Can plug-in hybrid electric vehicles keep the electric grid stable?

Speakers at an IEEE-USA symposium on plug-in hybrid electric vehicles debate the promises and challenges of vehicle-to-grid (V2G) technology

4 min read

Google, a former CIA director, the Natural Resources Defense Council, a U.S. senator, and the IEEE aren’t often found together in the same room.

But the promise of plug-in hybrid electric vehicles (PHEVs) aligns the stars in unexpected ways. The result of their meeting on 19 September is an early glimpse at a future with vehicles powered by electricity, emitting far fewer greenhouse gases than those of the last century—and playing a key role in the very stability of the nation’s electric grid.

Organized by IEEE-USA, the ”Plug-In Hybrids: Accelerating Progress” symposium was held on a beautiful day in Washington, D.C. A full slate of presentations blended lofty phrases (”Revolutionizing the energy paradigm”) with hard-core technical concerns (Can automakers work with electric utilities to set standards?).

Into the Policy Fray

The keynote speaker, Senator Maria Cantwell (D-Wash.), plunged directly into the policy fray. ”Many of us on Capitol Hill see the potential of plug-in hybrids,” Cantwell said, describing a bill she has introduced to encourage early production and purchase of plug-ins. It includes tax credits for consumers who buy or convert to plug-ins, tax incentives on tooling for carmakers who sell early models, and incentives for utilities to offer discounts for off-peak car recharging. It also encourages utilities to upgrade to ”smart grid” technology, allowing electric appliances (for this purpose, a plug-in hybrid is a power-using appliance!) to communicate with the grid and charge themselves based on real-time power prices.

Next up was Jon Wellinghoff of the Federal Energy Regulatory Commission, who coined the term ”cash-back hybrid,” which clearly describes the benefit to consumers of plug-ins that not only charge themselves when demand is lightest and prices are lowest, but supply energy services to the grid as well. Collectively, Wellinghoff proposed, the batteries in millions of PHEVs could provide five distinct benefits: lowering greenhouse-gas emissions, improving urban air quality, saving consumers money, bolstering power-grid reliability, and reducing oil imports.

How would those results be achieved? By making the energy stored in plug-in hybrids an integral part of the grid, using a few percent of each battery’s energy storage capacity to meet peak demand rather than adding new generating capacity—and by paying consumers accordingly.

The notion is called vehicle-to-grid power, or V2G, and its workings, economics, and practicalities were the meat and potatoes of the symposium. Wellinghoff’s model appeared to show the energy cost of a plug-in hybrid falling toward zero over time. Much discussion, and some derision, ensued.

”A Faster Horse,” or Cars on the Grid?

Clearly such a notion requires radical thinking. Whether consumers are ready to make that kind of leap—let alone the automakers or the electric industry—is open to debate. But the ghost of Henry Ford was invoked, with his legendary quotation on responding to consumer demands: ”If I’d asked my customers what they wanted, they’d have said a faster horse.”

From the viewpoint of carmakers and consumers, one key concern is battery life—and the potential cost of replacing a 20-kilowatt-hour battery pack halfway through a car’s 10-year life.

After safety, the longevity of the batteries in a plug-in hybrid is the greatest unknown. Can a plug-in hybrid’s battery pack retain the bulk of its energy capacity over 10 years of daily use and more than 4000 full-discharge cycles? (For a deeper look at the challenges facing plug-in hybrid batteries, see ”Lithium Batteries Take to the Road”.) As Don Hillebrand of Argonne National Laboratory, in Illinois, said tartly, ”Batteries are the showstopper.”

Periodic demands from the grid, even for only a small fraction of the battery’s stored energy, would clearly affect the cells’ life span—but no one has data on how much. Another open issue is the development of creative financing models for replacement battery packs costing several thousand U.S. dollars even after mass production is achieved.

Third-party battery leasing could be one answer, if combined with a secondary market for batteries whose performance has fallen below automotive levels. Carmakers, electric utilities, and large consumer-financing groups are quietly batting around these notions to see if they can build a financial model that makes sense for all three parties.

Here’s one scenario: suppose you bought or leased your plug-in hybrid just like a regular car—except that your local power company actually owned the battery, charged you a set rate to recharge it, and paid you back when it took some energy out through the grid? That activity would all appear on your monthly electric bill. If your battery performance fell below a certain level, the utility would pay for a new one—and then rack the used battery with thousands of others, obtaining one thing the grid has never provided on any scale: distributed storage capacity for energy, particularly for variable natural resources such as wind and solar energy.

Electric Utilities + Google + Government = Big Challenges

During the day of lectures and debate, the engaged audience asked detailed questions of every presenter and panelist. Study data and projections from modeling exercises appeared on PowerPoint slides, sparking new questions and side conversations. The IEEE-USA plans to publish full transcripts of the day’s events in a future Proceedings . Meanwhile, a few highlights can convey the wide ground that was covered:

Google now loans six plug-in Toyota Priuses to its staff, with plans to provide 100 altogether.

Pacific Gas & Electric Co. of San Francisco is developing pricing to encourage off-peak vehicle charging.

R. James Woolsey, former director of the Central Intelligence Agency, views electric vehicles as one way to help ”destroy oil as a strategic commodity.”

Hymotion, a technology company in Toronto, is putting its PHEV conversion kit, in a Prius, through the full array of U.S. certification, safety, and emissions tests required for all new vehicles.

In the end, panelists and audience agreed, the promise of electric vehicles—to reduce oil consumption and stabilize the grid, among many benefits—demands both technology and policy advances.

That technology is under intense development all over the globe, from lithium-ion batteries to ever more sophisticated hybrid power-train control software. But Washington, where the symposium took place, is the seat of government for the world’s largest and most influential auto market. All eyes turn to policies that emerge from Washington, for they have a great impact on any car designed for this century.

About the Author

John Voelcker is the automotive editor for IEEE Spectrum. He has covered automotive technology for Wired , Popular Science,, and various National Public Radio programs. Beyond auto journalism, he consults on business strategy and product development for interactive media.

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