Electric buses are regarded as more comfortable than their traditional counterpart and produce no local emissions. However, the limited battery and the lack of a network of battery charging facilities have limited their expansion. Inductive charging systems tackle these problems by providing wireless charging points along bus routes. Torino has been using this technology on two of its bus lines for over 10 years.
Context
To improve air quality in the historical city centre, Torino decided to convert it into a Limited Traffic Zone (LTZ), allowing access to a limited number of authorised vehicles. Other drivers must park in one of the Park-and-ride (P&R) facilities along the rim of the LTZ, so to get the drivers to the centre, Torino launched in 2003 the STAR 1 line. A few months later, on citizens’ request, the service was expanded. The line serves important points in the city centre (two hospitals, university departments, the courthouse and tourist attractions). Its success led Torino’s public transport operator, GTT, to launch STAR 2 in September 2007 to cover important areas of the historical city centre, the Porta Susa railway station and to connect with other public transport lines and the metro. Both lines – each around 13km long - use the inductive charging system.
In action
The inductive charging system is based on the IPT® (Inductive Power Transfer) magnetic resonance coupling technology, which provides an efficient, automatic and contactless energy transfer. The system consists of primary coils connected to the electrical grid, and a secondary coil integrated in the floor of each of the electric buses. The battery is fully charged overnight and topped up during the day (by about 10-15 per cent) along the bus route – for example, at terminals and railway stations - with short and relatively frequent charging sessions. In normal operating conditions, 95 per cent of the energy taken from the electricity grid is stored in the bus battery. The frequent top-ups mean that the capacity of the buses’ batteries can be kept at a minimum (reduced by as much as 75 per cent) potentially saving money through the purchase of smaller batteries and making the vehicle lighter.
Two charging points were installed at the end of Torino’s STAR 1 line; 10-12 minutes of recharging are enough to keep buses in operation from 07:00 to 20:00. During charging, the two coils are just 40mm apart, allowing an efficient energy transfer. The cost for installing the inductive recharging ground system (primary coil) is about € 120 000, while the cost for installing the inductive recharging system (secondary coil) is about € 16 000 per bus, not including the cost of the battery pack (56 batteries per bus at € 20 000). The buses are 7.5 metres long and their maximum weight is 11 500kg. They travel about 130 km a day, accommodate 40 passengers and their maximum speed is 70 km/h. The 180Ah battery installed on the buses is fed at 336V and produces a power of 65kW. Operating time is 13 hours per day.
Results
Compared to diesel vehicles, electric buses provide increased comfort due to the absence of vibrations and noise, and zero-emissions within the city, thereby improving citizens’ quality of life. The electric buses are in use for longer periods of time as they no longer need to go back to the depot during the day for recharging and do not need to swap batteries.
Maintenance costs for both lines are reported to be 0,61EUR (with each bus running about 110km a day). In 2007, 565 000 passengers used the lines; in 2008, STAR 1 used eight buses; STAR 2 used seven. Based on the STAR 1 buses, energy consumption was 1,25 kWh/km.[1] A diesel bus with similar characteristics would consume, according to GTT, 4.27kWh/km, equivalent to 0.43litre of diesel.[2]
[1] Paietta P. (2013), Note sul problema dell’innovazione dei veicoli per il trasporto pubblico urbano su gomma. Politecnico di Milano - Master’s Thesis (available to download below)
[2] Sequoia automation (unknown date), K-BUS – Simulazione di performance tecnico gestionali di sistema di biberonaggio energetic a ricarica rapida di autobus a trazione elettrica (available to download below)
Challenges, opportunities and transferability
The system is user-friendly and safe: it uses available electrical infrastructure, charging is automated and possible under all weather conditions, and the primary coil is buried, meaning the system is unobtrusive and protected from dirt and vandalism. The implementation of the system does not require special conditions, simply the installation of a primary coil underground, its connection to the electricity grid, and the secondary coil in the floor of the bus.
Strong political will is necessary to secure invetment in electric bus fleets. In general, it is hard to convince municipalities to implement electric buses because of the perception that they are prohibitively expensive. However, a recent US study, which compared the acquisition and energy costs of electric and diesel propulsion over 10 years of operation, estimates that the costs of an electric bus pays off after between one to four years of operation.[3]
The inductive charging technology increases the profitability of an electric bus fleet because the more frequent, but shorter, charging cycles reduce the required battery capacity and increases its service-life. As a result, electric-bus-fleet operators can buy cheaper buses with smaller batteries. Furthermore, the more widespread plug-in technology used for charging electric buses – which requires direct contact between the charger and battery - is not well thought of for health and safety issues, despite the fact that the near-field coupling between the charging point and the receiver on the bus produces a magnetic field within the limits recommended by the International Commission on Non-Ionizing Radiation Protection.
[3] Wechlin M. (2013), Competitive and Clean Transportation. Presentation held in Geneva at the 60th UITP World Congress and Mobility & City Transport Exhibition.
Topic:
Collective passenger transport
Clean and energy-efficient vehicles
Country:
Italy
City:
Torino
Contact:
Marco Zanini
27 Apr 2015
27 Apr 2015