Charge electric car but don’t boil kettle, says National Grid

Electric car drivers are unlikely to be able to rapidly charge their vehicles at home at the same time as boiling a kettle, National Grid has warned. 

The operator of Britain’s electricity transmission system has cautioned that using a powerful and fast electric car charger at home will trip a main fuse if vehicle owners simultaneously utilise other “high demand” energy items, such as kettles, ovens and immersion heaters.

The warning is contained in a National Grid “thought piece” document which considers some of the potential challenges around Britain’s ambition for a mass rollout of electric vehicles. 

The government last month announced plans to ban the sale of new petrol and diesel cars in Britain from 2040, as ministers strive to comply with commitments to tackle climate change and reduce air pollution.

Carmakers are rushing to adopt zero-emission technology, with almost every main manufacturer due to release an electric vehicle capable of driving several hundred miles on a single charge by the end of the decade.

National Grid assumes in future most electric cars will need to have a battery capacity of 90 kilowatt hours (kWh) for drivers to make long distance journeys of about 300 miles. The ability to travel greater distances without stopping to recharge will be a “must have” if vehicle owners are to abandon their petrol or diesel cars entirely, it suggested. 

An average size battery charger of 3.5kW would take 19 hours to fully charge a 90kW battery even when it is already 25 per cent full, according to National Grid’s calculations. 

A more powerful 11kW device could power up, for example, a Tesla Model S with a 90kW battery in six hours if it is already 25 per cent charged, but owners would be unable to boil their kettles during that time without blowing a fuse, said National Grid. 

“The average household is supplied with single phase electricity and is fitted with a main fuse of 60-80 amps,” added the company.

“If one were to use an above average power charger, say 11kW, this would require 48 amps. When using such a charger it would mean that you could not use other high demand electrical items . . . without tripping the house’s main fuse.” 

Erik Fairbairn, founder of charger company Podpoint, said only 5 per cent of homes in Britain would be able to take a more powerful charger than 7kW. But he added this will be fast enough for most needs, as people will “only very rarely” run the electric car battery all the way down during normal daily use.

Homes could be fitted with the maximum 100 amp main fuse to accommodate more powerful chargers, suggested National Grid.

But it added that building several thousand “super fast” charging forecourts — similar to modern day petrol stations — would be preferable “rather than carry out a large scale rebuild of the domestic electricity infrastructure”.

The issue highlighted by National Grid in its thought piece document is just one of the challenges around a mass rollout of electric vehicles that have to be considered by policymakers and regulators.

Electricity distribution network companies such as SSE, which own the local wires and cables that deliver power to homes, have warned drivers are unlikely to be able to charge their cars at peak times — for example after work — if the UK wants to avoid costly infrastructure upgrades. 

Most homes will have to be fitted with smart chargers that will only power up vehicles when the grid is able to cope, they have argued. 

Green Alliance, a think-tank, estimates just six “closely located” electric vehicles charging simultaneously at times of high demand would be sufficient to trigger local power shortages.

Dermot Nolan, chief executive of energy regulator Ofgem, said in a Financial Times interview it was possible there could be different charging frameworks.

“You can see people perhaps deciding to charge at home,” he added. “Another model would be to have quasi-petrol stations, large groups of situations perhaps near a point where the network is strong, where people all charge there.”

Sales of electric or hybrid vehicles in the UK increased by 22 per cent last year to 88,919 vehicles, according to the Society of Motor Manufacturers and Traders.

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