The ProterraEcoRide BE35 is a 35 foot (11 m) (nominal length) fast-charge battery electric bus that seats 38 (including the driver) with a total passenger capacity of 60 in its composite low floor body. Foothill Transit was the first transit agency to operate the buses in revenue service, starting in September 2010.[3][4] It is the first 30 ft (9 m) or larger, heavy-duty all-electric bus ever to complete federally required durability, reliability and safety testing at the Bus Research and Testing Center in Altoona, Pennsylvania. The 12yr/500,000 mi (800,000 km) STURAA test was completed on March 5, 2012.[1]
The BE35's electric traction motor draws from lithium-titanate batteries supplied by Altairnano that can be recharged in 5–10 minutes while stopped at a bus stop via overhead terminals connected to a charging station, without driver involvement.[5] The quick charging during a brief layover typically enables a further 26 miles (42 km) of operation.[6][7]
CEO Dale Hill and VP Phil Sweesy of Mobile Energy Solutions, LLC (MES) in Golden, Colorado had previously designed, engineered, and manufactured the 36 CNG-fueled TransTeq EcoMark I hybrid buses for the 16th Street Mall in Denver, Colorado.[8][9][10][11] In 2006, MES announced it was designing a battery-electric bus codenamed "Origin One", recharged by onboard hydrogen fuel cells; the company announced it had already won a contract for two buses from the Greater New Haven Transit District, the transit agency serving New Haven, Connecticut.[12] This was followed by a 2007 contract for two more fuel cell buses for Burbank, California; by this time the key characteristics were announced: a 35-foot (11 m) composite body provided by Martin Marietta, lithium-titanate batteries, and plug-in charging in addition to onboard charging through the use of a range-extending auxiliary power unit (APU) consisting of two 16 kW fuel cells from Hydrogenics.[13]
Developmental funding was provided by the Federal Transit Administration (FTA), who had awarded a grant under the National Fuel Cell Bus Program to a team led by the Center for Transportation and the Environment (CTE); CTE had selected MES to develop the prototype bus.[14] MES was also a partner in the FTA's Electric Drive Strategic Plan program.[15] MES acquired an old school bus to serve as a mobile development laboratory (MDL) for drivetrain development, including the battery, traction motor, and control system. The MDL was damaged after one battery cell leaked electrolyte, short-circuited, and caught on fire, leading MES to redesign its battery management system and add a protective enclosure for the battery modules in the finished prototype.[16]: 15
MES changed its name to Proterra in June 2008[17] and exhibited a prototype of the HFC35 transit bus that October at the American Public Transit Association Expo in San Diego.[18]: 34 As shown with the fuel cell APU, Proterra claimed the HFC35 had a range of 250 miles (400 km) before needing to be refueled or recharged.[15] Alternatively, the HFC35 could be optioned with diesel, gasoline, or natural gas APUs.[19]
In 2009, Proterra demonstrated a variant of the HFC35 that omitted the APU altogether,[20] which Proterra named the EcoRide BE35.[21] The BE35 stopped in four California cities during its weeklong tour: San Jose, Los Angeles, Sacramento, and San Francisco.[22][23]
Deployment
TARC EcoRide BE35, docked in overhead charger (2015)
Proterra introduced the 40-foot (12 m) Catalyst in 2014, featuring a longer range and new fast-charging system.[39]
Design
Proterra drew inspiration from existing and prototype composite buses: the Neoplan USA Metroliner in Carbon [de], Advanced Technology Transit Bus (ATTB), and NABICompoBus, concluding that a composite bus body was best suited to reduce weight and accommodate an equivalent number of seats (37) as a conventional 40-foot (12 m) low-floor transit bus. The composite body forms were finished by Pearson Composites in Warren, Rhode Island, and the shells were assembled by C&C Fiberglass Components using vacuum-assisted resin transfer molding.[14] Some of the people who helped develop ATTB would go on to work for MES.[15]
Although the batteries can be recharged quickly, the overall capacity is low. The BE35 and HFC35 shared the same electric powertrain and battery design;[16] while the HFC35 had a range-extending APU, no additional battery storage capacity was added to the BE35. The battery pack has a total storage capacity of 54 to 72 kW-hr,[40] composed of three or four 18 kW-hr battery strings. Each string weighs 550 pounds (250 kg).[41] A single string is built from sixteen modules wired in series, each rated at 50 A-hr and 23 volts; the total string is 368 volts and 18.4 kW-hr, and three or four strings are used in parallel for the overall capacity of 54 or 72 kW-hr.[42]: 12 However, using on-route fast charging, an EcoRide BE35 set a record in April 2014 by driving more than 700 miles (1,100 km) in 24 hours.[43][44] In June 2016, Proterra announced it would grant royalty-free access to the patents covering their FastFill overhead charging system.[45]
Proterra uses the TerraVolt branding for the battery system and ProDrive for the drivetrain module, which includes the traction motor and optional range-extending APU.[46][47] The traction motor announced with the HFC35 and the first versions of the EcoRide BE35 was supplied by UQM Technologies and branded PowerPhase 150,[19] offering a peak and continuous power output of 150 and 100 kW (200 and 130 hp), and peak and continuous torque of 650 and 400 N⋅m (480 and 300 ft⋅lb), respectively.[48] The traction motor was upgraded to the UQM PowerPhase HD220 in 2013, which increases peak power and torque to 220 kW (300 hp) and 700 N⋅m (520 ft⋅lb), respectively.[49]
Testing
The first HFC35 prototype was not available for service for approximately two months to address a failure in a DC-DC converter, which provided the interface between the fuel cell APU and the traction battery.[16]: 21
Results from the BE35 STURAA test showed an average, combined fuel economy of 1.81 kWh/mi (1.12 kW⋅h/km) or 20.84 miles per US gallon (11.29 L/100 km) diesel equivalent.[2]: 39 Compared to the buses it replaces—conventional diesel buses average 3.86 miles per US gallon (60.9 L/100 km); CNG buses return 3.27 miles per US gallon (72 L/100 km) diesel equivalent; and diesel-hybrid buses average about 4.6 miles per US gallon (51 L/100 km)[50]—the results are up to 600% better. During 15,000 miles (24,000 km) of testing at Altoona for the first BE35, unscheduled maintenance included the replacement of the transmission (twice) and the traction motor (once).[1]: 86–90
Foothill Transit has been working with the California Air Resources Board and the United States Department of EnergyNational Renewable Energy Laboratory (NREL) to study the real-world performance of its Proterra buses.[51][52][53] Observed economy for twelve BE35 buses in the Foothill Transit fleet was 17.24 miles per US gallon (13.64 L/100 km) diesel equivalent, compared to an observed 4.15 miles per US gallon (56.7 L/100 km) diesel equivalent for a fleet of eight NABI42-BRTCNG-fueled buses. However, the BE35 fleet operates on circulator routes at slower speeds compared to the NABI CNG fleet, which were dispatched as needed to any Foothill Transit route. The BE35 fleet achieved an availability of 80.6%, less than the desired 85% availability due to constraints on parts availability and low-voltage battery (i.e., not the propulsion batteries) reliability; the NABI CNG fleet achieved an availability of 96.8%. Total maintenance costs for the BE35 fleet ($0.41/mi) is also higher than the maintenance cost for the NABI CNG fleet ($0.27/mi).[53]
^Argonne GREET model 2012, assuming 36,000 mi (58,000 km) per year and fuel consumption of 3.86 miles per US gallon (60.9 L/100 km) diesel and 3.27 miles per US gallon (72 L/100 km) diesel equivalent for CNG.
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