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What Is an E-Bus?

What is an e-bus?
Electir Bus in the streets of Nairobi, Kenya.

In our rapidly evolving world, the need for sustainable and eco-friendly transportation solutions is more critical than ever. As urbanization continues to grow, traffic congestion and environmental concerns are escalating. E-Buses are a promising innovation in public transportation.

This article is intended to:

  • explain, what an E-Bus is
  • show the structure and different types of E-Buses
  • provide examples of successfully implemented E-Bus fleets.

What is an E-Bus?

Definition:

An E-Bus is propelled using electric motors instead of an internal combustion engine. E-Buses can store the needed electricity on board or be fed continuously from an external source.

Autonomy & range:

Their autonomy or range depends on the battery size and the duty cycle (operational parameters; for example, topography, climate, weight, determine battery life).

Charging:

Battery buses are charged statically using mechanical and electrical equipment. The most common charging technologies are conductive charging via plug-in charger and pantographs.

Structure & Function

  • There is no engine or fuel tank in an E-Bus. Instead, the electric motor on the bus serves as the engine and transmission, while the battery is essentially the ‘fuel tank’.
  • E-Buses send a signal to the powertrain system controller. That signal powers up the high-voltage battery, where chemical energy is stored and converted into electrical energy.

Image of an electric bus from the inside, showing its internal components. Components inside an E-Bus. Electric Motor Engineering (2022)

Course Mascot with the text "We will go more into detail about this topic in further steps!" Course Mascot. PEM Motion (2023)

Different Types of E-Buses

Hybrid Electric Bus (HEB):

A hybrid bus combines two power sources in the vehicle drive train such as a conventional diesel engine and an electric motor. The hybrid system enables energy to be recovered during braking and then released to accelerate the vehicle, as shown in the next diagram.

Diagram explaining the process of energy generation for a Hybrid Electric BusClick to expand. Components inside an Hybrid Electric Bus. PEM Motion (2023)

Fuel Cell Electric Bus (FCEB):

A fuel cell electric bus is an all-electric zero-emission solution that operates similarly to a diesel bus and hence is marketed as the closest option to replace conventional diesel buses. The energy generation for this type of bus is shown in the next diagram:

Diagram explaining the process of energy generation for a Fuell Cell Electric Bus Click to expand. Components inside a Fuel Cell Electric Bus. PEM Motion (2023)

Battery Electric Bus (BEB):

A battery electric bus is driven by an electric motor and obtains energy from on-board batteries, as shown in the next diagram:

Diagram explaining the process of energy generation for a Battery Electric BusClick to expand. Components inside a Battery Electric Bus. PEM Motion (2023)

Trolleybus:

A trolleybus is an E-Bus that draws power from dual overhead wires (generally suspended from roadside posts) using spring-loaded trolley poles, as shown next:

Diagram explaining how a trolleybus obtains energy.Click to expand. Components inside a trolleybus. PEM Motion (2023)

Charging Solutions and Strategies

Several charging solutions and different technologies are already available on the market for E-Buses.

These technologies are selected based on operational needs and the surrounding environment. For example, the bus can be recharged along the route, or be charged overnight at a depot. These charging strategies may be selected depending on factors such as the duration of daily operation, and its battery capacity.

A diagram showing the different parts that are involved when a E-Bus is charging, including the charger converter, the contact and a pole-mounted connector.Click to expand. Parts involved in the charging process. Diez & Restrepo (2021)

Overnight Charging:

  • takes places during non-service hours at the depot, such as overnight, hence the name ‘overnight charging’
  • also called slow charging or low-powercharging, this method typically takes 4–6 hr (DC plug charging at 50 kW or above)
  • charging infrastructure is located only at the depot premises.

Opportunity Charging:

  • takes place during operation, either along the route, terminals or bus depot (depending on its location) or charging hubs. Also called fast charging, high power DC 150kW or above.
  • charging infrastructure can be located along route and at the depot, and different technologies applicable according to location and strategy (conductive/inductive charging).

Pantograph Charging:

Pantograph type charging can be used to charge E-Buses on routes and at the depot.

There are two different types of pantograph charging (roof-mounted and inverted). Depending on the type of pantograph charging, the pantograph will extend itself, connect the bus to the charging station, and charge the batteries.

During opportunity charging, the E-Bus will stop at bus stops and use the time of on-boarding and off-boarding passengers to charge its batteries.

For overnight charging, the bus will use the pantograph to charge its batteries overnight at the depot.

The main advantage of this type of charging method is that the pantograph charger has a high charging power and can therefore charge E-Buses within a short time.

Icon of a drawing representing pantograph charging. Icon of pantograph charging. BSD in Flaticon (2023)

There are two main types of pantographs, which are explained in the next diagrams:

Diagram with text boxes explaining the roof mounted pantographs and the inverted pantographs plus their characteristics and a drawing as an example of each one.Click to expand. Types of pantograph charging. PEM Motion (2023)

Plug-in Charging

The process of charging involves a physical connection between the bus and the charger using a cable:

  • a plug-in connector is primarily used for overnight charging
  • the charging method involves physically plugging in a cable from the charging station to the E-Bus
  • the advantages of this charging method are that it is quite simple and can be easily installed at depots, and no special infrastructure is needed throughout the city.

Icon with a drawing of a bus with a charging plug. Icon representing an E-Bus charging. Flaticon (2023)

Plug-in Charging Types:

Interoperability between different vehicle and infrastructure manufacturers is made possible using standardized plugs, but for complete compatibility, it’s essential to standardize both the plug and the communication protocol:

  • there are different types of charging plugs which are similar to those used for other EVs
  • plug-in charging types can vary depending on different manufactures of vehicles, and a nation’s infrastructure
  • the examples present show a Type 2 (AC connection) plug, and a Combo Type 2 (DC connection), this plug is also known as CCS plug (Combined Charging System).

Picture of a type 2 AC Charging Plug. Type 2 plug (AC-charging). Rogge (2020)

Picture of a Combo Type 2, DC Charging Plug. Combo Type 2 (DC-charging). Rogge (2020)

Ground-Based Charging

With this technology, cities can run electric fleets that are clean and quiet, without the need for unsightly or obstructive masts or overhead lines. This presents a significant advantage for cities that face architectural or spatial constraints, such as narrow streets or bridges, where traditional overhead infrastructure is not feasible or practical.

  • Ground-based charging is a new innovative method to charge E-Buses.
  • Ground-based charging is used to charge E-Buses along routes.
  • The charging strategy works by having rails or pads embedded on the surface of the road at bus stops.
  • When the E-Bus is stationary during bus stops, a device drops down from under the bus and contacts the charging pad to charge the battery.
  • The advantages of this charging strategy are that this is a quick way to recharge E-Buses, and not much space is taken up by implementing charging infrastructure

Icon with a drawing representing ground-based charging for e-buses. Icon representing ground-based charging. Flaticon (2023)

Across the globe, cities are electrifying their public transportation networks, leading to the successful implementation of E-Bus fleets. These initiatives represent a transformative shift toward cleaner and more sustainable urban transit options. In this overview, we highlight some notable examples of E-Bus fleets in action from various cities around the world.

Overview with different pictures of e-buses implemented in countries all over the world and their quantity.Click to expand. Global examples of E-Bus implementation. PEM Motion (2023)

Conclusion

In conclusion, the electrification of bus fleets is not just a vision for the future, but a reality shaping the present. As we’ve explored the diverse array of E-Bus technologies, charging solutions, and real-world implementations, it becomes evident that cities worldwide are driving the transition toward sustainable urban transportation.

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