Milton Keynes: Wirelessly charged electric buses

Arriva operates eight Wrightbus StreetLite electric buses as part of a multi-stakeholder project to demonstrate the UK’s first all-electric route and the first UK application of inductive charging. Taking a significant step towards meeting UK emissions targets within the transport sector.

The management of the project is the responsibility of the Mitsui-Arup joint venture – MBK Arup Sustainable Projects (MASP). The collaborators are: eFIS, Mitsui & Co, Arup, Milton Keynes Borough Council, Arriva, University of Cambridge, SSE, Wrightbus, IPT-Technology, Western Power Distribution and Chargemaster plc.

The first three StreetLite electric buses arrived in January 2014 with numbers rising to eight by May 2014. Rather than being solely charged overnight at a depot, the buses are topped up wirelessly when they stop over a charging plate at bus stops at each end of their route. This enables the entire route to be electric with the buses operating all day. The buses cover a maximum range of 190 miles in one day, and around 17,000 passenger journeys are completed each week.

To wirelessly charge the vehicle, the driver positions the bus over the plate at the bus stop, lowers a charging plate that sits underneath the bus and the bus battery is charged inductively. The plate on the bus and the plate on the road don’t actually come into contact; energy is instead transferred magnetically across the small gap. The principle is based on the fact that magnetic fields can be used to create a current in a wire and magnetic fields can be transferred through air.

The bus is at the ‘rest stop’ for 13 minutes, with the induction charging lasting 10 minutes before passengers board. During this time the 120 kW induction plate provides up to twothirds of the energy consumed on the 15 mile bus route, which runs from the north to south of Milton Keynes, via the town centre.

The buses leave the depot just after 6am in the morning fully charged and can stay out all day, returning at 11.30pm. They never come back with less than 40% of battery charge remaining, which helps to maintain battery efficiency.

The buses are then ‘tricklecharged’ overnight for five and a half hours at 20 kW (the minimum charge). This balances out the batteries, which again prolongs battery life. The 20 kW minimum charge means that a new substation wasn’t required to provide electricity for the depot, something that is usually needed when a number of electric buses need to be charged at one location.

Induction charging on the bus route means that the vehicle battery can be smaller and lighter than it would have to be if it had to complete 190 miles without any opportunity charging.

Milton Keynes Borough Council has recently been successful in bidding for funding from the Office for Low Emission Vehicles (OLEV) Low Emission Bus scheme, receiving funding of £1.6 million for 11 new electric buses, plus £127,500 for infrastructure.