Hybrid cars and the power grid

Hybrid cars and the power grid

March 13th, 2008

Today, people who care about the environment are attracted by hybrid electric cars. But in 2020, hybrid cars and trucks might represent 25% of all the vehicles in the U.S. Of course, these vehicles will need to be plugged to the power grid to recharge their batteries. A recent Oak Ridge National Laboratory (ORNL) study has evaluated the impact of hybrid cars on the power grid for various scenarios. The study concludes that ‘the 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.’ But read more…

You can see above an example of how hybrid electric cars could recharge their batteries in the future. “Solar panels would provide shade and electricity to recharge the batteries of plug-in hybrid electric vehicles.” (Credit: ORNL) Here is a link to a larger version of this illustration.

The ORNL study has been coordinated by Stan Hadley, who works for the Cooling, Heating and Power Technologies Program inside ORNL’s Engineering Science and Technology Division.

Hadley said that previous studies about the impact of hybrid cars assumed that owners will charge them during the night. “That assumption doesn’t necessarily take into account human nature. 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.”

So the ONRL study focused on a variety of scenarios. “In an analysis of the potential impacts of plug-in hybrid electric vehicles projected for 2020 and 2030 in 13 regions of the United States, ORNL researchers explored their potential effect on electricity demand, supply, infrastructure, prices and associated emission levels. Electricity requirements for hybrids used a projection of 25 percent market penetration of hybrid vehicles by 2020 including a mixture of sedans and sport utility vehicles. Several scenarios were run for each region for the years 2020 and 2030 and the times of 5 p.m. or 10:00 p.m., in addition to other variables.”

The researchers “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.”

As ORNL is part of the U.S. Department of Energy (DOE), this study should be publicly available online. It might be, but I haven’t found it. But a special issue of ORNL Review about Pursuing Energy Options contains a detailed review of it, “Giving Back: Plug-in hybrid electric vehicles may have an unexpected value (Carolyn Krause, ORNL Review, Volume 41, Number 1, 2008).

This article says that tomorrow’s hybrid cars “may not only get its energy from the grid but also may give ‘imaginary power’ back to the grid.” What exactly is this ‘imaginary power’? “According to a vision of Oak Ridge National Laboratory researchers, the car’s charger would supply the grid with ‘reactive power,’ or non-active power, to help regulate local utility voltage.”

Here are more details about how owners of hybrid cars could give back some energy to the power grid. “DOE also supports research on one way to reduce peak demands on the electric grid: deploy distributed energy resources — microturbines, fuel cells and photovoltaic panels — to provide electricity to both local buildings and the electric grid. The plug-in hybrid could be considered another distributed energy resource, but one that also stores energy.”

Of course, energy utilities have no power — no punt intended — on their customers’ behavior. “Ideally, customers would reduce their consumption of electricity at peak load times in response to market prices or a utility’s request. During hot summers, the demand for air conditioning between 2 and 6 p.m. can boost the peak load to the point that a utility must purchase power from another utility at a higher price. In sharp contrast, the grid on the same night may be so underutilized that energy is sometimes given away.”

But these companies would prefer to see people recharging their cars during nights. “Nighttime battery charging would greatly benefit generation and distribution companies, who normally see their facilities used efficiently for only a few hours each day. Local distribution grids would see a significant change in their electricity usage patterns. For example, early evening charging would probably use a higher proportion of natural gas to coal than nighttime charging, with consequent effects on carbon dioxide and other emissions.”

For more information, you should read a previous ORNL Review article, “More or Less Electricity” (Carolyn Krause, ORNL Review, Volume 40, Number 2, 2007).

Finally, I have a question for today’s hybrid car owners. Do you recharge your car’s batteries during the night or during the day?

Sources: Oak Ridge National Laboratory news release, March 12, 2008; and various websites