In the days when long distance express trains were pulled by steam engines, Britain’s railway operators competed with each other to provide the fastest service. The LMS and LNER companies both ran trains from London to Scotland and there was an intense rivalry, with each trying to offer the shortest journey times. Often, trains would have limited stops or, in some cases, they would run non-stop to save time. However, there was a big problem in that the locomotives needed huge amounts of water to turn into steam. They could carry sufficient coal to burn, but not enough water and yet stopping to refill their tenders would considerably extend their journey times. The problem was conveniently solved by introducing troughs between the rails that could supply water to a locomotive while it was still travelling at speed. These troughs were typically several hundred yards in length and, as the train approached them, the crew would lower a scoop into the water of the trough; the forward motion then forced the water upwards into the tank of the locomotive’s tender. In this way, the engine received several tons of water without stopping.
The railway water trough was first introduced in 1860, but fast forward to the present time and consider if a similar concept could be applied to electric vehicles running on motorways. Instead of filling a steam engine’s tender with water, a vehicle’s battery would be recharged with electricity. Instead of a scoop to pick up water, the electric vehicle could use an appropriate mechanism to capture energy. Whilst this might sound rather implausible, it is definitely possible to conceive methods for achieving such objectives. For example, a length of motorway hard shoulder could be equipped with conductive tracks embedded in the tarmac, rather like those used with model Scalextric racing cars. Vehicles could then lower a pair of spring mounted conductors to come into contact with them. If embedded over a distance of several miles, and by having a suitable speed restriction, the vehicle could achieve an appreciable degree of charging without stopping.
While this suggestion may sound rather implausible, the possibility of achieving dynamic charging of electric vehicles has, in fact, received quite a lot of attention in recent years. Better still, the currently preferred methods do not even require any direct physical contact between the vehicle and the underlying charging apparatus. Charging is performed inductively and electricity is transferred across an air gap from one magnetic coil in the charger to a second magnetic coil fitted to the vehicle. For example, a few years ago, the US semiconductor company Qualcomm developed, built and demonstrated a wireless charging system that could dynamically transfer energy to an electric vehicle at up to 20 kilowatts while it was travelling at speed on a motorway. More recently, the European company, ElectReon AB has successfully managed to dynamically charge a fully electric 40-tonne lorry and trailer wirelessly at a test facility near Stockholm. This was achieved using coils placed under the road, at the centre of the traffic lane, which sent power to a receiver mounted under the vehicle’s chassis. A communication system was also used to provide a real time link with the vehicle.
While dynamic charging could make a significant contribution to extending electric vehicle range and to reducing long journey times, it seems that its widespread application may be limited by two important factors. Firstly, battery performance is continually being enhanced, so that new electric cars have extended ranges compared to even their more recent predecessors. In addition, the latest batteries, when coupled with advanced chargers, can be re-energised much more quickly than previously, reducing the down time needed on a journey. Also, and perhaps most importantly, the significant cost of installing the requisite charging infrastructure in both roads and vehicles is a major negative economic consideration. It seems, therefore, at least for the immediate future, that dynamic charging is unlikely to find widespread application.
Fortunately, the same inductive charging technology can be more cost effectively applied to stationary vehicles and thus there may well be a substantial opportunity for its use in places where vehicles are parked for some time, but then need to move at short notice. Examples here include car parks and taxi ranks, especially those at airports. To evaluate this idea, a £3.4 million scheme was recently announced for the City of Nottingham in which ten electric taxis will each be equipped with a wireless charging capability as part of a six-month trial of taxi rank-based charging. The UK government is supporting this initiative because installing wireless chargers at taxi ranks enables drivers to recharge while waiting for passengers, rather than having to divert to a charging station between jobs. As the technology allows for shorter and more frequent bursts of charging, it could also benefit cars with smaller batteries, where range anxiety can still be a major issue.
This is just one example of the progress being made as the world continues its transition from internal combustion to electric powered transport.
Written by Martin Goosey, Envaqua Research Ltd