conversely, Tesla is building CHAdeMO-to-S adapters. Initial shipments will be for S owners in the Japanese sales territory, but you can bet they’ll show up on the grey market. When that happens, 45-, 25-, 20-, and 10-kW CHAdeMOs will add topology 4) Not-So-Superchargers.