Plug-In Hybrids: Technology Rolls Closer to Reality

March 28, 2007

In alternative-fuel transport circles, the plug-in hybrid electric vehicle (PHEV) is the current Holy Grail. So far, no plug-in hybrids are on the US market. However, recent developments in battery technology, improved availability of conversion kits, federal research support, and pending legislation might form a "perfect storm" that could push PHEVs into car dealerships near you within the next few years.

Is this good for your local environment? That depends on where your power comes from. Could you use a PHEV without blowing your utility budget? That depends on utility rate structures and what time you tend to recharge.

Existing hybrid cars contain an internal combustion engine and a self-charging battery to power the drive train. PHEVs feature extra battery capacity, plus you can recharge them from a standard 120-volt electrical outlet. The touted advantage is that, on short trips of moderate speed, PHEVs effectively run as all-electric cars because the gas engine is not needed. Plus, battery power would be employed on all trips for as long as the charge lasts, reducing fuel costs on all trips. PHEVs can be made to run on any fuel, including diesel, biodiesel, and E85 (a commercially available 85% ethanol, 15% gasoline blend).

The downsides: So far, battery technology hasn't been able to deliver enough energy storage with snappy, responsive power delivery without a significant weight premium. Also, there are significant challenges to maintaining battery life. Decreased gas costs must be weighed against increased power costs. And finally, the net impact to the power grid and utility emissions of CO2, SO2, mercury, and other pollutants could be substantial (either positive or negative, opinions vary).

Here are some PHEV trends, sources, and resources to watch:

New battery technologies: A Mar. 11, 2007, New York Times story by Jason Pontin covered some of the latest developments and leading contenders for batteries that would suit PHEV applications (paid archive/free preview).

Right now the leading contender technology is the lithium-ion battery. All battery technologies involve massive use of toxic, caustic, and hazardous substances. When considering the environmental impact of widespread popularity of electric, hybrid, or plug-in hybrid vehicles, don't forget about battery manufacturing, recycling, and disposal. Illegal tire dumps may start to look like a walk in the park by comparison.

Battery R&D is costly, with an uncertain payoff. The US Dept. of Energy recently released its draft plan to share this risk with private industry by supporting likely "leapfrog" PHEV technologies. Comments on this plan are due by Mar. 28, 2007. The final plan is expected by Apr. 20, 2007.

The National Renewable Energy Lab's Advanced Vehicles & Fuels research program has a special energy storage effort to move battery technology for electric, hybrid, and plug-in hybrid cars forward. Ahmad Pesaran, 303-275-4441.

What are the carmakers doing? In a Mar. 12, 2007, post to GM's FastLane blog, GM Environment and Energy VP Beth Lowery recounted a webcast briefing she gave on GM's current battery R&D efforts.

At the 2007 Detroit Auto Show, GM's Volt concept car drew ample media attention. It featured a rechargeable electric drive system, and can be configured to run on electricity, gasoline, E85 or biodiesel. This concept may never get to market, but watch for vehicles based on its underlying technology, GM's E-Flex Propulsion System. More from EV World.

Ford is assisting California's South Coast Air Quality Mgmt. District's new pilot program to convert 20 of the Ford Edge cars to PHEV: Mar. 5, 2007, CalCars-News item; Mar. 7, 2007, Los Angeles Times story.

According to a Mar. 2, 2007, Reuters story, Toyota "is working on developing a plug-in hybrid vehicle and is open to joining with other automakers in battery development."

Some car owners have installed conversion kits to turn their Priuses and other hybrid cars into PHEVs. There's a risk this may violate the car's warranty. CNET review of one such kit.

  • Hybrid Owners of America, a group backed by the Civil Society Institute think tank, has more info on conversion kits and PHEV issues and news: 617-928-3408.

On the legislative side, watch for federal and state bills to offer PHEV incentives, such as tax credits to PHEV owners. Two to watch are:

Utilities are a big part of the PHEV picture, since power plants are the main emissions source for PHEVs. Increased demand for utility power would increase emissions - and perhaps demand for more power plants. But as (or if) utilities upgrade combustion efficiency, diversify fuel choices, and upgrade emission controls that net impact could decrease. Utilities also could offer rate incentives to encourage PHEV owners to charge their vehicles at off-peak times, such as at night.

On Feb. 21, 2007, Xcel Energy (a major multistate utility) issued a report on a six-month study of how increasing popularity of PHEVs could affect Colorado - a state that depends mainly on coal-fired plants. Said Xcel CIO Mike Carlson, "Depending on when customers choose to recharge, adding PHEVs to the road may help reduce overall emissions of CO2 without significant increases in utility infrastructure" (release).

One PHEV angle that's received little notice so far is the technology's potential to serve as backup capacity for the electric power grid. Sounds wild but some early studies say it might be feasible. "Vehicle-to-grid charging" would offset the higher purchase price of PHEVs by allowing vehicle owners to "provide grid power support to utilities or major power consumers" (Sept. 27, 2006, Green Car Congress article).

Beyond cars: PHEV technology could work with almost any kind of vehicle. Current experiments include trash trucks, postal vehicles, and city buses; school buses; and even tugboats.


PHEVs were a hot topic of discussion at MIT's Mar. 11-12, 2007, Energy 2.0 conference. The panel "Hybrid and Plug-in Hybrids: Driving Towards Grid Powered Transport?" included some of the top current experts in the field (agenda).

As with most fast-moving current topics, the Wikipedia page "Plug-in hybrid electric vehicle" tends to keep pace with new developments. While Wikipedia information requires verification, it is a good source of leads and does provide links to supporting references. To follow ongoing edits to this page, subscribe to this RSS feed.