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We last looked at low-carbon cars a year ago (solartoday.org/transportation). Since then, a number of very efficient new cars have arrived in dealer showrooms. Last year, we observed that dealers in the United States offered no new cars rated at 40 miles per gallon. This summer, at least five 2009/2010 models, in showrooms now, carry Environmental Protection Agency ratings of 40 mpg or better in highway driving.

The cost of fuel has fallen more than 40 percent from its 2008 peak but has begun to rise again. Drivers in the United States have cut back their miles by about 1.6 percent from 2007 to 2008, and fuel sales fell by 4.7 percent because we parked our biggest gas hogs. In fact, U.S. gasoline sales peaked at about 66.8 million gallons per day in the summer of 2003, when regular-grade gas sold for $1.50 per gallon. By the summer of 2008, when regular peaked at more than $4 per gallon, gasoline sales, and consequent emissions, fell 18 percent.

With the drop in fuel price has come a drop in the popularity of efficient cars. At midsummer 2008, the average new Prius sat on a dealer’s lot for only 36 hours before being sold at a premium above its sticker price, and Toyota had begun building a Prius factory in Mississippi. By the spring of 2009, the Mississippi factory had been mothballed, and the average new Prius sat for 76 days on the dealer lot. The average price for a used Prius has dropped about 25 percent. One of our readers reported buying a 2006 model for just $15,000. In short, this may be the time to buy a small, efficient car. Prices will rise again with fuel prices.

And fuel prices will rise. In April, the national average pump price inched up at about 3 percent per week. Bill Reinert, national manager of advanced technology for Toyota, points out that the world has already passed “peak oil” outside of OPEC sources, so that a further increase in demand (due to growing markets in China, India, Brazil and Russia) will have to be supplied either by OPEC or by “unconventional” liquid fuels. “Beyond 2014, our ability to supply new liquid oil ends,” Reinert told an audience at the Conference on World Affairs April 6 in Boulder, Colo. Soon, cars will have to burn natural gas or biofuels — always constrained by the shrinking availability of water for irrigation and processing. Or they’ll run on electricity.

The motoring scene has changed dramatically, but some principles are unchanged from last year:

• The carbon generated in manufacturing any car usually exceeds the carbon emissions for the first year of driving. This means, over the short haul, operating an efficient used car puts less carbon into the atmosphere than buying and driving a new one.

• Cars burning biofuels, natural gas and diesel, along with hybrids and electric vehicles, can have dramatically lower carbon emissions than traditional gasoline cars. But the bottom line depends on where the energy originates.

• Most U.S. drivers want one car for commuting, local errands and highway driving.
Drivers with short-haul stop-and-go driving habits — big city delivery trucks and taxicabs, for instance — can make best use of the characteristics of an electric vehicle (EV) or a plug-in hybrid electric vehicle (PHEV) with a 40-mile range, also called a PHEV40. Drivers who do a lot of long-distance driving at highway cruising speeds will do best with a turbo-diesel. Most of us fall somewhere in between.

In the chart available for free download (download here), we’ve combined a lot of moving parts to estimate the carbon emissions of a variety of efficient cars.

Not surprisingly, the low-carbon champ will be any pure EV charging from a carbon-free source. If you have a photovoltaic (PV) array on your roof or a wind turbine in the back yard, or if you live in a state that gets all its power from hydroelectric sources, you can acquire a Tesla or some less glamorous EV, and only the driver and passengers will emit carbon dioxide. The next cleanest car on our list is a used Honda Insight two-seater, emitting 0.3 pound of CO2 per mile on gasoline or 0.06 pound if you run it on an 85 percent ethanol blend (E85).

If you have access to one of the new Toyota Prius plug-in hybrids, built by Toyota in limited quantities for fleet sales or remanufactured by a local conversion shop, you may cruise around town with zero emissions, or pump out 0.33 pound per mile in long-distance driving. A standard 2010 Prius emits 0.39 pound per mile in normal driving, and the new 2010 Honda Insight does about 0.48 pound per mile, beating out the light two-seater, pure gas Smart Fortwo (0.49 pound per mile). Close behind is the surprisingly efficient new Ford Fusion Hybrid.

Curb weight reflects the car’s general heft, in pounds. It’s what the car weighs with a full tank of gas but no passengers or luggage. EVs and PHEVs with nickel-metal hydride (NiMH) batteries are heavier than liquid-fuel cars or cars with expensive lithium-ion (Li-ion) batteries.

MPG is miles per gallon, according to tests conducted by the EPA. The EPA gives mileage for city driving, highway driving and combined; we’ve used the combined figure. Where that’s not available, we’ve averaged city and highway numbers. To convert MPG to kilometers per liter, multiply by 0.425.

Price is manufacturer’s suggested retail price in U.S. dollars (for new cars) and approximate retail market value for used cars.

Seats is number of seats, according to the manufacturer. If you carpool or plan to transport whole soccer teams, this is an important number. You might feel better about carbon emissions if you calculate pounds of CO2 per passenger-mile. We’ve done it for you, and the column labeled “12,000-mile carbon per seat” makes the relatively heavy seven-passenger Toyota Highlander SUV look pretty good. In fact it makes us wish for a nine-passenger van based on the same chassis. That might be the taxicab of the near future.

Drive categories include rear-wheel drive (RWD), front-wheel drive (FWD), full-time all-wheel drive (AWD) and on-demand four-wheel drive (4WD). 2/4WD means that the standard mode is RWD or FWD but that 4WD is an available option.

HP combined is the combined horsepower of the piston engine and any electric drive motor.

Drive type is the technology of the prime mover. IC indicates a normally aspirated (non-turbo) internal combustion engine using gasoline, compressed natural gas or ethanol fuel. Tdiesel is a diesel engine with a turbocharger, able to run on diesel or biodiesel. Hybrid uses an IC engine assisted by an electric motor. Hybrid(I) means a mild hybrid, in which the electric assist comes from an oversized starter motor and the IC engine always runs when the car is moving. PHEV is a plug-in hybrid, able to run an initial distance on battery power alone — for instance, a PHEV40 can run approximately 40 miles before the IC engine needs to charge the batteries. EV is a pure electric vehicle, and EV100 means it has the battery capacity to run approximately 100 miles on a charge.

Fuel types include gas, for cars that run on gasoline. Flex means the car is equipped to use either gasoline or an ethanol blend (but note that all modern gasoline cars can be cheaply modified to run on ethanol). D means diesel, and these cars can also run on biodiesel. CNG is compressed natural gas. Li represents lithium-ion batteries, and NiMH is nickel-metal hydride batteries.

12k mile CO2 direct is the approximate mass of carbon dioxide straight out the tailpipe in a typical 12,000-mile year of driving, given in pounds.

12k mile E-mode 100% coal applies to EVs and PHEVs. It estimates the pounds of carbon emitted in charging the vehicle for a 12,000-mile year of electric-powered driving if your electric utility uses coal-burning generation exclusively. Note that, if this is the case, your EV may produce a bigger carbon footprint than some modern high-efficiency hybrids.

12k mile E-mode 50% coal estimates the pounds of carbon emitted in charging an EV or PHEV for 12,000 miles of electric-powered driving if your electric utility uses coal-burning generation for half its delivered electric power. There is no column for carbon emissions where electricity is provided from carbon-free sources. In that situation, direct carbon emission is zero.

12k mile fuel cost is the approximate cost of fuel for driving 12,000 miles, assuming that electricity for charging an EV costs 11 cents per kilowatt-hour, gasoline and CNG costs $2 per gallon and diesel costs $2.15 per gallon. All these prices are bound to rise over time.

10-year cost is the cost per mile to operate the vehicle, combining purchase cost and fuel costs at 12,000 miles per year at today’s prices. This figure does not include taxes, insurance or maintenance costs.

12k CO2 lbs bio fuel approximates the pounds of CO2 emitted if a diesel vehicle operates on B100 (pure vegetable oil) or a gas/flex vehicle operates on E85 ethanol.

12k fuel cost bio fuel approximates the fuel cost to operate a diesel vehicle on B100, at $2.75 per gallon or a flex-fuel vehicle on E85, at $1.85 per gallon.

CO2 per mile bio approximates the pounds of CO2 emitted per mile when burning B100 or E85.

CO2 per mile fossil approximates the pounds of CO2 emitted per mile when burning petroleum fuel or charging from a coal-burning electricity source.

Cars are arranged on the chart in the order of their estimated direct tailpipe CO2 emissions. Naturally, the electric vehicles, with zero direct emissions, are at the top of the list. The “Generic EVs” are assumed to be four-passenger sedans. Assuming the battery pack weighs about 800 pounds, lithium batteries give roughly twice the range as nickel-metal hydride batteries. A number of mainstream automakers plan to introduce sedans in these categories over the next two to three years.

The Tesla Roadster has been in production for almost a year and has lived up to its performance claims. In March, the company unveiled the design for its Model S four-door sedan, billed as a seven-passenger family vehicle, with a range of 240 miles, at a target price of $60,000.

The original two-seat Honda Insight, discontinued in 2006, is still a great choice as a commuter car. It may become a collector’s item someday.

The Chevy Volt, scheduled for introduction late next year as a 2011 model, is a pure electric-drive vehicle with an auxiliary flex-fuel IC motor used for charging the batteries after about the first 40 miles. The term “series hybrid” describes this technology, in contrast to “parallel hybrid,” in which both the electric motor and the IC motor are linked directly to the transmission.

The Toyota Prius PHEV is available in limited quantities for sale to fleets — or you can upgrade the Prius you already have to this format for $10,000 to $20,000, depending on the batteries you choose to add. Note that Toyota warranties their original factory NiMH battery pack for 150,000 miles, and the warranty no longer applies if the car is modified.

The “Generic Theoretical PHEV van” would be a nine-passenger family van based on the Toyota Highlander drive train. It might look something like the Bright van on page 54.
Toyota’s new 2010 Prius is available in showrooms now, and the claimed 50 mpg performance is achievable in normal driving.

Ford’s new 2010 Fusion Hybrid, already in dealer showrooms, has been shown to get more than 41 mpg in highway driving. For now, it’s by far the most efficient car you can buy from an American factory and handily outperforms a number of much smaller cars.

Similarly, the 2009 Volkswagen Jetta TDI got 48 mpg in a highway driving test by a New York Times reporter. That’s Prius territory.

Finally, I included my own 13-year-old Subaru wagon. Driving carefully, I can milk 30 mpg from this beast, even with AWD and snow tires. It simply shows that a smallish engine and conservative design make for more efficient operation than you’ll get from any existing hybrid SUV.

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About the author: Seth Masia is managing editor of SOLAR TODAY. Contact him at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

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