The World Health Organization (WHO) has identified the transport sector as a significant and growing contributor to the release of fine particles into the air. Land transport is responsible for 16.5% of total CO2 emissions, with an average annual increase of 3.3% between 2001 and 2015. Buses are in the crosshairs of this coordinated action, as travelers at bus stops are particularly exposed to gases and heat emissions. At the same time, land scarcity and urban population growth have become serious challenges for governments around the world. The urban population is expected to increase by an additional 2.5 billion people by 2050. (1)
Therefore, high investment funds are required for the expansion of the transport networks. Under budgetary pressure, this is the main factor behind the slowdown in the quality of public transport services. Under these demographic and socio-environmental pressures, global consensus on the urgency of the situation has resulted in remarkable advances in the efficiency of electric powertrains. It resulted in the further development of alternative fuel public transport buses such as fuel cell electric buses, battery-electric buses, and hybrid electric buses. In following, I would this column to lead readers towards finding the solution for the probable questions related to Electric Buses as a critical topic.
One of the few advantages fossil fuel vehicles hold over electric vehicles is the time it takes to charge or recharge. Remarkable efforts have been made to address pollution problems and fuel shortages. Transport agencies in different countries have provided different energy sources as alternatives to fossil fuels such as electric, hybrid, biodiesel and hydrogen technologies to create a greener environment. It should be noted that vehicles that run entirely or partially on electricity are on the rise and have great potential value. The change in major demand from global customers is the result of lower operating costs and emissions. The remaining electrification includes the costs of battery technology, battery life, number of charging stations and charging time overruns. (2)
ORLANDO’S E-BUS MAKES DEBUT. Image Credits: https://oucblog.com/orlandos-e-bus-makes-debut/
Alternative power plants for conventional internal combustion engines have varying degrees of electrification or hybrid power depending on the power plant architecture. They can be divided into three categories: battery electric buses (BEB), fuel cell electric buses (FCEB) and hybrid electric buses (HEB) or plug-in hybrid electric buses (PHEB). The main difference between the different technologies is the power supply of the electric motor. Except for hybrid parallel passenger cars (plug-in) that combine internal combustion and internal combustion engines, all types of alternative passenger cars are driven by electric motors. A reliable electric bus must have a certain number of functions according to (3):
It stores the energy required for maintenance operations;
Can operate safely;
Compact and light;
Can be charged frequently
At an affordable price, with a minimum Worn out batteries
Run at the fastest possible frequency.
Now, it is needed to be informed of the varied technologies that are used to provide different energy sources as alternatives to fossil fuels:
1. Battery electric buses (all-electric) are buses that run on energy stored in an on-board battery pack composed of multiple batteries, usually of the lithium-ion polymer type. The engine architecture does not contain any combustion process. For hybrid buses and fuel cell buses, it is very important for operation because it is the only energy source that powers the vehicle. The battery is also one of the heaviest components on the bus, so size is very important. In addition, energy storage technology is not yet fully mature, so the high-performance batteries required for pure electric buses are still the most expensive components. (4)
2. Hybrid electric buses are equipped with electric motors (EM) and internal combustion engines (ICE). ICE can run on diesel, gasoline, natural gas or biodiesel. Alternatively, the battery can be charged directly from an external power source. According to the configuration of EM and ICE, hybrid buses may have two main transmission system architectures (4):
The hybrid bus series use ICE to generate electricity to drive the electric motor. Due to excessive power generation, energy is transferred to charge the battery.
Parallel hybrid electric bus can drive electric motor and internal combustion engine at the same time. The connection between the internal combustion engine and the wheels is mainly used for road driving, while the EM is used for acceleration.
3. Fuel cell technology is based on the reaction between hydrogen and oxygen. During storage, the battery is filled with hydrogen. In contrast to internal combustion engines, combustion does not produce any driving energy, but the electrochemical reaction of hydrogen fuel with oxygen or other oxidant substances. The reaction between the components allows ions to migrate inside the electrolyte and to generate electrical energy to be delivered to the EM for movement, as long as the chemical actors are still available in the cell and are not fully consumed. It is also possible to couple this technology with an electric battery to gain more reach, analogous to hybrid powertrains. (4)
Gothenburg to have further 130 Volvo electric buses in operation. Image Credits:
In design section, most manufacturers have flexible designs that can adapt to customer needs and specific details of bidding. When comparing multiple sources of information and different locations, the specifications and prices of the manufactured electric buses will be different. The battery capacity, charging power and charging method depend on the combination of features selected for the bus model and the final target price category. In this part, product models are mainly used to promote production and improve marketing efficiency.
Also, the economic, ecological, operational and energetic aspects of the electrification of the public bus fleet were examined using models developed in different regions of the world. Most of this research follows a similar methodology based on three main phases: First, the bus routes and the specifics of the network are assessed. The energy demand is then taken into account, the consumption data is collected, the infrastructure and the charging strategy are modeled and the feasibility of the scenarios is analyzed. Finally, the restrictions in an electrical bus network are formulated mathematically and the optimized parameters such as the charging infrastructure, chargers, the rated power and electrification of the bus fleet are carried out.
In sum, it is essential to mention that concentrating on developing electric buses, as a critical player that has an important role in achieving the goals of sustainable development in the public transportation sector, should not be neglected in planning for the future. The electrification of conventional diesel-powered buses offers numerous advantages. It improves the efficiency of well to wheel (WTW), reduces energy consumption per vehicle kilometer and reduces local pollutant emissions. As a result, the switch to electric drives reduces foreign energy imports and increases the independence of gasoline prices. In addition, it enables better use of the roads and increases the comfort of travel perceived by passengers (e.g. noise, smells, vibrations). Finally, electric powertrains require less maintenance and ensure high reliability. Therefore, scientists and engineers in all fields are expected to take these aspects into account in their work in order to cultivate the industry of electric buses all around the world.
References:
(1) Song, Q.; Wang, Z.; Wu, Y.; Li, J.; Yu, D.; Duan, H., and Yuan, W. ‘Could Urban Electric Public Bus Really Reduce the GHG Emissions: A Case Study in Macau?’ In: Journal of Cleaner Production 172 (Nov. 2017), pp. 2133–2142. issn: 09596526.
(2) Mahdavian, A.; Shojaei, A.; McCormick, S.; Papandreou, T.; Eluru, N.; and Oloufa, A. ‘Drivers and Barriers to Implementation of Connected, Automated, Shared, and Electric Vehicles: An Agenda for Future Research’ In: IEEE, Feb.2021.
(3) Marcon. Electric Bus Feasibility Study - Edmonton Canada. June 2016.
(4) Williamson, S. S.; Wirasingha, S. G., and Emadi, A. ‘Comparative Investigation of Series and Parallel Hybrid Electric Drive Trains for Heavy-Duty Transit Bus Applications’. In: 2006 IEEE Vehicle Power and Propulsion Conference. 2006 IEEE Vehicle Power and Propulsion Conference. Windsor, UK: IEEE, Sept. 2006, pp. 1–10. isbn: 978-1-4244-0158-1 978-1-4244-0159-8.