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Sustainable Energy

Why Tesla Thinks It Can Make Battery Swapping Work

Tesla is set to announce a way to make recharging its electric vehicles faster than filling up a gas tank.

Limited battery range is a barrier to widespread adoption of cleaner electric cars.

Tomorrow Tesla Motors will announce a way to charge its Model S electric vehicle faster than a conventional car’s gas tank can be filled—by swapping a depleted battery for a fully charged one.

tesla at a charging station
Fill ‘er up: A Tesla Model S is shown here at a Tesla Supercharger station.

Such a system would address one of the big drawbacks of electric cars: limited battery range and slow recharging make them poorly suited to longer road trips. But there are questions about how practical it would be, especially as a way to help make electric vehicles more popular.

It currently takes about 30 minutes to charge a Tesla’s battery halfway at one of the company’s supercharging stations, where Tesla’s cars can be charged more quickly than normal. A full charge at home from a common 240-volt outlet would take the better part of a day, although a high-power wall connector can cut that to about five hours.

The battery-swapping approach has a bad reputation: Better Place, which built a business on that model, recently filed for liquidation after failing to get enough customers (see “How Better Place Came to a Bitter End”).

But swap stations might make more sense for Tesla. That’s because they wouldn’t be the core of the company as they were for Better Place, just a way to win some more customers for a car that people are already buying (see “Tesla’s Superchargers Matter Only Because It Already Sells a Car People Want”).

Better Place sold a charging subscription service aimed at overcoming the range limitation of one specific car, the Renault Fluence ZE, which could go about 100 miles on a charge. Without an adequate network of swap stations, the service wouldn’t work. So Better Place had to install, at significant expense, 37 stations (for its first market, Israel) before it started selling its service at a large scale. Tesla could start with just one swap station and build more if the approach seems successful.

There are still questions about how battery swapping would work in Tesla’s case. In the Better Place model, customers didn’t own the battery, so it didn’t matter if they received a new or an old one; the company would just guarantee a minimum capacity. In Tesla’s case, customers do own the battery and won’t want to replace it with an older one that has a lower range and value. So the company may just let people borrow a battery and pick up the original one on a return trip.

Swapping stations may be installed at Tesla’s existing and planned supercharging stations, at which solar panels will help charge batteries. The stations will already have extra batteries on hand to store energy from the solar panels, and those could be swapped for drivers’ drained batteries.

For Tesla, the swap station would be a service attached to a high-end product, but it’s debatable whether battery swapping is the best strategy for more mainstream electric vehicles. For them, cost becomes a bigger consideration. And making a swap station to serve one vehicle is much easier than making one to serve a wide variety of vehicles with different batteries.

“I think that battery swapping could work, but individual companies will have to take the lead,” says Andrea James, an analyst for Dougherty & Company. “Nobody wants to share their battery [intellectual property] to come up with a standardized battery.”

There may be other options for making electric vehicles better suited to distance driving and more convenient in general. For example, BMW says it may offer a service package with its upcoming electric cars that would give its customers a gas-powered car for a certain number of trips.

Some researchers have even proposed installing wireless chargers in roads (see “Charge Your Phone (and Your Car) from Afar”). While batteries are likely to vary from vehicle to vehicle—different vehicles will have different requirements for shape and capacity—the wireless receivers could be standardized.

Meanwhile, ABB is demonstrating a “flash-charging” system for transit buses in Geneva, Switzerland. A robot arm at the top of the bus plugs into a charging station at every third or fourth bus stop along a route, and an ultracapacitor delivers 400 kilowatts of power for 15 seconds, providing enough power to get to the next flash charger.

For now, though, charging at home—and possibly at work—will make it easy enough to keep an electric car ready for daily driving. Indeed, one of Tesla’s rivals, GM, is focusing on developing charging stations for home and work to support its electric vehicles (see “Will Fast Charging Make Electric Vehicles Practical?”).

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