The electric bus is one solution for cities to abandon fossil fuel dependency and may in a few years be the most cost-efficient renewable technique for public transport.
Options for Fossil-Free Transport
The transport sector is heavily dependent on fossil fuels. This has to change in order to meet global climate policy targets. In Sweden, the public transport authorities have a long history of testing different renewable technologies in their bus operations. Ethanol, biogas, and biodiesel are used extensively in all major cities. According to recent statistics, the share of renewable fuel in Swedish bus fleet traffic is 58 percent, and in some regions as high as 85 percent. These are impressive numbers and wonderful evidence that the technology is there and that a progressive policy really can make a difference.So what is the role of electric buses? Obvious advantages are lower noise levels and zero emissions which make it natural to regard electric buses as the next step for inner city bus fleets. Although biofuels are important elements of a sustainable transport system, the production potential is not sufficient to replace the huge quantities of oil now consumed. Electrification is necessary, and bus fleets are ideal to start with. A city with electric buses is truly “future ready” since the buses are climate neutral1 (provided that the electricity production is “green”), efficient and clean (see Figure 1).
Challenges with Electric Buses
The drivetrain of an electric bus is equipped with an electric motor. It is called a fully electric bus if the electric motor is the only motor that propels the bus and a hybrid electric bus if it is also equipped with a traditional combustion engine. The term plug-in is sometimes used and refers to the fact that it is charged from the grid. The electric motor can be fed with electricity in different ways, either from an on-board battery, from a direct supply like an overhead catenary for a tram, or from a fuel cell that creates electricity from hydrogen and air.Large-scale introduction of electric buses in a public transport system entails a number of important strategic and operative challenges. Conventional trolley buses, which draw electric power from overhead wires, are challenged by new concepts, such as battery buses with fast charging at the end stations. There are different solutions for battery charging and the driving-charging cycle. One strategy forward is to engage in several solutions, trying different charging techniques and types of batteries to see what works best under local conditions.
Charging Techniques
Different charging techniques are at different stages of technological maturity. Conductive charging, in which there is a direct physical contact that transfers the electricity at end stations, is currently the most wide-spread technology for which the costs are relatively easy to estimate (see Figure 2). Another example is inductive charging, which is a charging solution with little visual impact. Here electricity is transferred using electromagnetic fields instead of a physical contact. The equipment is mounted underneath the road surface and under the floor pan of the bus. It is sensible in environments where the presence of charging infrastructure is a sensitive issue. However, there are currently very few field trials with inductive charging from which to draw experience, and the costs are highly uncertain.An alternative strategy for battery charging and the driving-charging cycle is to let the market single out a cost-efficient and standardized solution before investing, to ensure long-term development of the chosen solution.
Cost Benefit Analysis of Electric Buses
As of now electric buses are, to varying degrees, more expensive than conventional buses. The purchase price is considerably higher than for conventional buses whereas the operating costs are lower due to lower energy consumption and easier maintenance. Therefore, electric buses should be used where their advantage is most accentuated. They should be used on routes that allow the buses to cover distances long enough to exploit their low operating costs. At the same time, the driving route should be structured in a way that limits the need for charging stations and the size of the battery pack.From an environmental perspective, calculations using conventional cost-benefit methodology show that electric buses should be used in densely built city environments, since that is where reductions of emissions of particles and nitrogen oxides benefits most people. The same applies to noise emissions: electric buses emit less noise than conventional buses, and the benefits will be greatest where most people dwell.
Electric buses and charging infrastructure are heavy investments which ideally should be amortized over their technical life span. When public transport is provided through procurement of public transport services however, the contract period may be too short for transport service companies (operators) to be motivated to make such investments, even when it would be the best choice for society at large.
To make use of the many benefits and promises of electric buses, city planning processes and business models for public transport must acknowledge the need to incorporate many essential stakeholders, for example city planning offices, public transport authorities, electricity providers, bus producers and charging equipment developers.
Figure 3 compares the cost per vehicle-kilometer for different types of buses, expressed in Swedish kronor. The term “Electric, mature market”, shown in Figure 3, refers to a situation in the near future in which the economy of scale has reduced the purchase price to a stable level.
The outcomes of comparative calculations, such as the one shown in Figure 3, are heavily dependent on assumptions about vehicle costs, amortization period, and yearly mileage. Therefore the cost comparison should only be seen as indicative. However, what should be clear is that, while electric buses may currently be on the verge of competing with other systems, a situation where vehicle and infrastructure costs are reduced by 25 percent (as shown by alternative “Electric, mature market”) would make electric buses highly competitive. This holds even when only monetary costs (fixed and variable) are considered.
The Role of WSP | Parsons Brinckerhoff
Electric buses are on trial or in implementation in half a dozen cities in Sweden, and the results so far are very promising. Some Swedish cities are now planning large scale implementation of electric buses, having the intention of replacing the entire city bus fleet. However, there are only a few places in the world where electric buses have been running in ordinary traffic for several years. Therefore, there is very little yet in terms of ex-post evaluations.WSP | Parsons Brinckerhoff in Sweden has worked with a few strategic studies for different clients, such as regional traffic administrations, a bus developer, and an electricity provider. For example, in the cities of Stockholm and Västerås, WSP | Parsons Brinckerhoff is engaged in strategic studies to see what the effects of large scale introduction could have on the environment and the economy. These are primarily ex-ante studies, trying to estimate effects on operating costs and environmental effects, such as reduction of carbon and noise emissions, and other metrics, based on the latest estimates from around Europe.
In 2015, WSP | Parsons Brinckerhoff conducted a strategic study on the electrification of the bus transit system in Stockholm, describing and discussing different bus types and charging techniques, experiences from other European cities, environmental effects, operative challenges, and important aspects for choosing a business model. The primary goal of the study was to investigate the potential for electric buses to help the Stockholm county reach its goals for energy efficiency in a cost-efficient way.
Currently, a similar study is being conducted for the nearby county of Vastmanland, but with a focus on the potential benefits of switching from biogas-fueled buses to electric ones. Since the county has invested in infrastructure for producing biogas, one important aspect of the study is to come up with alternative uses for biogas, and to clarify the need for sophisticated solutions for financing a new bus fleet, since the initial outlay is considerable and the benefits from lower distance-based costs can take many years to make the investment worthwhile.
Electrification of bus transit systems bring to the fore new stakeholders and important considerations about business models and compatibility of buses and charging infrastructure. WSP | Parsons Brinckerhoff has worked with electricity provider Vattenfall and the bus developer Volvo to suggest new solutions where, for example, the bus operator pays the electricity provider a set fee for charging that includes charging infrastructure and maintenance of that infrastructure. With such a solution, the balance sheet of the bus operator or the transport authority is affected less.
Conclusions
The concept of electric buses fits into city development strategies all over the world. All major cities struggle with poor air quality and noisy traffic. The electric bus is one solution for cities to abandon fossil fuel dependency and may in a few years be the most cost-efficient renewable technique for public transport.For successful implementation of electrified bus transport systems, careful analysis is needed to handle costs, infrastructure provision, and impact on the city environment. A global solution provider such as WSP | Parsons Brinckerhoff can help integrate electric bus schemes into new and existing city plans to ensure a “future ready” built environment with clean mobility. Imagine a complex of buildings in which electric bus stops are located indoors, serving people on their way to work or shopping. New perspectives open up when clean mobility and city development is designed in one process.
1 Climate neutrality is achieved by balancing the amount of emissions your day-to-day activities or business operations generate, with the same amount being reduced (offset) elsewhere in the world. Climate neutrality is not about zero emissions. It is about reducing current emissions to the point where we reach the ultimate balance between emissions and the absorptive capacity of the Earth. (Source: United Nations Framework Convention on Climate Change http://climateneutralnow.org/SitePages/FAQ.aspx)
