Electric bus
An electric bus is a bus that is propelled using electric motors, as opposed to a conventional internal combustion engine. Electric buses can store the needed electrical energy on board, or be fed mains electricity continuously from an external source such as overhead lines. The majority of buses using on-board energy storage are battery electric buses, where the electric motor obtains energy from an onboard battery pack, although examples of other storage modes do exist, such as the gyrobus that uses flywheel energy storage. When electricity is not stored on board, it is supplied by contact with outside power supplies, for example, via a current collector, or with a ground-level power supply, or through inductive charging.
As of 2017, 99% of all battery electric buses in the world have been deployed in Mainland China, with more than 421,000 buses on the road, which is 17% of China's total bus fleet. For comparison, the United States had 300, and Europe had 2,250. By 2021, China's share of electric buses remained at 98% while Europe had reached 8,500 electric buses, with the largest fleet in Europe being Moscow.
History
Principles
Battery
One of the most popular types of electric buses nowadays are battery electric buses. Battery electric buses have the electricity stored on board the vehicle in a battery. As of 2024, battery electric buses could have a range of over 350 km with just one charge, although extreme temperatures, hills, driving style and heavy loads can reduce range.City driving involves a great deal of accelerating and braking. Due to that, the battery electric bus is superior to diesel bus as it can recharge most of the kinetic energy back into batteries during braking, which reduces brake wear. The use of electric over diesel propulsion reduces noise and pollution in cities.
When operating within a city, it is important to minimize the unloaded and rolling weight of the bus. This can be accomplished by using aluminium as the main construction material. Composite paneling and other lightweight materials can also be used. According to Finnish bus manufacturer Linkker, its fully aluminium bus construction is about 3000 kg lighter than comparably sized modern steel buses, which have a curb weight of 9500 kg. Reducing weight allows for a greater payload and reduces wear to components such as brakes, tires, and joints, achieving cost savings for the operator.
Charging
Commonly, metropolitan electric busses are charged on-route with 6–8 minutes of charging at 450 kW for every hour of operation. Opportunity charging is available at bus stops with overhead chargers utilizing the SAE J3105 standard and at terminals at the end of the bus route. Slower, 50 kW to 175 kW overnight charging at plug-in chargers is utilized too. Sometimes wireless charging pads are utilized, but plug-in stations are more common due to the fact that are faster and more efficient.Wireless inductive charging with a charging pad under each bus stop and at each stop light was trialed in Korea with the Online electric vehicle project. Commercialization of the technology has not been successful, leading to controversy over the continued public funding of the technology in 2019.
Sweden conducted a program studying electric road systems technologies that allow buses and other vehicles to charge while driving on roads and highways. The four tested technologies were overhead wires, in-road rail and on-road rail known as ground-level power supply, and in-road inductive charging with coils. The final report published in December 2024 recommended against a national electric road network in Sweden as it would not be cost-effective, and the project was paused. From 2023 to 2027 France will conduct electric road studies with technologies by Alstom, Electreon, and Elonroad.
The first solar powered microgrid for charging electric buses in the US is under construction in Montgomery County, MD, and scheduled for completion in fall of 2022.
Capacitors
Buses can use capacitors instead of batteries to store their energy.Ultracapacitors can only store about 5 percent of the energy that lithium-ion batteries hold for the same weight, limiting them to a short distance per charge.
However, ultracapacitors can charge and discharge much more rapidly than conventional batteries.
In vehicles that have to stop frequently and predictably as part of normal operation, energy storage based exclusively on ultracapacitors can be a solution.
China is experimenting with a new form of electric bus, known as a capabus, which runs without continuous overhead lines by using power stored in large on-board electric double-layer capacitors, which are quickly recharged whenever the vehicle stops at any bus stop, and fully charged in the terminus.
A few prototypes were being tested in Shanghai in early 2005. In 2006, two commercial bus routes began to use electric double-layer capacitor buses; one of them is route 11 in Shanghai. In 2009, Sinautec Automobile Technologies, based in Arlington, VA, and its Chinese partner, Shanghai Aowei Technology Development Company are testing with 17 forty-one seat Ultracap Buses serving the Greater Shanghai area since 2006 without any major technical problems. Another 60 buses will be delivered early next year with ultracapacitors that supply 10 watt-hours per kilogram.
The buses have very predictable routes and need to stop regularly, every, allowing opportunities for quick recharging.
The trick is to turn some bus stops along the route into charging stations. At these stations, a collector on the top of the bus rises and touches an overhead charging line. Within a couple of minutes, the ultracapacitor banks stored under the bus seats are fully charged. The buses can also capture energy from braking, and the company says that recharging stations can be equipped with solar panels. A third generation of the product, will give of range per charge or better.
Such a bus was delivered by Chariot Motors in Sofia, Bulgaria in May 2014 for 9 months' test. It covers 23 km in 2 charges.
Sinautec estimates that one of its buses has one-tenth the energy cost of a diesel bus and can achieve lifetime fuel savings of $200,000. Also, the buses use 40 percent less electricity compared to an electric trolley bus, mainly because they are lighter and have the regenerative braking benefits. The ultracapacitors are made of activated carbon, and have an energy density of six watt-hours per kilogram, but the ultracapacitor bus is also cheaper than lithium-ion battery buses, about 40 percent less expensive, with a far superior reliability rating.
There is also a plug-in hybrid version, which also uses ultracapacitors.
Sinautec is in discussions with MIT's Schindall about developing ultracapacitors of higher energy density using vertically aligned carbon nanotube structures that give the devices more surface area for holding a charge. So far, they are able to get twice the energy density of an existing ultracapacitor, but they are trying to get about five times. This would create an ultracapacitor with one-quarter of the energy density of a lithium-ion battery.
Drawbacks
As with other electric vehicles, climate control and extremely cold weather will weaken the performance of electric buses. In addition, terrain may pose a challenge to the adoption of electric vehicles that carry stored energy compared to trolleybuses, which draw power from overhead lines. Also, compared to trolleybuses, battery electric buses have lower passenger capacity because the weight of the batteries increases axle loads in jurisdictions where there are legal axle load limits on roads. Even when conditions are favorable, internal combustion engine buses are frequently diesel powered, and diesel is relatively inexpensive per mile. High local utility rates and proprietary charging systems pose barriers to adoption.In Motion Charging
Battery electric trolleybuses with In Motion Charging technology electric buses that can charge dynamically via an overhead contact network and can run on batteries for up to half of their route. The on-board battery is charged while the vehicle is in motion under the overhead wires and then allows off-wire travel for significant distances, often between.Makers and models
School use
North America
In 2014, the first production-model all-electric school bus was delivered to the Kings Canyon Unified School District in California's San Joaquin Valley. The Class-A school bus was built by Trans Tech Bus, using an electric powertrain control system developed by Motiv Power Systems, of Foster City, California. The bus was one of four the district ordered. The first round of SST-e buses is partly funded by the AB 118 Air Quality Improvement Program administered by the California Air Resources Board.The Trans Tech/Motiv vehicle has passed all KCUSD and California Highway Patrol inspections and certifications. Although some diesel hybrids are in use, this is the first modern electric school bus approved for student transportation by any state.
Since 2015, the Canadian manufacturer Lion Bus offers a full size school bus, eLion, with a body made out of composites. It is a regular production version that is built and shipped in volume since early 2016, with around 50 units sold until 2017.
In February 2021, there were about 300 electric school buses in operation in the United States. That month, Montgomery County, Maryland approved a contract to transition its 1,400 vehicle school bus fleet to electric buses by 2035, with the first 25 buses arriving in fall 2021.
The 2021 Infrastructure Investment and Jobs Act included $2.5 billion in funding for electric school buses, to be distributed over five years.
By June 2022, 38 US states were using electric school buses. As of July 2023, 909 school districts and private fleet operators across all 50 states plus five tribal nations and territories had received funding for, ordered, taken delivery of, or were already operating electric school buses.
In September 2022, EPA funding for electric school buses was doubled, from $500 million to almost $1 billion, due to high demand. The improvement in air quality over diesel powered school buses is expected to be helpful for children with asthma. In addition, the BIDIRECTIONAL Act was introduced in the US Senate, to "create a program dedicated to deploying electric school buses with bidirectional vehicle-to-grid flow capability."