2017 Tesla Model S
Although electric cars do not emit exhaust, it's widely recognized that the electricity to charge their batteries often still comes from fossil fuels.
This has led to the scrutiny of electric cars to determine whether their overall "wells-to-wheels" carbon footprints exceed those of regular vehicles powered by internal-combustion engines.
For most U.S. drivers, electric cars are already better, thanks to more natural gas and renewable energy powering the electricity grid.
In the United Kingdom, electric cars now have lower CO2 emissions than even the most fuel-efficient cars powered by gasoline or diesel fuel—in the summer.
It's a different story in winter, though, when more electricity is produced from fossil-fuel powered energy plants, according to The Times (registration required).
A Tesla Model S actually produces more CO2 per mile in the winter than the most fuel-efficient vehicles powered by diesel or petrol.
Offshore wind farm
In the summer, more of the United Kingdom's energy production comes from solar, wind, and nuclear sources.
But, in the winter, the UK relies more heavily on coal and natural gas-fired energy production.
Still, the situation is steadily improving even during winter months,
According to a study commissioned by Drax, a power generation company, carbon emissions for a Tesla Model S have dropped from 124 grams per kilometer driven in 2012 to 74 g/km driven during a UK winter this year.
In the summer, a Model S now creates just 41 g/km thanks to an increase in renewable energy sources.
In 2012, just 7 percent of energy production came from wind and only 1 percent from solar; coal-powered plants provided 41 percent of electricity.
2011 Nissan LEAF
Fast forward to the summer of 2017, and wind power alone produced 12 percent of the UK's electricity needs, while solar accounted for 4 percent.
The switch to more renewable energy means that every electric car gets cleaner and lower-carbon over its lifetime.
The Nissan Leaf, Britain's best-selling electric car, produces just 32 g/km of carbon emissions.
Although the reduction in overall emissions is positive, more electric cars sourcing power from the grid poses a challenge not just in the UK, but in every country with growing numbers of cars that plug in.
Electric utilities and tiered pricing plans will play an essential role in the future of electric cars to ensure they charge at optimal times—generally overnight—to reduce additional stress during peak demand periods on the grid.