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How to Sell Power from Electric Cars Back to the Grid

A consortium sold power from an EV fleet at the University of Delaware for this first time on April 26—and turned a profit
Mini Cooper EV



Flickr/Eneas De Troya

If not for the orange power cords trailing from their sides, the 15 Mini Coopers lined up in the northwest corner of the University of Delaware's science and technology campus might have been a scene from a BMW dealership. No other outward clues hinted that in their stationary form, these cars were driving a new business.

The electric-powered versions of the Mini Coopers are part of an effort, undertaken by the university and a consortium of partners from the private sector, to develop and deploy vehicle-to-grid (V2G) technology. It is a strategy that taps the significant storage potential of electric car batteries to help manage supply and demand on regional power grids.

Under development for several years, the project marked an important milestone Friday when it celebrated its first resale of power to the mid-Atlantic region's grid operator, PJM Interconnection.

"What is new is that today we are part of the PJM grid," said Willett Kempton, a professor in the School of Marine Science and Policy at the University of Delaware and one of the pioneering architects of V2G technology. "We are contributing to its stabilization and are being paid to do so."

Over the past two years, researchers at the university and power provider NRG Energy Inc. have been developing a two-way interface between the vehicles and the grid. The interface allows 15 cars and their corresponding charging stations to communicate with PJM and provide power when needed. This service, known in the industry as "frequency regulation," can be used to balance load on a second-to-second basis, Kempton said.

"[The cars] essentially act as batteries for the grid," he said. During periods of low demand, the batteries charge on low-cost electricity, and they can later sell that power back to the grid when prices rise during periods of high demand, making a profit, he said.

The grid benefits from the arrangement as well. It is cheaper than cycling on and off thermal power plants and can be deployed more quickly, said Michael Kormos, senior vice president of operations at PJM.

A car that earns its keep
The 15 two-passenger Mini E models were donated by BMW, which will continue to add new vehicles to the fleet through the end of this year. The cars are powered by 35-kilojoule lithium-ion batteries and have built-in converters to change the direct current used by the battery into alternating current for the grid. The two-way charger can send power at levels of 18 kilowatts.

An individual car earns about $5 a day storing and selling power back into the grid, Kempton said.

"Like a conventional power plant, we bid into PJM's market and are responsible for the power we bid," he said. "But our system is different in that it responds faster, is less costly to operate, creates no pollution and burns no fuel."

Kempton published one of the first papers on V2G technology in 1997, when he arrived at the concept while searching for solutions to the intermittency problem posed by renewable energy.

"There are plenty of devices that use a lot of power. What makes vehicles ideal is that they have very predictable patterns of use," he said. In general, people tend to drive their vehicles at the same time each day, and cars are almost always idle at night, he said.

In the future, private electric vehicles could be programmed to discharge power to the grid for certain times of the day when they are most needed and provide extra storage space by recharging from the grid when they are not. Such programs could easily be overridden in the event of a schedule change, and the battery would always be kept partially charged in case of emergencies.

The potential upshot for owners would be income that helps pay the cost of the vehicle, a discount that grows every year the vehicle is in use.

The owner of the car would essentially be leasing storage capacity to the grid operator, which in turn could use it to smooth the ups and downs of a more renewable-dependent energy supply.

Preparing for a diversified future
Balancing supply and demand is one of the most important and challenging responsibilities of grid operators, said PJM's Kormos. The problem has become increasingly complex in recent years as fleets of new wind and solar power projects have come online, he added.

"In the future, we're looking at our grid and seeing a lot more renewables, but renewables only work when the weather allows -- when the wind blows and the sun shines," he said. "Rather than trying to match generation to load, as we have in the past, [V2G technology] lets us match load to generation."

PJM has amended its rules in recent years to allow smaller power projects, such as wind or solar installations and V2G technology, to participate in its power markets, he said.

Rather than interacting with the grid individually, the University of Delaware power stations aggregate the energy available in the 15 cars into a single available resource. Upon receiving a signal from PJM, the software then siphons power from all available cars until the required demand is met.

Although a number of the cars are operational as vehicles, they are not currently being commercialized in that regard. As they are already making a profit by integrating with the grid, future use as transportation can be seen as value-added, NRG Executive Vice President Denise Wilson said. The pilot project "demonstrates that EVs can provide both mobility and stationary power while helping to make the grid more resilient," she added.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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