About five years ago BAE Systems transitioned from a lead acid battery in their systems to a lithium ion technology-based battery system. According to Mekhiche, the lithium ion-based system is a higher energy density technology, which means the weight of the battery itself is a lot lower, resulting in additional fuel savings. “It also supports longer range EV, electric vehicle, operation, shutting the engine off that is. We also introduced or looked at how the electric machine technology evolved. We see a lot more use of current magnet technology-based machines. Current magnet technology-based machines do give you higher efficiency than their counterpart, for example induction motors, they give you a lower weight and they’re easier to cool, and therefore they are simpler to integrate within the vehicle itself. That’s another trend with the technology itself,” he says.
While hybrid technology for buses continues to evolve and gain popularity, Orberger says hybrids are just a jumping point to full electric.
“We see the hybrids as this common understanding the hybrid platform is just a transitional technology to all electric transmission in the vehicles. What we’ve done at Siemens, we have always, at the end of the tunnel at the end of the horizon for Siemens, is an all-electric transmission for personal vehicles as well as bus, is the ultimate goal and we see the market is developing,” Orberger says.
On the rail side of the transit industry, there are a couple of different ways to look at hybrid technology. In some instances it could mean going from online catenary power to offline power using ultracapacitors or an in-ground energy source, a technology that Alstom Transport has demonstrated. Hybrid rail can also be more of a dual-power technology, using a diesel engine for part of the trip and then hooking up with electric power via catenary down the line, as Bombardier has demonstrated.
Alstom Transport has had an offline service for nearly 10 years in place in Bordeaux called APS, which drove Alstom’s off-wire developments. “That was specifically developed because the city of Bordeaux has an important historical city center they wanted to preserve so there were broad stretches of alignment where they were requiring no wires, which meant we had to go to a full autonomy solution, basically a full wireless solution,” explains Guilillame Mehlman, Alstom Transport managing director. “That meets a particular need which is preservation and aesthetics in historical city centers where you’ve got to achieve basically a mile, more than a mile or more sometimes the full alignment without relying on catenary power.”
While APS is not hybrid in the sense that it still draws power through the ground from the third rail in the middle of the alignment, it is a full off-wire solution, Mehlman explains.
“It’s a very specific solution we’ve developed and as for all the partial autonomy, full autonomy or hybrid propulsion, there is an extra cost as compared to a traditional catenary-powered LRV system,” Mehlman says.
Alstom has also developed super capacitor solutions that provided limited stretches of partial autonomy. This solution is ideal for areas that are difficult to get across because of complicated intersections or elevated structures where the relocation of utilities or the existing environment doesn’t lend itself to the installation of a catenary system.
“So to get across these special areas of typically less than a quarter of a mile, there we’ve got a super cap solution that’s called EchoPack and that’s typically a few kilowatt hours of power stored and that meets a different kind of need, very limited stretches without relying on the wire,” says Mehlman.
Taking a more traditional hybrid approach, Alstom is developing a solution that blends an APS solution with no wires with a small super cap solution that would be able to recover breaking energy, which is something the APS solution can’t do.
“If you have a super capacitor on the vehicle you can recover braking energy from the vehicle itself and re-inject it back into the same vehicle again when it starts, when it’s accelerating,” explains Mehlman. “So that is both an off-wire capability and a full-braking energy recovery system so that’s a hybrid solution that we’re developing and that we’re promoting because it’s basically greener, more sustainable at a slight extra cost; you’re reusing all the recoverable energy that you can. That’s something we’re pushing but haven’t yet contracted. A recent development, and it’s kind of a hybrid solution that we have developed.”
Batteries are another option. “Batteries are an interesting animal; they kind of handle the middle range,” Mehlman says.