Hybrid technology has been around now for more than a decade, but as oil prices continue to rise and environmental pressures get stronger the market is growing and improving. Both the bus and rail sectors have seen advancements in technology that make hybrids more viable to transit agencies across North America.
One key to growing the market is volume and economies of scale, according to Mike Mekhiche, director of Products and Technology at BAE Systems. “I think the challenge is really the volumes. Economies of scale are really important to driving costs down and accelerating market acceptance of the product and technology in general,” he says. “We are at the point where, for example in the transit bus market, the volumes are sizeable, they are attractive, but they still are not high enough to get the costs down to where hybrid becomes the standard for transit bus propulsion systems. It’s kind of a chicken and an egg thing; you want volumes to reduce cost, but you want a lower cost to increase volume and so that’s a dilemma people like us and other hybrid suppliers are faced with and that is why continuous investment by companies such as ours is critical to sustaining and maintaining the technology as we build volumes to a point where the volumes will drive costs down. That’s the economic reality.”
On the bus side of the transit market, advances in batteries and ultra capacitors are making hybrid buses more appealing. In North America, the market for hybrid buses is gaining strength and growing. “We see the market and consider the market very important for us,” says Thomas Orberger, business manager for Siemen’s HybriDrive in the United States. “Right now, we see very aggressive development; I’m talking now about the bus market, from let’s say conventional systems, diesel systems into areas like the CNG parts, which is not necessarily the technology that we promote, and electric systems.”
Orberger says there is a strong interest in electric systems in the form of hybrid buses. “We’ve participated in development for a couple of years later actually but we see strong activity and strong acceptance and activity in this market,” he says.
Battery vs. UltraCapacitor
A big issue in hybrid bus systems is whether to go the battery route or the ultracapacitor route. “While both provide electric power, they have some fundamental differences. Both of them store energy, however, ultracapacitors store much less energy than a battery does when you look at per kilogram or per volume. But, what they do have is a much higher power density,” explains Chad Hall, vice president of sales and a co-founder at Ioxus.
Hall says no chemical reaction takes place when ultracapacitors charge and discharge, which gives them a long cycle life. Batteries, on the other hand, have what is called electroactive material and every time they are charged and discharged, the electroactive material begins to wear out. Therefore, the faster you charge and discharge a battery, the faster it will wear out.
“That’s the main difference; ultracapacitors are made to go millions of times, where batteries will typically cycle in the low thousands of times,” Hall explains. “There are batteries that are being used for buses, and they typically only use about 10 percent of the available energy in the battery pack so that they can do a high cycle life. There’s a ton of energy that’s wasted when they use a battery. With an ultracapacitor you discharge down to zero volts.”
Generally speaking, batteries require longer charge times. Ultracapacitors use breaking energy to recharge.
The upfront cost of ultracapacitors is slightly more expensive than if you were to use acid lead batteries, Hall says, but the price is closer when compared to lithium ion batteries when it comes to the number of modules vs. the number of cells. Both batteries and capacitors require some sort of management system — either a battery management system or a module balancing system for the capacitors — making the electronics similar for both options, according to Hall.