A battery electric bus is an electric bus that is driven by an electric motor and obtains energy from on-board batteries. Many trolleybuses use batteries as an auxiliary or emergency power source.
In 2018, the National Renewable Energy Laboratory (NREL) found that total operating costs per mile of an electric bus fleet and a diesel bus fleet in the United States are about equal.
The London Electrobus Company started running the first ever service of battery-electric buses between London's Victoria station and Liverpool Street on 15 July 1907. However, the weight and inefficiency of batteries meant that other propulsion technology - such as electric trolleybuses or diesel buses - became commonplace.
The first battery buses were mostly small, mini- or midi- buses. The improvement of battery technology from around 2010 led to the emergence of the mass-produced battery bus, including heavier units such as 12.2-meter (40 ft) standard buses and articulated buses. China was the first country to introduce modern battery electric buses in large scale. In 2009 Shanghai catenary bus lines began switching to battery buses. In September 2010, Chinese automobile company BYD began manufacturing the BYD K9, one of the most popular electric buses
The first city to heavily invest in electric buses was Shenzhen, China. The city began rolling out electric buses made by BYD in 2011, with the objective of having a fully electric fleet. By 2017, Shenzhen's entire fleet of over 16,300 buses was replaced with electric buses, the largest fleet of electric buses of any city in the world.
According to Bloomberg, "China had about 99 percent of the 385,000 electric buses on the roads worldwide in 2017, accounting for 17 percent of the country’s entire fleet." Chinese cities are adding 1,900 electric buses per week.
Charging electric bus batteries is not as simple as refueling a diesel engine. Special attention, monitoring, and scheduling are required to make optimal use of the charging process, while also ensuring proper battery maintenance and safekeeping. Some operators manage these challenges by purchasing extra buses. This way the charging can take place only at night, which has the further advantage of mitigating the strain on the power grid since charging is then taking place while power consumption elsewhere is minimal. While this is a safe solution, it is also very costly and not scalable. Another solution is ensuring that the vehicle daily schedule takes into account also the need to charge, keeping the overall schedule as close to optimal as possible. Today, there are various software companies that help bus operators manage their electric bus charging schedule. These solutions ensure that buses continue to operate safely, without any unplanned stops and inconvenience to passengers.
Supercapacitors can be charged rapidly, reducing the time needed to prepare to resume operation.
The Society of Automotive Engineers has published Recommended Practice SAE J3105 to standardize physical automated connection interfaces for conductive charging systems since 2020. For communication between charger and electric bus the same ISO 15118 protocol is used as for passenger car charging. The only differences are in the charging power, voltage and physical interface.
Pantographs and underbody collectors can be integrated in bus stops to quicken electric bus recharge, making it possible to use a smaller battery on the bus, which reduces the initial investment and subsequent costs.
Battery electric buses offer the potential for zero-emissions, in addition to much quieter operation and better acceleration compared to traditional buses. They also eliminate infrastructure needed for a constant grid connection and allow routes to be modified without infrastructure changes, in contrast with a trolleybus. They typically recover braking energy to increase efficiency by a regenerative brake. With energy consumption of about 1.2 kW⋅h/km (4.3 MJ/km; 1.9 kW⋅h/mi), the cost of ownership is lower than diesel buses.
As of 2016 battery buses have less range, higher weight, higher procurement costs. The reduced infrastructure for overhead lines is offset by the costs of the infrastructure to recharge the batteries. In addition, the additional weight of batteries in a battery-electric bus means that they have a lower passenger capacity than trolleybuses in jurisdictions where there is a legal limit on axle loads on roads. Battery buses are used almost exclusively in urban areas rather than for long-haul transportation. Urban transit features relatively short intervals between charging opportunities. Sufficient recharging can take place within 4 to 5 minutes (250 to 450 kW [340 to 600 hp]) usually by induction or catenary. Finally, as with other electric-powered alternatives to fossil-fueled engines, battery electric buses are not a truly zero-emission solution if the power grid they rely on for charging is not also free of fossil fuel energy sources. The lithium batteries may also contribute to environmental pollution around the world where lithium mining takes place.
NREL publishes zero-emission bus evaluation results from various commercial operators. NREL published following total operating cost per mile: with County Connection, for June 2017 through May 2018, for an 8-vehicle diesel bus fleet, the total operating cost per mile was $0.84; for a 4-vehicle electric bus fleet, $1.11; with Long Beach Transit, for 2018, for a 10-vehicle electric bus fleet, $0.85; and with Foothill Transit, for 2018, for a 12-vehicle electric bus fleet, $0.84.
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