The Green Alliance says the United Kingdom will have problems if it doesn’t upgrade its energy networks as EVs and solar panels become more popular.

Ini a new report, the think tank says if the UK doesn’t improve its networks by 2020, the increasing popularity of plug-in vehicles and solar panels will lead to power problems. Green Alliance says if battery-powered cars are clustered together, 1 percent of the UK could see drops in voltage. That would put electric equipment at risk for damage.

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The think tank’s report says that even six EVs parked near each other could lead to a brown out.

That’s because, according to the report, charging an EV uses as much electricity as a house does in three days, and too much of that demand at a local level could damage unreinforced networks.

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Local officials called on EV owners to try not to charge at peak times. Additionally, there’s a call for so-called “smart” chargers, which stop charging once the battery is full. Few of the more than 12,000 chargers in the UK are “smart.”

Green Alliance says that if more smart chargers aren’t installed by 2025, up to 700,000 customers could be at risk of power loss.

“The government should say all chargers from now on must be smart. Once they’re in, it’s very expensive to retrofit them,” Dustin Benton, the author of the report, told The Guardian.

It might not be panic time yet – network operators say that as worrisome as the clusters are, they have yet to have experienced any problems. Still, Green Alliance notes that EV sales were up over 50 percent in 2015, with more growth likely as sticker prices drop, and it’s the same story with solar panels.

Green Alliance made a few recommendations, such as a proposal for a new independent system design that would be separate from the current network, which is run by National Grid. National Grid, for its part, claimed it will be ready for the future.

“Growing use of solar power and electric cars will change the way the energy system is managed, but National Grid has been consistently dealing with evolution in the energy sector for decades, and these latest changes also present great opportunities,” said a spokesperson. “For example, electric vehicles can be used to help feed energy back into the system at key times, while solar power will play a crucial role in providing clean energy as coal-generated power stops being used.”

The Guardian