In the meantime, however, a handful of companies aims to put the power cord in the hands of drivers who want to transform their gas-electric hybrids into plug-in hybrids, or to replace the internal combustion innards of other cars with all-electric systems.
The businesses are touting plug-in hybrid systems that can be driven up to 40 miles on batteries alone, with average fuel economy of 100 miles per gallon. The cars use gasoline once the batteries drain.
It can cost more than $10,000 to install a plug-in hybrid system on a Toyota Prius. Is the limited electric driving range worth the expense?
Absolutely, according to Felix Kramer, founder of CalCars, which counts nearly 200 plug-in hybrid conversions around the country. The Palo Alto, Calif.-based nonprofit in 2004 converted the first Prius with batteries that power up from an electrical outlet.
The range of 40 miles or less, likely to expand as battery makers race to make advances in the years ahead, covers most small trips Americans make in a day, he said. Therefore, Kramer views plug-ins as an ideal second car for commuters who still want to roll out the SUV for a weekend getaway.
"A conversion gives them the opportunity to say, 'I'm driving the world's cleanest extended-range vehicle,'" he added. And early adopters will pay a premium for the plug-in option, as they do for luxury extras, such as leather seats, that offer no economic payback.
Kramer believes that car makers will give their blessing eventually to qualified vehicle modifiers to install plug-in systems. For now, a small but growing collection of mechanics and dealers around the country will perform the service.
Among the choices already available to consumers, Plug-In Supply is making conversion kits based on an open standard from CalCars.
The Petaluma, Calif., company is selling $5,000 conversions that enable a Prius to drive a maximum 20 miles on full, lead-acid batteries, or $11,000 with lithium-iron phosphate batteries. Professional installation takes a day or two and costs about another $1,000.
The battery chassis can be installed on hinges to sit handily above the spare tire compartment, although adding the heavy lead-acid kit also requires boosting the car's shocks. By contrast, $10,000 conversions from competitor A123 Hymotion of Watertown, Mass., nestle lighter nanophosphate lithium-ion batteries inside the spare tire compartment.
Drivers can charge up by connecting a power cord from an exterior panel on the Prius to a 110-volt outlet, then waiting 8 hours or less.
Plug-In Supply has shipped 30 systems, and a factory in San Jose, Calif., should produce enough kits to ship two per day later this summer, according to founder Robb Protheroe.
He's seeking $5 million in venture funding to expand and attract a following before the Chevy Volt plug-in hybrid is due to roll off assembly lines late in 2010.
Protheroe described having a backlog of 75 orders and said a dozen dealers are signing up to install his systems in California, Illinois, New Mexico, New Jersey, Texas, Florida, Washington, Oregon as well as in Italy, Australia, Canada, and Germany.
"Texas is wide open right now," said Bill Kelly, who is working to establish Protheroe's plug-in conversions at an auto service center in Plano, Texas. "A lot of people are scratching their heads trying to figure out why they bought their SUVs."
Installers of Protheroe's equipment include the solar-powered, female-owned Luscious Garage, which caters to hybrid owners in San Francisco, and plans to add a space for plug-in electric hybrid conversions.
Another shop in San Francisco, Pat's Garage, has serviced hybrids since 1999. Owner Pat Cadam has been performing A123 Hymotion plug-in conversions for more than a year.
"We both share in the idea that the more of these cars that are on the road, the better," he said.
Cadam doesn't believe that electric cars will come to mass market until around 2012. Toyota's 2010 plug-in hybrid plans, he noted, are limited to a run of several hundred vehicles for fleets only.
In the interim, Cadam sees expanding the number of plug-in cars as crucial to whetting the public's appetite for electrified cars.
A123 Hymotion's other approved plug-in conversion facilities include Seattle's Green Car Company and four Toyota dealerships in Boston, Los Angeles, Minneapolis, and Washington, D.C.
The kit maker, owned by battery company A123 Systems, which is filing to go public, said it has begun shipping consumer-ready systems, with the majority of orders to ship by the end of this year.
Utility Pacific Gas & Electric and Google are among the high-profile Hymotion testers. Employees at Google's Mountain View, Calif., campus found the plug-ins achieve an average 93.5 miles per gallon. (The search giant's RechargeIT initiative gave $2.75 million to electric-car start-up Aptera and battery maker ActaCell in July.)
However, the safety of plug-in hybrids came into question in June when a Prius converted by Hybrids Plus of Boulder, Col., burst into flames. That setup used battery cells from A123 Systems, but not the same kind found in its plug-in conversion kits. A third-party investigation blamed improper assembly for the fire.
A123 Hymotion insists that its crash-tested product will disconnect a battery pack automatically in the case of an impact, and meets federal safety and emissions standards. Both that company and Plug-In Supply offer 3-year warranties and assure consumers that a conversion won't void a Toyota warranty, unless plug-in alterations directly cause a failure.
Protheroe suggested that the added plug-in batteries allow the original Prius batteries to rest, perhaps extending their life.
Kim Adelman, who aims to sell plug-in installations by November, considers his use of nickel metal hydride batteries - the same brew used in the Prius - an advantage over systems with high-density lithium-ion batteries, which can be unstable if punctured in a crash.
"Safety is No. 1, of course," he said. "No. 2 is making emissions better and using less gas."
Adelman's company, Plug-In Conversions near San Diego, has 20 potential Prius owners waiting to pay between $9,750 and $19,750 to enable an electric-only range of between 8 to 30 miles.
Other passenger car conversion companies in California that appear to be in early stages of development include OEMTek and EnergyCS.
More-expensive, all-electric makeovers are also available. For $55,000, AC Propulsion of San Dimas, Calif., will convert a Scion xB to run up to 95 miles per hour, lasting 150 miles per charge.
Some consider converting gas-guzzling road hogs more important than focusing on compact or hybrid cars that are already relatively green. Former Intel chairman Andy Grove called in July for electrifying 10 million large vehicles in the United States in the next four years.
In that spirit, engineers led by professor Eli Emadi of Chicago's Illinois Institute of Technology gutted a Ford F-150 truck to install a plug-in hybrid system meant to increase fuel economy from 16 to 41 miles per gallon.
"We are targeting pickups, SUVs and vans - that's the really big market," said Emadi. "If you start with a gas guzzler that gets 12 miles per gallon or a school bus that gets 7 miles per gallon and increase that, the impact is far bigger."
His team "hybridized" the Ford's conventional drive train and then turned it into a plug-in hybrid. Nickel metal hydride batteries take up to 5 hours to charge and enable the truck to run without gasoline for 15 miles. That adds about 15 percent of the vehicle's weight to the body but also improves its torque, he said.
Emadi has spun off the technology into Hybrid Electric Vehicle Technologies, and plans to produce up to 50 more conversions at $60,000 each by 2009. He said that scaling up the technology, with a hoped-for infusion of $5 million in venture capital, should sharply cause a price drop by 2010.
And Andy Frank, known as the inventor of the plug-in hybrid, has spun-off his technology by licensing it to Efficient Drivetrains, a Palo Alto conversion company.
Evangelists of electrified, hybrid cars argue that although costs need to come down to accelerate adoption, other technical hurdles are less daunting.
Improved battery technologies are key to expanding the electric driving range, but today's storage capacity is good enough for the majority of trips, some claim.
Those who doubt the viability of electrified cars point to the lack of a public charging infrastructure, which start-ups Better Place and Coulomb are trying to address. Yet, advocates of plug-ins say the infrastructure to charge the cars already exists in the form of 110-volt outlets found in nearly any building. And some hope that if drivers plug in only at night, tapping into unused energy from the electrical grid, then adding new power plants will be unnecessary.
Plug-in hybrids have entered the national political spotlight, as politicians praise the potential for lessening the nation's dependence on foreign oil. Those behind electrified-car start-ups hope that government support will arrive with the next administration in Washington, D.C.
Democratic presidential candidate Barack Obama in August proposed offering a $7,000 tax credit to Americans who buy plug-in hybrids as well as loans of $4 billion to makers of efficient cars. Republican opponent John McCain called in June for a $5,000 consumer tax credit for buying zero-emissions cars and a $300 million prize for a battery maker to advance electric car technology.
"No matter how it turns out I think we've had an effect on automakers," said Adelman of Plug-In Conversions. "The feeling is just like we had with personal computers in the 1970s. We knew it was gonna change the world, and in this case it has to."