Reducing emissions is a major challenge for the 21st century. The negative effects of ever increasing emissions are felt at global and local level. There is no doubt that reducing the use of fossil fuels can help to tackle the problem, and the transport sector can contribute to this by using conventional fuels more efficiently and by promoting the use of vehicles powered by electricity from renewable energy sources.
The constant changes in transport modes and means of transport affect all our lives. Technological progress means that we get from one place to another in different ways from time to time. We are already seeing the emergence of electromobility, and it is inevitable that the results of research into artificial intelligence and self-driving will be reflected in vehicles. The explosion in the number of electric vehicles seems unstoppable, but there is no getting around the sustainability issues of production and operation. While total vehicle sales in 2020 were down by a third, sales of electric vehicles were around double those of the previous year. The European Parliament recently voted that from 2035, new cars produced in Europe should be electric only.
Today, the dynamic electrification of public transport is also unstoppable. A visible manifestation of this is the implementation of ambitious programmes for the deployment of electric bus fleets in Europe, North America and India. But these regions can only follow China, where the number of electric buses is significantly higher than anywhere else in the world: there are now some 421,000 battery-powered buses on the streets of Chinese cities.
The electrification of bus fleets has a significant impact on operators' operating costs and cost structures. Vehicle procurement, energy consumption, infrastructure, maintenance and operating costs are all significantly different from those of diesel buses.
In recent decades, the main indicator for the purchase of diesel buses has been to keep the average vehicle life below a certain level. Capacity, comfort and engine performance have been the most important considerations for purchases. Because of the high energy density of gas oil, range was not an important factor. For electric buses, the situation is quite different: the range on a single charge is mainly determined by the capacity of the batteries. Larger/more batteries increase the range, but also the weight of the vehicle, which has a negative impact on fuel consumption and therefore on range, thus increasing the unit running costs. Although a number of promising energy storage technologies are under development, the use of limited capacity lithium-ion batteries will remain predominant in the foreseeable future.
Of course, the aim remains to minimise fleet size and operating costs. As the mileage per vehicle in public transport is high, the higher investment costs of electric buses may be compensated by lower maintenance costs. Therefore, transport companies are also exploring and implementing new models for financing, in addition to minimising their costs through more efficient use of assets.
The main difficulties arise from the limited range and charging time requirements. The daily mileage "expected" from a bus is usually greater than the range that today's batteries allow. In total, a bus on urban lines can run up to 16 hours a day. Thus, intra-day recharging needs to be scheduled. Cost-effective planning, both in terms of scheduling and outages, and in terms of the number and composition of vehicles and the optimum amount of infrastructure required, is therefore of paramount importance.
In order to put together the optimal and most efficient mix for a given context, it is essential that fleet management software takes into account the new factors associated with electromobility, using different models to meet the challenges of the times, and is able to provide a much more complex turnaround planning. The optimisation already used for conventional vehicles needs to take into account the range of the vehicles under different conditions, the scheduling of charging times and the allocation of charging infrastructure between vehicles, and even the optimal charging practice in terms of battery wear.
The cost structure is essentially a function of the type and proportion of buses and coaches placed on the market. The energy consumption of a short-range, lighter vehicle can be up to one third lower than a long-range vehicle, but the overheads (km, vehicle and human resources) are higher than for a site charging. Experience shows that a mixed fleet adapted to the characteristics of the routes can be the most efficient.
The difference between electric buses and coaches is mainly due to the charging technologies used.
In terms of infrastructure, there are basically two types of solution:
- on-site charging of longer range buses, with service interruption by means of a cable
- frequent rapid charging of shorter-range buses during the service (interchange)
The advantage of on-site charging is that no special charging points are needed and the charging station locations are given. The majority of operators prefer on-site charging mainly because the entire charging infrastructure can be on their premises. In addition, two of Europe's major bus manufacturers, Daimler and MAN, have announced that they are focusing their product portfolios on buses with larger battery capacities. The drawbacks of this technology are the already mentioned negatives of a heavy battery, long charging times and the concentrated charging power required. The latter can be addressed by rapid, robotised replacement of discharged batteries with charged modules, tested in Shanghai: a complete replacement takes about 12 minutes from arrival to departure.
The advantage of on-the-fly charging is that the lighter battery packs result in lower energy consumption and overall reduction in site overheads, with even minimal changes to schedules compared to conventional operation. Another advantage is that charging power can be decentralised. The disadvantage, however, is that these charging facilities are currently more costly and that cooperation with local authorities is more important in determining the location.
In both cases, charging can be by wire or induction.
A promising solution for wireless charging is the North American Momentum Dynamics system, which uses induction chargers built into the road surface to keep bus batteries at the right charge level for up to a full shift.
The OppCharge wired charging systems from ABB TOSA and VOLVO Bus in Switzerland (using a pantograph solution similar to the current collector of a tram) can also reduce or even eliminate unnecessary power consumption. Of course, special (lithium-titanium) batteries are also required for fast, short (3 minutes on average) charges.
Whichever solution is used, the new approach to public transport charging systems will in any case be more closely linked to smart energy networks, taking advantage of the mobile energy storage potential of buses and the technical possibility of on/off charging. The new system is called V2G (vehicle two grid). This will allow both balancing of the electricity grid and time-shifted use of renewable generation!
What about micromobility? Let's not forget that it is part of public transport and as such is an element of the charging network: it involves the use of small, lightweight, electric motor-driven (possibly human-powered or a combination of both), limited speed vehicles (micro-vehicles), and the use of these - a complete nova in transport terms. Its spread is facilitated by urbanisation processes, the protection of our environment, the rise of more efficient batteries, smart devices, the development of GPS systems and increasingly sophisticated route planning solutions!
Finally, however, we must point out that there are currently difficulties in gaining acceptance for charging stations that affect the urban landscape, with the public and NGOs, and that this issue must also be addressed, and cannot be seen as a purely functional challenge.