Objective of Task

The objective of Task 33 was to analyse and assess the current state of technology and demonstration experiences of battery electric buses towards a broad market roll out. This covered on one hand the bus technology, e.g. battery or capacitor system, and on the other hand charging infrastructure, e.g. fast charging stations at the bus stop and its optimal integration in an urban infrastructure, e.g. synergies with trams, metro or trolley bus systems.

The task analysed ongoing demonstration projects and the start of the roll out phase of battery electric buses worldwide. Based on this, the future perspectives and challenges for battery electric buses were to be analysed and described. This included the identification of major challenges e.g. technology, costs, public acceptance and the necessary R&D demand.

The work was undertaken in close collaboration with relevant stakeholders from the three groups:

1. Providers of public transportation services.
2. System and technology providers.
3. Research institutions.

The outputs were documented and disseminated via presentations, workshops, conference contributions and publications.

The major activities:

• Identification and analysis of technology and systems of battery electric buses.
• Collection and documentation of “International Success Stories” .
• Overview of systems and technology providers with characteristic data.
• Stakeholder workshops, in combination with site visits.
• Analysis of the combination of trolley and battery bus systems.
• Analysis of the integration and use of existing infrastructure of trams, trolleys and metro.
• Identification of success factors, e.g. size of bus, distances between bus stops,
• Describing and defininig various loading strategies.
• Analysis of sustainability issues – economic, environmental and social aspects,
• Identification of  R&D demand.
• Conclude and summarise future perspectives.
• Presentations and contributions at conferences.

Working Method

The most important activity of the working method (Figure 1) was the organisation of workshops in different member countries to involve the stakeholders in the value chain of battery electric buses, e.g. providers of public transportation services, system and technology providers, research institutions.

The organisation of workshops with participation from industry, research organisations, technology policy experts and governmental institutions provides an international basis for the exchange of information on the relevant activities. The focus of the expert workshops was to analyse, discuss and document two areas:

1. The state of technology for battery electric buses.
2. Future perspectives of battery electric buses.

The workshops were combined with site visits to demonstrate on-going activities of battery electric buses in daily life application.

Figure 1 Working Method

Results

The results of this task pertained to the key reasons for adoption for battery electric buses including the technological aspects, Experiences from demonstration projects and experiences, Fleet management, Performance indicators, Environmental aspects, Economic aspects, and the Comparison to other low-or zero-emission bus systems.

The charging systems are an essential component, when discussing battery electric bus implementation. Harmonised charging systems are necessary for fast and/or opportunity charging on the route or in the depot. Currently there is no “one size fits all” charging solution as the site specific framework conditions have to be considered. For effective grid load management, a charging management of the bus fleet is essential; furthermore, a system approach combining bus operation and charging strategies is necessary – bus and charging infrastructure must be optimally linked.

One very important aspect for the further future development of battery bus systems is advanced fleet management. Fleet management can be utilised to optimise the operation of electric bus systems. Especially when high scale OC bus systems are considered, fleet management has functions to ensure optimal charging operations.

The key performance indicators for battery electric bus systems are:

• Operating costs and energy consumption.
• Charging system performance.
• System performance.

As additional indicators the following are relevant:

• Powertrain electricity consumption (kWh/km): inverter consumed electricity / kilometres driven (on route)
• Heating electricity consumption (kWh/km): electricity consumed by the HVAC system (both on route and total)
• Auxiliaries electricity consumption (kWh/km): electricity consumed by other electric auxiliaries, such as power steering, air compressor and DC/DC (on route)
• Fuel consumption (l/h): fuel heater fuel consumption vs. temperature
• Charging efficiency (%): electricity from the grid / Electricity into the battery
• Dead time in charging (%): Dead time in charging / total charging time
• Battery efficiency (%): electricity out from the battery / Electricity into the battery
• Total system energy efficiency (%): electricity out from the battery / Electricity from the grid
• Minimum SoC in operation: lowest battery state of charge in operation
• Average delta SoC in operation: estimate from operational data
• Battery health, SOH (%): Percentage of the remaining battery capacity versus battery nominal capacity

Besides battery electric buses, hydrogen fuel cell buses, and synthetic biofuels and E-fuels (made from CO2 and electricity) with an internal combustion engine (ICE) are also future options for low- or zero-emissions bus systems. The application of biomethane and hydrotreated vegetable oil (HVO) is an option; in future the application of synthetic biofuels is also possible.

Focusing on current trends it can be observed that the battery capacity of both OC and DC buses is continuously increasing. Different sizes of battery electric buses are available, ranging from 12, 15 and 18 m buses. For the design of new light weight battery electric buses, more aluminium and plastic components are set to be developed and integrated in innovative new use concepts.

Mass roll out of battery electric buses does however come with some main challenges:

• Availability of battery electric buses and charges in daily operation (as less/ no diesel buses are there for backup).
• Integration of fleet management.
• Energy and charging management to reduce cost and power capacity, and
• Grid stability and quality.

Focusing on the further development of battery electric buses, R&D needs are identified in the following fields:

• heating and cooling systems and strategieS.
• Inductive charging at stations/road.
• High power charging 1 MW and higher.
• Light weight vehicles, e.g. plastic and aluminium.
• Additional capacities to batteries for very quick charging.
• Bus to grid (B2G) concepts, applications and business models.
• Integration of 2nd life batteries in depot charging system for peak shaving and additional renewable electricity storage.