Will electric cars kill utility grids? No, study says.

One of the popular criticisms of electric cars is that, as more of them roam our roads and are charged in garages at night, electrical grids will struggle and fail under the pressure.

It's popular because it seems plausible--while we're all used to having electrical goods in our houses, few use quite so much power for quite so long as a charging electric car.

As is often the case, it turns out to be a misconception--electric cars are unlikely to trouble electric grids, even as far more of them hit the roads.

Navigant Research suggests that part of the misconception comes from misunderstanding just how little energy electric cars use--and therefore require when charging.

According to the Energy Information Administration's Residential Energy Consumption Survey, the average U.S. household consumed 11,321 kilowatt-hours (kWh) of electricity in 2009.

Using average fuel consumption of 24 mpg, a gasoline vehicle doing 12,000 miles a year is even more energy-intensive--consuming the equivalent of 16,000 kWh.

If electric vehicles were that inefficient, they'd more than double a home's energy requirements. Doing that with every household in the country--or even a fraction of the homes--would result in a massive spike in demand. Bad news for the grid.

Luckily, plug-in cars are vastly more efficient when it comes to using energy.

Over the same 12,000 miles, the typical battery electric vehicle adds just a third to home electricity demand, and the average plug-in hybrid about 37 percent. Utilities are only collecting an extra $450 to $520 a year from BEV and plug-in hybrid owners, at the average residential rate of 12 cents per kWh.

Navigant says only small changes to the grid would be required--and much of the grid has already been upgraded to cope with demand from air conditioning units during the summer.

Since feedback from plug-in charging has shown the cars are rarely charged at peak times, the increase in grid load is modest.

Real-world data from utilities has already shown that existing levels of electric cars have made virtually no impact on local grids. Last year, PG&E in California said it hadupgraded only 12 neighborhood grids out of 10,000 service checks.

The CEO of a Texas utility also dismissed any concerns back in 2012. Even given the influx of extra plug-in cars since then, it seems the utilities themselves are unconcerned.

Navigant even suggests that electric vehicles will be beneficial for utilities. They won't have to spend much upgrading the grid: local distribution transformer updates, at the most. Renewables integration helps balance load on the grid, too. And ultimately, many utilities will make a little extra money from electric car owners charging their cars each night.

Which rather begs the question: Why does everyone think electric cars will kill power grids?...