Next Stop: Ultracapacitor Buses  

Technology Review has an article on buses using fast (and frequent) recharging ultracapacitors for energy storage (using existing technology rather than heavily promoted but possibly mythical examples like EEstor's device) - Next Stop: Ultracapacitor Buses.

Municipal transit agencies have tried to reduce the carbon footprint of their bus fleets using a range of options over the years, from biofuels and hydrogen to batteries and hybrid-electric diesel. Now a Chinese company and its U.S. partner say that ultracapacitors could offer the greenest and most economical way of powering inner-city buses.

There's just one catch: the best ultracapacitors can only store about 5 percent of the energy that lithium-ion batteries hold, limiting them to a couple of miles per charge. This makes them ineffective as an energy storage medium for passenger vehicles. But what ultracapacitors lack in range they make up in their ability to rapidly charge and discharge. So in vehicles that have to stop frequently and predictably as part of normal operation, energy storage based exclusively on ultracapacitors begins to make sense.

Sinautec Automobile Technologies, based in Arlington, VA, and its Chinese partner, Shanghai Aowei Technology Development Company, have spent the past three years demonstrating the approach with 17 municipal buses on the outskirts of Shanghai. On October 21, the two companies will offer a one-day demonstration at American University in Washington, DC, where an 11-seat minibus running on ultracapacitors will spend the day shuttling people around campus.

Electric vehicles can take hours to recharge, making cross-country road trips a challenge. But researchers at the Fraunhofer Institute for Chemical Technology in Germany say they've got a potential solution: flow batteries. ...

But here's the catch: one of the reasons hydrogen fuel cell vehicles have come under fire recently is that you need to install a large infrastructure for distributing and dispensing hydrogen. A flow battery system would have a similar problem. You'd need to install special refueling stations where the spend electrolytes can be recharged and dispensed.