Is your bus ride charged?

Cleaning up public transport networks

By Antoinette Price

Power tools, mobile phones and tablets, wearables, electric toothbrushes, industrial applications powering wind turbines and equipment used in agriculture and forestry, marine, process automation and healthcare are just some of the items which can be charged using wireless or induction charging systems. Buses have joined this long list with more cities trialling this technology in a bid to make their transport systems cleaner and more efficient.

Aggie bus
Induction charging bus, Utah, US (Photo: Utah State University)

The future is wireless

Though wireless charging was developed decades ago, low efficiency restricted it to industrial uses like for robot vehicles and cranes. The technology has developed and works through electromagnetic induction, which allows an energy transfer efficiency of 90% or higher. A magnetic field generated by an alternating current in a primary coil induces a current in a nearby secondary coil. In the case of stationary wireless charging - a short-term solution - the bus on-board induction loops lowered to a few centimetres above the coil in the ground enter the magnetic field and the resulting current tops up the batteries enough to make it to the other end of the route for its next charge up. From Germany, Great Britain, to Italy, Spain and the US, electric buses charge their batteries from underground induction coils located at the start or end terminals or at some stops along the way.

Smaller is better, safer, cleaner

There are a number of advantages to this system. Drivers no longer need to find a charging station to plug into, removing the hassle and dangers that could occur with cables. In Utah, US, a federal grant has funded a bus which runs through the Utah State University Campus, powering up at the end stop. The induction charging battery is a quarter the weight of those that recharge with cables. These buses need less on-board energy storage and can be lighter and easier to produce in terms of design.

Other states are testing this technology which offers a pollution-free transport solution.

Next step: powering up on the move

Making the leap from stationary to charging on the move is the longer term goal for wireless charging vehicles. KAIST University in South Korea has the largest scale demonstration of dynamic wireless charging for vehicles. Utah State University has also begun building an electric vehicle and roadway research facility, the first of its kind in the US, which will include a large research building and an electrified quarter-mile (.40 km) oval test track to further develop this technology and its broader integration into transport networks.

Despite the benefits, research is still ongoing in relation to potential hazards of the magnetic field on the environment, and people who may be carrying metal coins or have pacemakers, which could heat up. In terms of the technology, one of the biggest challenges is to improve the efficient transfer of energy from the charging unit on the ground to the moving vehicle.

Charging ahead

Researchers are working towards a day when base charging units would be laid just below road surfaces and allow drivers to recharge on the move. This in turn would avoid the need to stop to recharge. It would supplement recharging stations allowing for small regular charging. It would also reduce battery and vehicle size, weight and production cost.

IEC Subcommittee (SC) 21A: Secondary cells and batteries containing alkaline or other non-acid electrolytes, prepares International Standards for batteries used in mobile applications and electric vehicles, as well as for large-capacity lithium cells and batteries. These Standards concern tests and measurements, design and manufacturing recommendations as well as safety requirements and are essential for the battery industry as it develops new products and chemistries.

Aggie bus Induction charging bus, Utah, US (Photo: Utah State University)
diagram of a bus How induction charging works (Photo: BBC)
bus track Induction charging track for bus (Photo: Conductix.comPreviousNext Loading)