The 2012 Fisker Karma (read our drive here) has finally been EPA certified, which means that Fisker Automotive can begin selling the car to customers. This is great news for the fledgling automaker, but the low fuel-economy numbers of the extended-range electric luxury sedan are being lambasted for being so disappointing. Instead of simply presenting the EPA’s figures and making snarky comparisons between them and the better numbers promised by Fisker when the Karma debuted at the 2009 Detroit auto show, we dug a bit deeper. We studied the Karma’s mechanical specifications to better explain the efficiency gap between it, Fisker’s original claims, and one natural competitor, the conceptually similar Chevrolet Volt.
So how “bad” is the Karma’s rating? The EPA’s testing revealed the sedan could travel just 32 miles on electricity alone. During those 32 miles, expect to achieve 52 MPGe combined; both numbers fall short of the Chevrolet Volt’s electric-only range of 35 miles and 94 MPGe. Things go from bad to worse once the Fisker’s 260-hp, turbocharged 2.0-liter four fires up to extend the car’s range. It swills high-test to the tune of 20 mpg combined, barely besting a V-6–powered Ford F-150. The EPA’s numbers are much lower than Fisker Automotive’s early claims of 50 miles of electric-only range and average fuel economy of 100 mpg.
Weight is a big factor for the lower numbers. According to Fisker Automotive, the Karma weighs 5300 pounds (the Volt is a relatively svelte 3755). That’s a lot of car to move around—the 2012 Porsche Panamera S hybrid is nearly identical to the Karma in size, price, and performance, but weighs 900 pounds less (and gets 25 mpg combined, but can only travel short distances under electric power alone). Excess pork helps explain why the Karma’s electric range is less than the Volt’s, despite the Fisker’s higher-capacity 20-kWh battery pack.
Weight not only hurts the Karma when running in electric-only mode, but in combination with the Karma’s hybrid system layout—yes, the Karma is technically a hybrid—it also decimates the car’s efficiency when the gas engine kicks in. With the gas engine running, the car operates as a series hybrid. This means that the engine powers a generator, which powers the electric motors that rotate the drive wheels—so the power in the system flows in a series. Conversely, the Volt can operate as a series hybrid, a parallel hybrid, or both at the same time. As such, the Chevy cannot claim full EV status, but the efficiencies of the various components of the drive system are all optimized. For a deep dive on how this works, check out our explanation here.
Series hybrids can be efficient, but the system still has several inefficiencies because there are energy conversion losses at each “step” in the series. First, the engine must convert gasoline into torque (internal combustion engines are about 40-percent efficient). After that, the generator converts that torque to electricity, netting another efficiency loss. Finally, electricity is reconverted to torque in the car’s two electric motors, scoring yet another loss. In a typical gas- or diesel-powered automobile, there is a single conversion loss when fuel is converted to torque. (Check out our recent comparison test between the Chevrolet Volt and the Cruze Eco to see how “old-school” tech can be coaxed to produce high-tech-beating fuel efficiency.) Even without the efficiency losses associated with series operation, the Karma’s gas-powered engine isn’t terribly efficient on its own—we saw just 23 mpg behind the wheel of a 3080-pound Pontiac Solstice GXP coupe powered by the same engine.
Of course, the Karma’s lower-than-expected fuel economy may not matter much to potential customers who intend to use it as a stylish and luxurious green machine. Fisker Automotive, for its part, doesn’t seem particularly concerned with the EPA’s ratings. The company is positioning the Karma primarily as an EV; that it can serve as a rapid sports sedan that can keep rolling even when the batteries die seems almost secondary. We agree with this marketing approach—the Karma is worlds quicker, more luxurious, and more visually stunning than a Chevrolet Volt, but can still play the part of silent, near-zero-emissions EV almost as well. Even pretending the $96,895 Karma is a typical, large V-8–powered sports sedan—and Fisker claims it can hit 60 mph in 5.9 seconds—20 mpg combined ain’t bad. Plus, what else can you buy for $100,000, electric or not, that has anything close to the exclusivity or the curb wattage of the Karma—along with a side helping of green?
No comments:
Post a Comment
Thank's!