Now, Greenbang doesn’t want to sound churlish here, but when she initially read reports on new research Oak Ridge National Laboratory research bearing titles along the lines of ‘plug in hybrid vehicles could affect electricity supply’, she thought “Well, durr.” After all, if you suddenly start putting lots of cars that use electricity out on the road, then it’s pretty obvious that will mean a greater use of electricity right? Not so much science as common sense.

But Greenbang’s smugness didn’t last long. It only lasted til she read this sentence about the research:

A growing number of plug-in hybrid electric cars and trucks could require major new power generation resources or none at all— depending on when people recharge their automobiles.

Then she went from smug to vaguely confused. If you’re confused too, it’s all about time: if electric car drivers plug in at night, we’re all sorted. Only people aren’t that nocturnal. They might want to just, you know, plug in during the day. Breakfast time, maybe, or after work.

In which case, says Oak Ridge National Laboratory, this will happen:

“That assumption doesn’t necessarily take into account human nature,” said Stan Hadley of ORNL’s Cooling, Heating and Power Technologies Program, who led the study. “Consumers’ inclination will be to plug in when convenient, rather than when utilities would prefer.

Utilities will need to create incentives to encourage people to wait. There are also technologies such as ‘smart’ chargers that know the price of power, the demands on the system and the time when the car will be needed next to optimize charging for both the owner and the utility that can help too.”

If we all turn out to be after work chargers, they grid’s in trouble. If we prefer doing in the dark, turns out things are all gravy.

The report found that the need for added generation would be most critical by 2030, when hybrids have been on the market for some time and become a larger percentage of the automobiles Americans drive. In the worst-case scenario—if all hybrid owners charged their vehicles at 5 p.m., at six kilowatts of power—up to 160 large power plants would be needed nationwide to supply the extra electricity, and the demand would reduce the reserve power margins for a particular region’s system.

The best-case scenario occurs when vehicles are plugged in after 10 p.m., when the electric load on the system is at a minimum and the wholesale price for energy is least expensive. Depending on the power demand per household, charging vehicles after 10 p.m. would require, at lower demand levels, no additional power generation or, in higher-demand projections, just eight additional power plants nationwide.

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