Yesterday we covered the new green production cars at the 2010 Geneva Motor Show, now underway in snowy Switzerland. Today, we get to cover the cooler, sexier side of the show: concept cars!

So, here's our roundup of notable green and advanced-technology concept cars at Geneva.

Audi A1 e-tron design study live in Geneva. Photos © United Pictures, Int'l.

Audi A1 e-tron design study live in Geneva. Photos © United Pictures, Int'l.

Audi A1 e-tron concept

It seems safe to consider Audi's conversion complete. The company whose U.S. head called buyers of electric cars "idiots" only a year ago has launched the third model in its series of e-tron electric-car concepts at Geneva, all of them headed for low-volume production.

Their latest e-Tron is based on the A1 mini-car also launched at the show; it's an extended-range electric vehicle with a far smaller lithium-ion battery pack than the two e-Tron electric supercar coupes, which are based on the R8 and upcoming R4.

The front wheels are driven by a 76-kilowatt (102-hp) electric motor, and its pure electric range is quoted as 31 miles. Then a range-extending rotary engine kicks in to power a generator that powers the engine for an additional 124 miles.

Audi limits top speed to 81 miles per hour to preserve battery life, and quotes a 0-to-62-mph acceleration time of 10.2 seconds.

We'll write more on this unusual plug-in car separately. For now, it's our favorite concept. Stay tuned.

Ferrari 599 HY-KERS vettura laboratorio

Rumors began last summer, and now Ferrari has released the first complete concept showing its hybrid system in a 599 GTB Fiorano body. It claims a reduction in carbon dioxide (CO2) emissions of as much as 35 percent compared to the standard model.

The Maranello company uses a lithium-ion battery pack of unspecified size built into the floor of the car, though it claims no compromise in cabin room or luggage space.  The car's center of gravity is actually lower, and front-to-rear weight distribution remains the same.

A compact 75-kilowatt (100-hp) electric motor bolts onto the rear of the seven-speed dual-clutch gearbox used in its Grand Prix race cars. It adds torque to the 6.0-liter V-12 engine under acceleration, and can also operate on electricity only in low-speed urban driving.

The motor sends torque through a clutch to one of the transmission's two primary shafts. It also acts as a generator to recapture energy from braking, using it to recharge the battery. Accessories including power steering and air conditioning are fully electric, to operate even when the engine is switched off.

While the Ferrari hybrid is far from production ready, the company notes that it offers one potential path for energy savings in the future and it expects to apply the system to all of its models, whether V-8 or V-12, front- or mid-engine.

2010 Lotus Evora 414E Hybrid Concept

2010 Lotus Evora 414E Hybrid Concept

Lotus Evora 414E Hybrid

British firm Lotus Cars is known for building light, lithe, minimal sports cars, but its Lotus Engineering arm consults for carmakers all over the world and develops technology of its own. Now, both groups have come together to build a concept car.

The Lotus Evora 414E Hybrid is named for the total of 414 horsepower provided by a pair of electric motors that drive each rear wheel independently. The traction control system can vector torque to each rear wheel as needed to maximize stability.

Each motor puts out 295 foot-pounds of torque, resulting in 0-to-60-mph acceleration times that Lotus expects will be below 4 seconds. That's right in Tesla Roadster range. Drivers can also play with a "pseudo sports mode" system simulating a seven-speed paddle shifter.

The pair of motors are powered by a lithium-ion battery pack that is recharged by the 1.2-liter, three-cylinder Range Extender engine-and-generator set designed by Lotus Engineering and revealed at last fall's Frankfurt Motor Show.

Lotus says all-electric range is a commute-friendly 35 miles, plus another 300 miles using the range extender. Recharging is possible at any household outlet, similar to the 2010 Chevrolet Volt.

The Evora 414E Hybrid also features the Lotus HALOsonic vehicle sound generators, which are meant to improve pedestrian safety by directing sounds outside the vehicle while keeping it silent inside.

2010 Mercedes-Benz F800 Style

2010 Mercedes-Benz F800 Style

Mercedes-Benz F800 Style

The F800 Style is a forward-looking four-door coupe that accommodates two different drivetrain technologies. It is being shown as a plug-in hybrid that offers 18 miles of electric range, as well as a hydrogen fuel-cell variation, both powered by electric drive motors.

The plug-in hybrid system on the F800 will be offered as a pricey option on the next generation S-Class in 2012. It pairs a 300-hp V-6 of unspecified size with a 80-kilowatt (109-hp) electric motor that's built into the front of the company's 7-speed automatic transmission.

That combination provides 0-to-62-mph acceleration of just 4.7 seconds in the F800 Style, along with a top speed of 155 mph. Mercedes-Benz quotes speeds up to 75 mph on pure electric power. Its all-electric range is said to be 18 miles.

Proton Country concept, 2010 Geneva Motor Show

Proton Country concept, 2010 Geneva Motor Show

Proton Concepts

Malaysian automaker Proton doesn't sell in the States, but it has big ambitions in Europe. From making adaptations of older Mitsubishi vehicles, it plans to jump straight into electric-drive vehicles powered by lithium-ion battery packs.

Its trio of Geneva concept mini-cars were designed by none other than the great Italian design house Italdesign, and they feature the same Lotus Range Extender as the Evora 414E Hybrid concept (above). Electric range is expected to see several miles.

The cars are a three-door hatchback called "Country," a five-door concept with four seats, and a mini-crossover with higher ground clearance. All three are said to offer the interior space of a larger compact car within the footprint of an urban mini-car.

Opel Flextreme GT-E

General Motors plans to use the powertrain of the 2011 Chevrolet Volt, its upcoming extended-range electric vehicle, in various vehicles across the globe. Its Opel Flextreme concept is the fourth concept using Voltec mechanicals, and it's a larger car than the compact Volt.

At more than 15 feet long, the Flextreme GT-E boasts a drag coefficient of just 0.22, better than any production car today. Low rolling resistance is key to maximizing the range of electric vehicles, and the Flextreme has the same 40-mile electric range as the Volt, along with more than 300 miles from its range-extending engine.

It also has a top speed of 120 miles per hour, indicating its sporty sedan persona--as does the "GT-E" name. While its 0-to-62-mph acceleration of about 9 seconds is hardly Tesla material, the slippery shape speaks "performance" even if the loud pedal doesn't.

To achieve such low drag, the handles of the rear-hinged doors are replaced by light sensors that open the door when covered by a hand. As is often the case on show cars, rear-view mirrors are replaced by small cameras at the base of the windshield pillars.

At speeds above 30 mph, the Flextreme GT-E changes shape, extending a vertical "side spoiler" along the body side from a slot behind each rear wheel-arch.  The panels guide airflow past the tail of the car, cutting turbulence at a critical area.

The Flextreme concept has lightweight carbon-composite body panels, polycarbonate windows, and structural components built of aluminum alloys. Against the usual construction, these materials cut weight by 40 percent, again in the service of extending its range.

Porsche 918 Spyder Concept

Porsche 918 Spyder Concept

Porsche 918 Spyder Concept

The stunning 918 Spyder from Porsche was a surprise, and a very welcome one. Green-car fans liked its efficiency, while car buffs all over the world drooled over its looks--and the tantalizing possibility that Porsche might get back into the supercar game.

A 500-horsepower, 3.6-liter V-8 engine doesn't sound very green, but Porsche says the 918 Spyder can acheive 78 miles per gallon on the European cycle. (As we say, over and over, take all plug-in hybrid fuel efficiency numbers with a very large grain of salt, please.)

And it's definitely a supercar: 0-to-62-mph acceleration of 3.2 seconds, top speed of 198 miles per hour, and faster lap times around the Nurburgring than Porsche's previous Carrera GT.

The V-8 drives the rear wheels through a seven-speed direct-shift gearbox, with an electric motor contributing torque as well. A second motor powers the front wheels, with the pair of motors adding another 218 hp to the mix.

So where does that 78 mpg come from? There's an E-Drive mode that lets the 918 Spyder drive up to 16 miles on pure electric power, enough to get it in and out of anticipated zero-emission zones in European cities. Not at 198 mph, naturally.

Three additional modes--Hybrid, Sport Hybrid, and Race Hybrid--tune power delivery for increasing degrees of performance and speed. In Race Hybrid mode, the driver can push a button to add electric boost into the mix for overtaking.

As well as the 918 Spyder, Porsche showed off the production version of its all-new 2011 Porsche Cayenne S Hybrid sport-utility vehicle, and the 911 GT3 R Hybrid race car, which uses a different, flywheel-based Kinetic Energy Recover System similar to Formula 1 practice.