Somewhere, Ferdinand Porsche is smiling. One hundred and seven years ago he introduced his Semper Vivus, a name that reflected the “always alive” capability of his new battery-powered car. Built in cooperation with Vienna’s Lohner, it had electric motors on its front wheels that were powered by a forty-four-cell battery pack. So far, just an ordinary electric car. But Porsche found a way to keep its batteries charged.

Mounted behind the front seats of Semper Vivus were two 3.5-horsepower, single-cylinder de Dion engines, each driving a generator. Under way, the generators’ output was fed directly to the front-wheel motors unless it wasn’t required, in which case it was diverted to the batteries. The latter were switched into the circuit to help the generators when needed—on upgrades, for example. An appealing feature of the layout was that the generators were operated in reverse as motors to start the de Dion engines.

Porsche’s creation was a series hybrid, in which the car’s heat engine has no direct connection to the driving wheels, as opposed to a parallel hybrid system such as that found on the Toyota Prius. The idea wasn’t original. Based on earlier trolleycar designs, Chicago’s W.H. Patton built vehicles in 1898-99 that drove their wheels by an electric motor powered with batteries that were charged by an onboard gasoline engine and generator. In 1896, both L. Epstein and H.J. Dowsing patented various combinations of these elements in Britain, while in America gasoline-electric vehicles were made by Indiana’s Munson and Illinois’s Fisher at the turn of the century.

Now, thanks to General Motors, the series hybrid is back on center stage in a big way. “Most Significant” concept was only one of the accolades given to Chevrolet’s Volt at this year’s North American International Auto Show in Detroit. Though the fourdoor sedan’s styling is crisp and chunky, this isn’t its main appeal. The fascination is under its skin, where the Volt’s front wheels are driven by a permanent-magnet electric motor capable of maximum power delivery akin to 160 horsepower. Its current comes from a 400-pound lithium-ion battery pack in a deep center tunnel between its seats.

The battery can be fully charged in less than seven hours from a 110-volt supply. Like Porsche’s Semper Vivus, however, an energy source is on board as well. In this instance, it’s a three-cylinder, twelve-valve Opel-made Ecotec twin-cam sized at only 1.0 liter with an added turbocharger to improve both power and efficiency. In what GM describes as its E-flex system, it drives a generator with an output of up to 53 kilowatts, the equivalent of 71 horsepower. The electricity thus generated is delivered to the Volt’s batteries and/or piped directly to its motor as its sophisticated controls dictate.

“The generator offers both range extension and recharging of the battery on the fly,” explains vehicle chief engineer Nick Zielinski. “If you drive the vehicle for forty miles on electric power alone, then the engine-driven generator automatically kicks in and will recharge the battery while you’re driving at a constant 60 miles per hour.” Pointing out that forty miles easily encompasses many commutes, GM vice chairman Bob Lutz says, “If you lived within thirty miles of work and charged your vehicle every night when you came home or during the day at work, you would get 150 miles per gallon.”

With his usual enthusiastic hyperbole Lutz adds, “I’ve never been as excited about anything in my nearly forty-year career as I am about this program.” However, Maximum Bob did have a preview. In 1969, during Lutz’s first stretch at General Motors, its engineers unveiled a series hybrid of considerable significance. Based on an Opel coupe, the Stir-Lec II used lead-acid batteries in the nose driving its rear wheels through a 20-horsepower electric motor.

In the trunk of Stir-Lec II was its range-extending engine, a single-cylinder Stirling producing 8 horsepower. The constant-speed Stirling was a low-emissions unit well-suited to the application. Though weighing the same as the Volt, at 3250 pounds, Stir-Lec II’s performance had much to be modest about. In the 8.5 seconds that the Volt should take to reach 60 mph, the earlier car was only doing 30. Yet it was an important step along the series-hybrid path.

What Stir-Lec II illustrated was the versatility of the series-hybrid concept. Any energy source that can recharge its batteries can be installed. Even a fuel cell would be suitable as a range extender. In 1993, Volvo showed its Environmental Concept Car with a series-hybrid drive built around 770 pounds of nickel-cadmium batteries. The ECC’s range extender was a small gas turbine powering a high-speed generator whose output could be switched directly to the drive motor as well as to the battery pack.

These earlier vehicles exemplified a virtue of the series hybrid, which is that its heat engine can run at a constant speed, the speed at which it can be engineered to operate most efficiently. This strategy, which was used in both Stir-Lec II and Volvo’s ECC, applies as well to the E-flex system used in the Volt, but with modification. Engine speeds are expected to range between 1500 and 3000 rpm depending on demand. An important advantage is that the engine is load-controlled so that it can run with an open throttle, the most efficient condition.

In many cities, you may have experienced series-hybrid motoring already. Orion, an arm of DaimlerChrysler, makes buses that use the HybriDrive system developed by Britain’s BAE Systems. This is a true series hybrid, with a diesel-powered generator delivering wattage to batteries or directly to the drive motor. Several thousand such buses are already in operation, giving lower emissions and much-improved fuel economy that compensates for their $500,000 cost. Especially in buses, the hybrid’s ability to recoup energy when braking is an important fuel-mileage extender.

As demonstrated in the Volt, the E-flex system is plugged into the architecture of GM’s global Delta platform, future-proofed for 2009 for such models as Chevrolet’s HHR and Cobalt. This is a clear indication that the Volt’s platform “has been developed for production intent,” as stated by Jon Lauckner, GM’s vice president of global program management. “This program is not a science project or a PR ploy,” he adds. “We’re very serious about taking it to production in high volume.” Before the end of this year, the first E-flex experimental mule will be on the road.

Lutz and Lauckner have a powerful ally in Mike Jackson, CEO of AutoNation. When Jackson speaks, carmakers listen, well aware of his 257 dealerships in seventeen states serving more than 600,000 customers a year. AutoNation is the world’s largest seller of Mercedes-Benz and Chevrolet cars. Jackson was so impressed with the Volt that he went out of his way to press Bob Lutz to produce it. “We can sell this car,” Jackson states.

“It can be on the market in five years.” GM says that batteries are the problem. While the nickel-metal hydride cell is the current battery of choice for hybrids, GM wants to wait for the lighter and livelier lithium-ion combination that powers your laptop. It offers triple the energy storage capacity and power density. Not until 2010 at the earliest is lithium-ion thought likely to be ready for prime time in vehicles with electric drives. The timing would be ideal for a new range of vehicles using the E-flex system.

In its first presentation of the concept in the Volt, GM styled a car that could have appeal in many markets. “We leveraged our resources around the globe to develop the design aesthetic for the Volt,” says Ed Welburn, vice president of GM global design. Although the Volt has strong Chevrolet identity at the front, doesn’t that deeply curved windshield say “Saab” to you? Wouldn’t it be great for GM to launch a new Saab model on the Delta platform and give its ecology-aware Swedish make a leading role in the global introduction of E-flex? Yes, indeed it would!