One of Tesla Motors' key selling points is its Supercharger network, a system of publicly-accessible, high-power electric vehicle rechargers that can juice up Tesla models to an 80 percent charge (around 170 miles of range) in about 30 minutes. Perhaps as important: It’s free.

The Superchargers are located along key Interstate highway corridors, often in rest areas with chain restaurants, so that owners can grab a bite while their Tesla is recharging. The proprietary charging port only works on Tesla vehicles.

Tesla plans to double the size of the Supercharger network by the time the more affordable, higher-volume Model 3 arrives in showrooms at the end of 2017. The Model 3’s price will range from $35,000 to near $60,000, with an annual U.S. sales target of around 200,000 vehicles. That means if all goes according to the sales plan, by 2020 there will be nearly 1 million Teslas on the road. Can the Supercharger network keep up?

Tesla has said Superchargers are meant for vacation-style road-tripping, not as a replacement for an in-home charger for the daily commute. But the lure of a free, quick recharge has been strong for many, which has already led to frustrating wait times at key locations. Last Christmas, a photo circulated on social media showed a half-dozen cars lined up at the Tejon Ranch station in California, with owners reporting more than a dozen cars waiting.

Some would argue that this was an extreme case—a busy route on a holiday weekend—but it shows the potential problem when vehicle supply outstrips electrical demand.

Let’s do the math: Currently, there are 1,725 Tesla Supercharger outlets in the U.S. for 66,000 Teslas in operation—that's a single outlet for every 38 Teslas. If the company does manage to double its Supercharger network by the time the Model 3 arrives, that will bring the number to around 3,500 outlets.

But even if Tesla decided to keep up that pace of Supercharger expansion and build another 1,800 Supercharging outlets every year between now and the end of 2020, the result would be about 10,725 outlets for about 1 million Teslas on the road. That works out to 1 outlet for every 93 cars, more than doubling the current cars-to-chargers ratio.

However, that projected math is too optimistic, says Brad Erickson, a market analyst who tracks Tesla for Pacific Crest Securities.

Erickson expects “the pace of Supercharger additions to slow toward the end of decade,” because Tesla believes the vast majority of charging will occur at Tesla owners’ homes. Tesla’s rationale: Most commutes or city trips are 30 miles or less. There’s no need for tens of thousands of Superchargers.

By contrast, “there are 160,000 gas stations in the US. The use case behind gas-powered cars is strong because gas stations are everywhere,” Erickson said. “Tesla’s view is that people’s usage and charging patterns need to change, and will change.”

In other words, Tesla may get to 3,500 Supercharger outlets, and slow down or stop that rollout. If there are 1 million Teslas in 2020, and 3,500 outlets, that's one outlet for every 286 Teslas. And every year after 2020, should sales continue to roll out per Musk's projections, another 250,000 new Teslas will hit America's roads—placing that much more demand on the Supercharger network.

Tesla Model S at Supercharger
Tesla Model S at Supercharger

Waiting Lines

At Tesla’s launch of the Model 3, Tesla CEO Elon Musk talked about the importance of quick charging: “[Supercharging] gives you freedom of travel. It means you can conveniently go when you want, where you want, and how you want . . . a lot about having a car is about freedom, about going where you want to go, and Superchargers are critical to that.”

But Tesla's Supercharger network already has shown signs of strain. A handful of Supercharger stations in key locations are already experiencing waiting lines, according to Tesla owner forums. Unlike owners of gas-powered cars, Tesla drivers seeing a low-charge indicator don’t have the option of driving down the road to a less-crowded station.

Wait times can become excessive during peak periods such as Friday afternoons and busy travel holidays—times when a Tesla owner might want to top up for a trip without having to wait for a two-to-four hour recharge at home. Three cars ahead of you in line at a Supercharger? You could be twiddling your thumbs for a while waiting to continue your trip.

The problem is not limited to the US: Last year, the Wall Street Journal reported on a Tesla owner in the Netherlands who doesn’t even try to use his local Supercharger station, since Tesla taxicabs take up most of the spots.

“Topping off” is part of the problem: Quick chargers must reduce the velocity of current delivered as the battery fills. While the Supercharger can charge a Tesla from 10 to 80 percent in around 30 minutes, it can take an additional 35 minutes to charge the battery from 80 to 100 percent. That could mean an hour-plus waiting time behind someone who wants a completely full charge.

Also, each Supercharger port supplies two outlets, and when both outlets are in use the charging slows down. (One forum member reported taking 90 minutes to fully charge his car.)

Already, there are blogs in the EV community about the etiquette of EV charging when others are waiting—and squabbles have erupted from those waiting behind people wanting to top off. Tesla itself started a furor among owners in 2015 when it sent a chiding letter to those who—in Tesla’s opinion—too frequently availed themselves of the Supercharger network.

At this stage of the automaker’s evolution, the vast majority of Tesla owners are enthusiastic early adopters, and view the occasional recharging wait time as a minor inconvenience. When we contacted several Tesla owners who had complained about the issue in online forums, they declined to be interviewed or responded with unwavering support for Tesla. But when Tesla’s idea of electric vehicles grows, the mass market might not be so willing to endure such inconveniences.

Tesla also is rolling out “destination charging” ports at select hotels, restaurants, and the like. But these are not Superchargers—most require three to four hours to fully charge a vehicle.

Competing Technologies

EV manufacturers are betting on ramping up quick-charging technology, which intends to find a way around the problem of “pushing electrons” more quickly into the battery pack.

Tesla’s Supercharger is not the only quick-charging system available, though with the ability to deliver 120 kilowatts, it is the most powerful.

Among other quick-charging technologies—though not as fast as a Supercharger—the Department of Energy says there are 1,085 “CHAdeMO” stations with 1,489 outlets, and 580 “SAE Combo” stations with 886 outlets.

The SAE Combo system, used primarily by American and German EVs such as the Chevrolet Spark EV, BMW i3, and Volkswagen e-Golf, maxes out at 100 kW of power, while the CHAdeMO system used by Asian EVs such as the Nissan Leaf, Kia Soul EV, and Mitsubishi i-MiEV, delivers 62.5 kW. Generally speaking, cars built for one type of quick charger are incompatible with others, though Tesla does sell a $350 adapter for CHAdeMO chargers, and has filed a patent for an adaptor the would support both CHAdeMO and SAE Combo plugs.

One can understand why Tesla would develop their own standard: With higher-capacity batteries than most EVs, Teslas need higher power levels for a quick charge that is truly quick. A 62.5 kW CHAdeMO charger hooked up to a Tesla Model X simply can’t pump juice as quickly as a 120 kW Supercharger at full tilt.

Tesla Model 3 front and rear
Tesla Model 3

Temporary Measures

Tesla has started to address the issue of overcrowded California stations by implementing peak-time staffing. Tesla says their attendants’ role is to “manage onsite customer demand and feedback,” and emphasizes that they will not serve as valets who would take keys or move vehicles.

However, because Tesla often places Superchargers near places where people can eat, rather than just stand around, there have been online spats about those who park the car at a Supercharger, then eat a leisurely dinner even though the car may reach a full charge during the meal.

Tesla also plans to update the navigation software in existing cars to show the number of available charge ports at Supercharger stations, though they have not said whether they will share this information with third-party apps such as PlugShare. It is unknown if Tesla has the capability to show how many cars are waiting in line at stations that are fully occupied.

If Tesla meets its sales goals, the Supercharger network may be the victim of the car’s success. Wait times could get longer. Having a navigation system that knows how many Supercharger ports are available or an attendant to shoo you away at 80 percent charge will not solve the looming clog. Tesla could look at implementing a reservation system for Supercharging, but that could compromise the sense of freedom that Musk described at the Model 3 launch. And Tesla is banking on Supercharging for long-distance travel, having all but ditched plans for its proposed battery-swapping stations.

One hope for expanding the Supercharger network may be that third-party companies will start building Tesla-compatible quick chargers, perhaps for installation at gasoline fuelling stations. Tesla has, after all, made its patents available to the world. But a third-party charging station would likely want to make money on its investment—hence conflicting with Elon Musk’s pledge that Superchargers would be “free forever” for Tesla owners.

The slow rollout of solar-powered stations may be another sign the Supercharger network may not be able to ramp up as quickly as hoped. In 2013, Musk talked about having something on the order of 200 solar-powered Supercharger stations in the near future. Musk’s holdings in panel-maker Solar City would make it happen quickly, he said. But the first solar station did not open until 2015, and so far only two more have followed. The rest of the stations pull power from the grid.

When asked about solar-powered stations in place today, Tesla won’t commit to a number. “While we continue to build out our charging network,” a Tesla representative told Consumer Reports, “we will pursue these renewable resources as much as we can in territories where it makes the most sense.”

For now, Tesla owners should enjoy the peace and quiet at Supercharger stations. If all goes as planned, it may not last long.