Why Ultracapacitors Will Be Your Hybrid's New Best Friend

A good 15 years ago, Honda invited me to travel to its engineering center and proving grounds in Japan to preview a boatload of future products, including stuff like the first four-stroke chain saws, string trimmers and lawnmowers. Then I had the chance to check out a dynamometer room with an ultra-low pollution environment. This chamber was where they tested the next generation of cars-the ones we're driving around now, labeled Super Ultra Low Emission Vehicles (SULEV). Yeah, I think its goofy nomenclature too. Anyway, the room was hypersensitive to hydrocarbons-so sensitive that engineers found the paint on the car bodies and lubricants in the chassis and doorjambs represented a substantial amount of the pollution they were measuring. Eventually, I was told, they had to resort to bare-metal car bodies to eliminate all those false positives.

All of this was incredibly interesting, but the one thing that genuinely impressed me was the hybrid car they let me drive around the proving grounds for a half-hour or so. It was basically a tiny little Japanese domestic market cutter way too small to market in the States. I mean, it was barely bigger than a Smart Car, which, of course, they just started selling here this year. I guess times have changed. Anyway, this little tyke was powered by a 1-liter engine, and it was bog-slow. It was really too slow to be on U.S. Roads-easily slower than my old 1200-cc VW microbus, anyway. Heck, I should have had an hourglass on the dash in place of that speedometer.

But then the engineer sitting next to me toggled a switch, and the thing changed its character immediately. Acceleration was on a par with any four-banger economy cars we drive today. The boost of power came from the hybrid system he turned on, a prototype of what eventually developed into the Intelligent Honda Motor Assist (IMA) that we can buy today. It was a simple "mild" hybrid system that used a flywheel-replacing generator to convert the vehicle's kinetic energy to electricity, which was stored and routed back to the flywheel, which was then used as a motor to convert the electricity back to Forward motion. This not only improved the acceleration from that tiny engine, it improved fuel economy, too.

All of that is old hat, as you know-except for the fact that the thing did not have a battery for storing any of that 7.5 kilowatts of energy (enough to hit 0 to 50 mph three times at full throttle). Instead, it had an "ultracapacitor" under the rear seat-a metal box about the size of a violin case. At the time, Honda engineers saw the ultracapacitor as the system they would use when the IMA went into production a few years later. But like many engineering prototypes, the cost targets were never realized, and the system that ultimately went into production was battery-based.

Will nanowire based ultracapacitors ultimately wind up in hybrids? Quite possibly-we saw some stunning developments this week at MIT. The power density of batteries is superior right now, and the cost of batteries is constantly edging down. Here's what I predict: If ultracapacitors can be made successfully at a competitive price point, conventional hybrids will transition from batteries to ultracapacitors because of the capacitor's longer life span and lower internal resistance, as well as its deep-discharge tolerance. While a battery pack can be damaged by being discharged completely, capacitors simply do not care.

Plug-in hybrids, on the other hand, will still likely use batteries for their main battery pack, and capacitors for reclaiming energy while slowing down and to provide high-current acceleration. This will let the battery discharge and recharge at moderate current, which should offer better performance and battery life over the long haul. Get ready for these ultracapacitors, because I think they're on the way.