Future Prius bumper sticker: My other hybrid is a city bus

Hybrid and electric passenger cars have been getting a lot of attention lately since the announcement by GM that it was working on the electric-hybrid Chevy Volt. But there’s a huge market in industrial and commercial vehicles for hybrid-electric designs, because of the constant acceleration and deceleration many of these vehicles have to support. For example, according to Bobby Maher, Director of Business Development at Maxwell Technologies, the average speed of a city bus is 12 mph – and in New York city, it’s just 6 mph. City buses and delivery vehicles spend much of their time starting and stopping, and anyone who’s been stuck behind one in city traffic knows they are often serious polluters. Hybrids are poised to take off for transportation, delivery, and industrial in a big way because, Maher says, the government will subsidize hybrid vehicles for buses in order to reduce metropolitan area pollution. New York City already has about 500 buses running with a lead acid battery-based hybrid design.

Batteries, especially lithium ion, make a lot of sense for purely electric vehicles, but they have some drawbacks for hybrids. They are heavy, expensive, and have a limited life based on their charge/discharge cycles. And hybrids are all about charging and discharging.

Maxwell Technologies just introduced a new ultracapacitor module, the HTM390, which aims directly at the sweet spot ofheavy-duty transportation and industrial systems. The 390V ultracap has a virtually unlimited number of charge/discharge cycles and can discharge down to essentially 0V, a problem for many battery types. It has a peak current capability of 950A, and a continuous current capability of 200A, or 265A at a 33% duty cycle.

Ultracaps are excellent at providing power, but not so good at storing energy and holding it, which can be a factor for a bus or delivery vehicle that can sit unused in a parking lot for a week at a time. The HTM390 addresses this with a self-discharge rate (also called leakage rate for batteries) of 50% in 30 days. The overall energy specs are 282 Wh and 1.71 Wh/kg. Pricing is in high volume is lower than $10/kW.