A dramatic growth in electric vehicles on Britain’s roads could see peak electricity demand jump by more than the capacity of the Hinkley Point C nuclear power station by 2030, according to National Grid.

The number of plug-in cars and vans could reach 9m by 2030, up from around 90,000 today, said the company, which runs the UK’s national transmission networks for electricity and gas.

The impact of charging so many cars’ batteries would be to reverse the trend in recent years of falling electricity demand, driven by energy efficiency measures such as better refrigerators and LED lighting.

If electric vehicles were not charged smartly to avoid peaks and troughs in power demand, such as when people return home between 5pm and 6pm, peak demand could be as much as 8GW higher in 2030, National Grid said.

Shifting the charging of cars to times when demand is lower would reduce the extra peak demand to 3.5GW, a smaller amount but still a similar capacity to the new reactors being built at Hinkley Point in Somerset.

The forecasts are contained in the grid’s Future Energy Scenarios report, published just days after Volvo said all its new cars would be electric or hybrid from 2019 and France pledged to ban sales of new petrol and diesel cars by 2040.

“Electric vehicles are coming – how quickly is the question,” said Roisin Quinn, head of strategy at National Grid, adding that she expected battery-powered car sales to take off in the mid-2020s.

While there was uncertainty over when falling electricity demand would be reversed, she said: “It’s a big moment when demand starts to go up again.”

National Grid acknowledged the cars’ batteries could also provide services and return power for the grid at a time when managing the network is becoming increasingly complex as variable sources of wind and solar power grow.

But it cautioned that there was “still debate over whether it will become commercially viable to flow electricity from a vehicle back onto the network to provide network services”.

Quinn said a large share of power from renewables had “already become a reality”, and three of the report’s four scenarios predict that solar power will have the biggest share of generation capacity by 2050.

In all of the scenarios, new nuclear power stations are assumed to be built and the capacity of interconnectors that provide backup power from Europe rises from 4GW now to between 10GW and 19GW in 2030.

Fracking for shale gas is expected to produce zero gas in two of the greener scenarios. However, in one scenario of high fracking, shale gas is projected to provide 32bn cubic metres by 2031, a similar amount to the 36bn cubic metres the North Sea provided last year.

Regardless of how much of the UK’s gas comes from fracking, National Grid sees gas as playing a key role in power and heating for decades. It is not until 2050 in some of the group’s scenarios that alternative, electric heating technologies such as heat pumps begin to overtake gas for keeping homes warm.

“The story around gas is that it’s critical to our supply now and will continue to be in future,” said Quinn. “We see it as having a long-term role as a reliable, cost effective and flexible energy source, and it will be favoured by many consumers.”

But with North Sea gas production declining, National Grid expects the UK’s dependence on gas imports to continue for decades, to some degree. More liquefied natural gas is also expected to be shipped to the UK in the future.

Climate change could also pose new challenges, with the UK forecast to get hotter. As temperatures warm, the use of air conditioning in summer could cause peak electricity demand to reach the levels normally seen in winter.

National Grid did not take a view on the costs of the scenarios in the report, which was published just a day after a consumer group accused energy networks, including National Grid, of earning £7.5bn in unjustified profits over an eight-year period.