The vehicles

Apart from the large pod on the roof at the front of the bus containing a battery pack and the radiator pack for cooling the batteries and the interior, which increases the height from 2.9m to 3.3m, the vehicles look the same as any other Wheel Forward Streetlite. A sign in the cab reminds drivers that it is 11ft 6ins high (3.5m). It is based on the 9.48m long model which, like all Streetlites, is 2.445m wide. Internally the layout is exactly the same as similar diesel buses except for an additional step at the rear of the saloon to surmount the rectifiers. Other minor differences are a different driver’s display that provides information relating to charging and battery state and some controls relating to the raising and lowering of the recharging platform. The seating capacity is the same at a maximum of 37, though the additional weight of the batteries takes the ULW from around eight tonnes to 9,720kg, which reduces the standee capacity to nine.

In place of the usual diesel engine, the Streetlite EV has a Siemens ELFA II electric drive system, as used by Wrightbus on the New Bus for London. It is equipped with the latest generation Lithium Ion batteries. Three sets are employed, two mounted on the bus behind the rear wheels and the other on the roof. Each battery string has seven modules and within each module there are seven individual cells, making a total of 147 individual cells. They are manufactured by Dow Kokam and weigh 1.8 tonnes. Mark Mitchell, product Director for Wrightbus, explained that choosing which batteries to use was always a compromise. The Lithium Manganese Oxide units had been selected because they offered the best balance of chemistry. The chemistry they employ is in the bottom third of the heat generation range and because of that they do not heat up too much during charging, while still enabling recharging within an acceptable timeframe.

Charging

Mark Mitchell explained that the vehicles are being charged by means of an induction system with charging points in Wolverton and Bletchley at either end of the route. The charging pads containing the four primary coils are set in the ground at the termini. When the bus arrives it parks precisely over the pad and, controlled by a wireless communication system, a hydraulic plate on the underside of the bus lowers into place enabling the secondary coils on the bus to pick up charge and transfer it to the on board batteries. They transfer it at the relatively high power rating of 120kW which enables recharging to take place six times faster than it would with a trickle charge system. The efficiency rate of 90% is comparable with trickle charging.

Regular ‘opportunistic’ recharging in this way means that the range can be increased and/or the batteries do not have to be as large as they would otherwise be, reducing weight and increasing passenger capacity, which remains an issue on electric buses.

The batteries are warranted by the manufacturer for five years but Wrightbus are expecting between seven and ten years from them, part of the aim of the project being to understand how battery life will evolve. Some systems still run off a standard 24-volt battery and there is also a small auxiliary diesel heater though future generations would almost certainly be all electric and have smaller batteries.

Every aspect of the vehicle performance is being monitored in detail to determine exactly how the electricity is used. The telematics system has been developed by Wrightbus from a standard 21st Century system. It monitors all manner of things including battery temperature, charge rate, efficiency of charge rate, time in charge station, battery status at different times and the temperature of every electrical component.

Mark said that the vehicle had the standard Streetlite regenerative braking system, not the micro hybrid system. That could be fitted but the saving would be much less than on a conventional bus.

I spoke to Daniel Dorflinger, CEO of iPT Technology who supplied the power charging system for the bus. He explained that his company had started with wireless power transmission in 1997 and now had thousands of installations of which perhaps ten were bus related. Previously the best known scheme had been that in Turin and Genova, launched in 2002, which utilised 25 EPT buses. These run on a wireless basis in the day and are plugged in overnight.

Daniel explained that in addition to the two termini charging stations, there will be a third one installed later in the spring at the main bus station. This is not technically needed for the trial as the two existing ones will cover the requirement, but it will be useful if more lines are added and it will also give more useful technical data. Similarly, although a back up trickle charge system is available at the depot as a back up, conceptually it is not required. ‘In theory, the bus could run without overnight charging and be totally efficient,’ said Daniel. He also indicated that to maximise the lifetime of the battery, it was preferable to stay within the 30-70% of full charge range, because if you charge over that or deplete below that there is an impact on life. In Milton Keynes they will only be charged to take what is necessary for 120% of a duty cycle. The cost of a charging station is around £200,000 depending on installation.

Daniel confirmed that it was quite safe to recharge with passengers on board because the system is fully shielded. The only electro-magnetic field is between the two coils.

He also said that while numerous bus manufacturers were using the company’s products these days, they only started doing so two years ago when it was realised that electric buses could be made economic. It is the first time that iPT has worked with Wrightbus and their first all electric and inductive bus project.

Training

To ensure driver familiarity with the vehicles, two trainers and two reserve trainers were trained to instruct the driving pool in their use. In total 34 drivers received four hours of instruction each, on a one to one basis with the instructor, though the roster for the 7 service has 22 drivers. Speaking to driver, John Tanner, he said that the big difference was how quiet they were. He also explained that there had been awareness training too, especially with regard to the centre of Milton Keynes where there were a lot of walkways, though he had not had to sound the horn yet.

During the training the buses had performed well. The only issue had been with one bus when the charging plate had gone down but refused to come back up again. This had been easily resolved. To ensure that everything went well a Wrightbus engineer had travelled with the vehicles during these early stages of the experience.

Although there will be eight Streetlite EVs on the 7, only three had been delivered and commissioned at the time of the launch. When they go into revenue earning service on 19 January there will initially be a mix of Streetlite EVs and diesel Solos with the remaining five Streetlite EVs gradually fed in.

On the road

I joined Baroness Kramer and other journalists on a trip around Wolverton on one of the buses. It is extremely quiet, indeed the level of conversation on board seemed particularly loud as a result. The ride was comfortable and the bus seemed to combine smoothness with a reasonable turn of pace.

The demands of television journalists, who need to film everything three times over, meant that we completed several laps of Wolverton before they had what they needed in the can, to use an outdated parlance. After charging three times to enable filming the batteries were perhaps rather fuller than they normally would be, though they cannot overfill because there is a cut off that prevents it. When we came to pull away the bus would not do so. Fortunately the Wrightbus team quickly established that the cause was one of four sensors on the charging plate which was not registering that the plate was in the stowed position. This was quickly remedied and away we went again, the bus appearing to have the acceleration it will need to maintain the timetable.

Environmental impact

Information available at the launch claimed that the eight buses will reduce carbon dioxide (CO2) emissions by 269 tonnes annually, and as the electricity grid becomes greener that figure will rise to 686 tonnes a year. This was the equivalent of saving 484,000 car journeys. In terms of noise emissions, a diesel is twice as loud as the electric Streetlite EV for passengers on board while for pedestrians on the street the diesel is four times louder. Apparently, if Great Britain’s buses were all to switch to electric 1,105,143 tonnes a year of CO2 would be saved rising to 2,562,966 million tonnes as the grid becomes greener.

By Stuart Jones