June 12, 2012


A Tale of 2 Transit Systems: Battery-Powered Buses Enter the Mainstream  (Nick Chambers  | June 11, 2012, Scientific American)

Lithium ion batteries are still not energy dense enough hold more than the equivalent of between four and eight liters of gasoline in a battery package small enough to put on a bus. Nevertheless, inherent efficiencies in the electric drivetrain enable significant increases in fuel economy. Whereas a typical 12-meter-long, diesel-powered transit bus might return between one and two kilometers per liter, the electric ones that Foothill is running average the equivalent of 8.5 kpl. After some quick math it is apparent that 8.5 kpl combined with 7.5 liters of energy storage is not enough to fuel the hundreds of kilometers a bus might need to travel in a day. To get around this, both Foothill and LINK have added ultrafast charging stations in the middles of their buses' loops.

Foothill Transit operates three 12-meter long, 35-passenger buses built by Greenville, S.C.-based Proterra. Each relies on batteries that supply 72 kilowatt-hours and runs on a 27-kilometer-long loop that handles 5 percent of the yearly ridership. At specially built fast charging stations in the Pomona Transit Center the buses can fill up within 10 minutes on their normally scheduled layover, meaning they never have to travel more than 27 kilometers between full charges--about half what their rated battery capacity can provide. LINK's system is similar, although it uses five, Ebus-built, seven-meter long, 22-passenger trolleys with 28 kWh-batteries that travel on two separate eight-kilometer-long loops and can be filled in about seven minutes with a fast charge at the downtown Wenatchee Transit Center.

LINK originally planned to have its electric trolleys up and running by late 2010, but issues with the battery cooling system and manufacturing of the fast-charging station delayed full operation until later this year--although the trolleys are currently running for about two hours each day without fast charging. "There's nothing off-the-shelf about our trolleys," says Greg Pezoldt, special projects coordinator at LINK Transit. "As the first electric trolley of its kind, everything we have done with Ebus we've had to develop and sometimes redevelop. Even with the delays we're still excited about it, and we have an ultimate goal of electrifying the entirety of our Wenatchee and East Wenatchee routes."

It is no wonder LINK is still bullish on the endeavor: Pezoldt says a comparable diesel-powered trolley would cost about $435,000 and each electric trolley built by Downey, Calif.-based Ebus costs significantly less at $370,000. On top of that, diesel fuel for the same trolley on the same route runs about $1,200 per month, whereas the inexpensive and green hydropowered electricity used for the Ebus trolley comes in at approximately $100 per month--less than one tenth the cost. The biggest question revolves around battery life, but even with the worst-case estimates, Pezoldt says LINK still comes out significantly ahead with electric bus operation in terms of lifetime fuel and maintenance costs.

Posted by at June 12, 2012 5:55 AM

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