Foothill Transit Battery Electric Bus Demonstration Results

Proterra battery-electric buses in service in a 12- vehicle demonstration by Foothill Transit in California offered significant fuel savings compared to similar conventional vehicles, according to a recently published analysis of the results of the demonstration by the National Renewable Energy Laboratory (NREL). 
The NREL team found, inter alia, that the battery-electric buses (BEBs)had an overall average efficiency of 2.15 kWh per mile on the service route, which equated to 17.48 miles per diesel gallon equivalent (DGE). The baseline CNG buses had an average fuel economy of 4.04 miles per gasoline gallon equivalent (GGE), which equates to 4.51 miles per DGE. These results indicated that the BEBs have an average fuel economy that is nearly 4 times higher than that of the CNG buses.
The NREL team also found that reliability, measured as miles between roadcalls (MBRC), was high during the data period (April 2014 through July 2015). The overall bus MBRC for the BEB fleet was more than 9,000. During the data period, there were only three roadcalls that were attributed to issues with the battery system, the primary power system for the buses.
This resulted in an ESS-related MBRC of more than 133,000. The NREL team called this “exceptional for an advanced technology bus in the early stage of commercialization.” The CNG baseline buses achieved an overall bus MBRC that was more than 45,000, which is expected of a new, fully commercial product.
Other findings included:

The average energy efficiency was 2.15 kWh per mile over 399,663 miles of use.

The average battery pack SOC is 75.4%, indicating a possibility for a usage window shift.

The average runtime per day is 13.2 hours with an average of 13 charges per day. Each charge averages 20 kWh energy delivered.

Accessory loads contribute to the overall range capability, as more than 50% of “system on” time is spent at a speed of 0 mph where lighting and HVAC loads are still required.