To Charge or to Swap: That is the Question for EVs

Last Updated Apr 27, 2010 12:49 PM EDT

TOKYO -- How long does it take to fill up a car with gas? Five minutes? That then, is the time electric carmakers would like fast charging to take. That is technically feasible, but practically difficult.

Better Place, a California-based global EV charging company, is pessimistic about fast charging. So it has developed instead a "battery swapping" plan that is at the heart of its network plans for Israel, Australia, Denmark, Canada and parts of the U.S. At a battery forum in Tokyo, where the company has just rolled out its first swapping station, for a trio of Nissan taxis, Kiyotaka Fujii, president of a Better Place Japan, explained the company's thinking.

 The [switchable-battery electric taxis] taxis developed for this demonstration are able to drive through our battery switch station, exchanging a depleted battery for a fully charged one in less time than it takes to fill a tank with fuel. This allows the EVs to run continuously, which is an absolute necessity for taxis.

As of today, we have switchable-battery electric taxis transporting passengers in Tokyo. This is a major accomplishment in terms of promoting environmental sustainability, but it also demonstrates how electric taxis can be made economical (and, therefore, sustainable) in the long run.

The debate about fast-charging is not new. As early as 1998, General Motors and Southern California Edison showed off a 50-kilowatt-hour quick-charge station that could refuel an electric Chevrolet S-1- or its EV-1 from near-empty to almost full in 12 minutes. But that charger required heavy-duty wiring not only in the car but in the grid, too, and it was never put into regular use by the GM EV program.

The general assumption is that big-box stores such as Best Buy, Home Depot and others will offer fast charging in their parking lots, maybe even free, because it will attract consumers who will shop while they're waiting for their cars to recharge. But a quick and informal survey revealed that none of the major chains appears to be gearing up for such a plan.

Better Place is dismissive about the prospects for five-minute charging. According to Michal Vakrat Wolkin, the company's director of energy storage technologies, "With five-minute quick charging the battery pack will be heated up, destroying the life of the batteries. Another problem is the capacity of the grid--if you're using 300 kilowatt hours of electricity for each car, just two vehicles is the equivalent draw of an office building. We believe that swapping is a better choice because whether the recharging of your pack takes five minutes or eight hours, it doesn't really matter because you swapped batteries in less than a minute."

Evan Thornley, CEO of Better Place Australia, said that quick-charging sessions would likely cluster in the late afternoon or early evening--"at the worst possible time for the grid. The average substation is just two to four megawatts, so just seven cars using 300-kilowatt-hours would take over the electricity for a whole suburb. And there are safety problems holding wires with that amount of juice running through them--I wouldn't want my kids, or me for that matter, handling plugs like that."

The HSBC Group believes in the company's battery-swapping model; the bank just raised $350 million in equity financing for Better Place. According to Mark Norbury, associate director of principal investments at HSBC, "We couldn't find any expert to say that five-minute fast charging is feasible. The grid and the government can't allow it to happen. Imagine millions of cars--the equivalent of millions of office buildings--switching on and off every five minutes."

Still, some car and battery makers say very fast charging is feasible. Altair Nanotechnologies said in 2007 that its 35-kilowatt-hour nanotech-enhanced lithium-ion packs have unusually stable chemistry that can fast-charge in 10 minutes without harm.

And according to Jonathan Read, CEO of the ECOtality charging network (partnered with Nissan on the Leaf introductions), "It takes 10 to 15 minutes to fast charge, which isn't going to be much quicker or slower than swapping a battery, and certainly a lot less moving parts and potential points of failure."

This is, in fact, the key point of contention: Better Place says that very fast fill-ups will never be feasible, and charging companies like ECOtality say it will.

The California Air Resources Board has set a goal of an 80 percent charge in 10 minutes, and proponents say that while it may never be feasible for consumers to handle that amount of current at home, it can work in public places such as those big-box store parking lots. Utilities (which really like electric cars because of the new revenue streams they will provide) have so far been supportive of such charging schemes in principle, but it's not clear they are preparing for the additional mega-loads they would represent.

Photos: Jim Motavalli (top), General Motors