Electric Bus Uses Rooftop Automated Fast Charging

By · May 23, 2013

Check out the clever automated rooftop charging system in action.

Two all-electric buses began trolling the streets in Stockton, in central California’s San Joaquin Valley, on March 20.

The electric buses in Stockton recharge in 10 minutes using an automated rooftop recharger. The bus pulls under the charging unit. After it’s lowered on to the bus, the conductive charge is added at 500 kilowatts, and the bus rolls away with an additional 20 or so miles of range in its 72 kilowatt-hour battery pack—well beyond the range of a typical bus route.

Passengers can load and unload, and he driver can stay in the bus, during the recharging event. And the electric refueling is essentially an “opportunity charge” because the buses return to the same place on the route, and usually are idle for about 20 minutes—before the bus begins a new route. (There must be similar scenarios for certain types of electric cars that have common routes.)

The connection and controls of were developed by Proterra. Eaton built the chargers used in Stockton, but Proterra has worked with other companies as well, said Marc Gottschalk, Proterra’s chief business development officer.

The 35-foot buses, manufactured by Proterra, are the first pure electric transit buses in Northern California. But Proterra, based in Greenville, South Carolina, also has electric buses running in Pomona, Calif. and San Antonio, Tex. It has orders for between four and six buses from Worcester, Mass., Seneca, S. Car., and Reno, Nev., said Gottschalk, in an interview with PluginCars.com.

Right-Sizing the Battery

“We fit the battery to the application,” Gottschalk said. A transit bus route is typically between 11 and 15 miles, Gottschalk explained. So a charge range would likely be around 20 miles to leave a margin of safety. Sizing the battery to fit the route saves customers money, he said. “Batteries don’t last forever,” said Gottschalk. So building to fit the need also keeps replacement costs at a minimum.

Proterra electric bus

Proterra’s buses run on a powertrain developed by the company itself, said Gottschalk. They use a lithium-titanate, or L.T.O., battery produced by Altairnano of Reno, Nev. L.T.O. batteries are less energy-dense and heavier than some other batteries, he said. “The L.T.O. advantage is you can fast charge and they don’t heat up and they don’t degrade as quickly” as other battery chemistries, he said. “They are great for fast charging.”

“We have been pushing the envelope here at the Regional Transit District in adoption of new technology for the last nine years or so,” Paul Rapp, marketing and communications manager for the San Joaquin Regional Transit District (RTD) told PluginCars.com.

The RTD’s 73-bus fleet will become 100 percent diesel-electric hybrid next month, he said. But the Proterra buses are the first all-electric the RTD has tested, said Rapp. The vehicles’ zero emission feature is especially attractive because the San Joaquin Valley does not meet the federal or state government standards for the level of ozone and particulate matter, according to Rapp.

Stockton, located in the San Joaquin Valley, used a $2.56 million grant from the California Energy Commission to pay for part of the $4 million electric bus demo project. After two years, Stockton will keep the buses.

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