An electric bus is a bus that is powered by electricity.
Electric buses can store the electricity on board, or can be fed continuously from an external source. Buses storing electricity are majorly battery electric buses, in which the electric motor obtains energy from an on-board battery, although examples of other storage modes do exist, such as the gyrobus which uses flywheel energy storage. In the second case, electricity is supplied by contact with outside power sources. For example, overhead wires, as in the trolleybus, or with non-contact conductors on the ground, as seen in the Online Electric Vehicle. This article mostly deals with buses storing the electricity on board.
As of 2017, 99% of electric buses have been deployed in China, with more than 385,000 buses on the road, which is 17% of China’s total bus fleet.
Electric vehicles have been around since the 19th century. In the early 19th century, researchers in Hungary, the Netherlands, and the United States began exploring the idea of battery-powered vehicles. There had previously been progress with an electric carriage, a horseless carriage that was powered by an electric motor. However, as people wanted to get around more easily and quickly, cars became a faster and more reasonable alternative to horse-drawn carriages.
In 1835, American Thomas Davenport is credited with building the first practical electric vehicle, a small locomotive. He developed a battery-powered electric motor which he used to operate a small model car on a short section of track.
The first successful electric car was made in the United States in 1890. William Morrison of Des Moines, Iowa, built an electric vehicle that could hold up to six passengers and could reach from 6 to 12 miles per hour. Specifications for the 1890 Morrison Electric included 24 storage battery cells mounted under the front seat. The vehicle could travel for a range of 100 miles before needing to be recharged.
This initial invention helped spark interest in electric cars, and automakers started building their own versions around the globe. Due to the extreme sudden interest, electric cars reached their peak popularity by 1900 and made up a majority of all vehicles on the road.
At this time electric cars were the preferred vehicles. Gasoline-powered vehicles required a lot of effort to drive, from changing gears to starting the engine with a hand crank, as well as other cons like strong and unpleasant exhaust fumes.
However, improvements were made to the gasoline-powered car that caused the electric car to lose some momentum. The hand crank was soon replaced with an electric starter and gasoline-powered vehicles became more affordable. Gasoline cars soon overcame the popularity of electric powered vehicles.
By 1935, electric cars practically disappeared. It was not until the 1970s when a gas shortage hit, causing gas prices to soar, that electric cars entered back into the marketplace. Gasoline-powered cars still remained more popular due to better performance and reliability.
The 1990s saw electric cars made more popular as societal concern for the environment began to rise. At the start of the 21st century, the technology of electric cars looked more promising than ever with the release of the Toyota Prius, the first majorly manufactured electric vehicle. Today, electric vehicles are on the rise and continue to advance as more Americans demand a more efficient and eco-friendly vehicle.
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. Even when conditions are favorable, high local utility rates (especially during periods of peak demand) and proprietary charging systems pose barriers to adoption.
Battery electric bus
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. Today such buses can have a range of over 200 km with just one charge. These buses are usually used as city buses due to particularities in limited range.
City driving is majorly accelerating and braking. Due to this, the battery electric bus is superior to diesel bus as it can recharge most of the kinetic energy back into batteries in braking situations. This reduces brake wear on the buses and the use of electric over diesel can improve air quality 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 for a bus. Composite paneling and other lightweight materials can also be used. According to Linkkebus their fully aluminium bus construction is about 3000 kg lighter than comparably-sized modern steel buses (curb weight 9500 kg). Reducing weight allows for a greater payload and reduces wear to components such as brakes, tires, and joints bringing cost savings to the operator annually.
Proterra’s EcoRide BE35 transit bus, called the Ecoliner by Foothill Transit based in West Covina, California, is the world’s first heavy duty, fast charge, battery-electric bus. Proterra’s ProDrive drive-system uses a UQM motor and regenerative braking that captures 90% of the available energy and returns it to the TerraVolt energy storage system, which in turn increases the total distance the bus can drive by 31-35%. It can travel 30–40 miles on a single charge, is up to 600% more fuel-efficient than a typical diesel or CNG bus, and produces 44% less carbon than CNG.
Charging electric bus batteries is not as simple as refueling 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. It is a safe solution, but also very costly and not scalable. The real 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.
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 coupler.
Pantographs and underbody collectors at bus stops
Pantographs and underbody collectors are 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.
Autonomous (self-driving) electric buses
An autonomous bus is an electrically-powered, self-driving vehicle that transports twelve or more passengers. Autonomous buses are operated without a driver inside the vehicle, instead utilizing cameras, sensors and remote controls to properly steer their way through traffic.
There is a 40-foot (12.2 m) pure electric bus being developed, using a pre-commercial battery technology. Electric Fuel Corporation is developing and demonstrating a 40-foot (12.2 m) electric bus powered by a zinc air cell, along with an ultracapacitor. The zinc-air energy device, often described as a battery, converts zinc to zinc oxide in a process that provides energy to the bus. The bus is not recharged; instead, the zinc oxide cartridges are swapped out for new zinc ones. This bus has shown a range of over 100 miles (160 km) in testing and has been demonstrated in Las Vegas, Nevada. However, this technology is in the development phase, and several major hurdles must be overcome before it can be adopted for transit fleet use, including available refueling infrastructure or use in bus stations.
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 couple of miles 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 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 (under so-called electric umbrellas), 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 3 miles (4.8 km), 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 a few feet 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 20 miles (32 km) of range per charge or better. Such a bus was delivered 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 (for comparison, a high-performance lithium-ion battery can achieve 200 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 ultracaps.
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.
Future developments includes the use of inductive charging under the street, to avoid overhead wiring. A pad under each bus stop and at each stop light along the way would be used.
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 (as they are called) 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 the late 1990s, electrical technology was gradually incorporated into autonomous vehicles. Vehicles cleaner than conventional diesel buses and more independent than trolleybuses have been developed: this is the appearance of hybrid buses. These vehicles combine two engines, an electric and a thermal, to allow a more optimal use of the fuel (savings of 10 to 30%). However, although they use the technology of electric traction and kinetic energy recovery (or even for some storage of energy in batteries then called rechargeable hybrid vehicle)), they operate thanks to the fuel unlike the electric bus whose source of energy is only electricity.
Autonomous electric buses
Today, autonomous electric buses are in development and some manufacturers (Power Vehicle Innovation, Renault Trucks,…) are able to offer sufficient autonomy to allow operators to provide an urban transport service without constraints. infrastructure. Some have been in use for several years, such as Montmartrobus, a bus operated by the Régie Autonome des Transports Parisiens (RATP) since 2000. Buses powered by supercapacitors (Tosa line of Geneva) would represent an investment cost less than that of a line oftrolleybus, on the order of one million euros per Km.
The electric buses operate on the same principle as the thermal buses, that is to say thanks to a traction chain operating with an electric motor that is powered by batteries (the energy storage is adapted to electricity by the use of accumulator batteries instead of the fuel tank of the thermal vehicles). The power obtained with electric motors allow sufficient speeds for urban use (more than 70 km / h).
From the point of view of energy storage, it is essentially battery technology that has evolved in research (especially lithium-ion batteries with higher specific gravity). Today, this technology allows for the sustainable use of contemporary models and the development of the electric bus in addition to the awareness of the environmental impact of conventional transit vehicles. Although they occupy more space than a fuel tank, batteries can today, occupying a place reasonable enough that we do not notice, This autonomy is especially improved through the kinetic energy recovery system during deceleration or braking phases, recovering up to a threshold of 20%. Compared to Diesel technology, the energy efficiency of electric vehicles is approximately 90% overall, compared with 40% for gasoline vehicles.
In use, an electric bus emits no greenhouse gases. The electricity generation can it, according to its manufacturing process, result in greenhouse gas emissions (such as carbon dioxide): the carbon footprint of an electric bus is not zero but tends towards very low levels of pollution.
An electric bus makes very little noise compared to the heat bus and could therefore if it were generalized to improve the quality of life of urban environments by reducing the noise pollution of public transport vehicles.
Adaptation to the urban landscape
The combined ecological and environmental benefits allow electric buses to be unobtrusive and clean (the absence of greenhouse gas emissions is not a problem as would a heat bus in areas heavily frequented by pedestrians). These characteristics have often been retained for use in the city: many small electric buses to be used in the city center in residential areas and narrow streets frequented by pedestrians.
Electric energy is cheaper to use than fuel, charging a small electric bus is 2 euros. However the cost of electric buses varies greatly depending on the type of bus: Trolleybus, bus with capacitors, Gyrobus, Hybrids.. Some studies, however, estimate the cost of a battery electric bus as representing an investment cost and operating 5 to 10 12 times higher than a trolleybus.
Autonomy is not yet as important as that of thermal vehicles. However, while the lower autonomy of batteries for electric vehicles seems a technological limit to the use of electric vehicles for individual use 13, the application of electric vehicles for bus journeys is more rational. Advance path length, starting point, end point and installation calculations can easily be made accordingly. In addition, the research carried out in this field continues, firstly to improve the battery life, and secondly to make recharging batteries faster thanks to supercapacitors.
Charging points for electric vehicles are currently not as widespread as petrol stations, but these infrastructures tend to be less and less heavy
Electric buses represent an investment to purchase (more expensive than a thermal bus type Diesel) although the savings in terms of energy consumption can follow: the price of electricity being overall lower that of fuel (because of the TIPP) and the best energy efficiency. Thus, for comparison, of the cost of operating trolleybuses, is lower than that of a tram, which cost himself at least less than half of to that of a diesel bus.
Source from Wikipedia