The EV overload

July 18, 2019 //By Steve Hughes
electric vehicle
The rise of the electric vehicle, or EV, is inevitable. Over the past decade, many car manufacturers, including BMW, Audi and of course Tesla, have blown the lid off this new technology. As EV battery capacity and motor efficiency continue to increase, the ability to charge the batteries within a reasonable timeframe is of the utmost importance.

The 2018 model of the BMW i3 has a battery capacity of roughly 38 kilowatt hours, which would take roughly ten to twelve hours to charge through a standard UK 13 amp, 240 volt wall socket. By using a dedicated charging infrastructure such as Tesla’s Supercharger network, pushing power at 150 kilowatts (kW), that time drops to less than 20 minutes. At the leading edge, chargers have been produced that provide 300 to 400 kW of power to specially designed EVs, potentially charging the vehicle entirely in five to ten minutes.

Even at that timescale it’s still not comparable to the time taken to fill a car with fuel. This inconvenience is by far the biggest hurdle facing public adoption of electric vehicles. If EVs were as quick to fuel as traditional cars, then the benefits of EVs would entirely outstrip those of conventional cars.

 

Getting the power to the car

Electrical grids are very tightly maintained systems. The system needs to respond to changes in demand within seconds. Surplus power is simply wasted, and if demand is not met areas of the grid will brown out. The sign of a quality grid is not just its capacity, but its flexibility to adjust that capacity in response to demand.

For a relatively well-known example, when the half-time whistle blows on England football games, thousands of kettles are flicked on almost simultaneously. The national grid must respond to this change in demand by, for example, patching in extra generators in power plants or releasing stored water through a hydroelectric generator.

An average kettle may have a power rating of 2 kW, meaning one EV charging through a Tesla Supercharger is equivalent to 75 kettles running for as long as the vehicle takes to charge, possibly up to half an hour. When scaled up to a fully electrified road network after rush hour, with hundreds of thousands of people plugging their EVs in as they get home from work, the problems that the grid infrastructure must face become very apparent.


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