MAY/JUNE 2008 |
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| Choosing a Low-Carbon Car |
While you wait for the zero-emissions car of the future, what’s the best car to drive now? The answer may surprise you. |
By Seth Masia
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General Motors claims that the Volt may be available for the 2010 model year. It’s going to be a plug-in hybrid, with a battery pack capable of going 40 miles before the 1-liter recharging engine fires up. Initially, that engine will be a three-cylinder flex-fuel (gasoline/ethanol) unit, but the car may later be available with a variety of engines, including diesel/biodiesels, fuel cells, or CNG models.
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Last September, a client flew me to Europe to look at some new products. We would visit four facilities in Germany, France and the Netherlands, in four days, crossing Liechtenstein twice. At the Düsseldorf airport he rented a sleek black Audi A4 station
wagon with a five-cylinder turbodiesel engine, and we wheeled onto the autobahn. According to the dashboard GPS, over the next four-and-a-half days my lead-footed client covered about 1,200 kilometers (750 miles) in 10 hours of driving, at speeds up to 200 kilometers an hour (124 miles per hour). I cowered in the shotgun seat. We flashed past huge elegant wind farms (Germany gets about 6.3 percent of its electric power from wind), but I kept one nervous eye on the speedometer.
We stopped for fuel once, and filled the tank again before returning the car to the rental agent. I calculated the damage: We had burned 71 liters (19 gallons) of diesel fuel. That’s 40 miles per gallon (17 kilometers per liter).
In North America, where diesel fuel is not yet clean enough to run in an engine like this, you can’t buy a new car that will get 40 mpg at 75 mph. You can buy a heavy Mercedes diesel sedan (but not in California and several Northeastern states). Audi, Volkswagen and BMW promise efficient diesels later this year.
Right now, however, you can buy a used Volkswagen Golf TDI or Jetta TDI that will get 45 mpg at 60 mph. And you can put biodiesel in the tank. In warm weather you could run it on vegetable oil.
Maximize your fuel mileage
The high-efficiency new cars look great, but consider that, from the standpoint of total lifetime environmental impact, the most conscientious choice may be to recycle an older car with a small, efficient engine — and then drive it for maximum efficiency. When you keep an older car on the road, you avoid all the extractive and emissive externalities involved in building a new one.
The first great expert on stretching fuel was Charles Lindbergh. On long overwater flights he ran his engines at the lowest practical rpm, and at the leanest possible carburetor setting. He taught these techniques to military pilots operating over the Pacific during World War II. He pointed out that the engine’s internal friction — a dead waste of fuel — rises with the square of engine speed. In your car, this means that at 2,800 rpm your car produces twice as much engine friction as it does at 2,000 rpm. The lesson: upshift early. Get the car into top gear as soon as possible. At 35 to 40 mph, cruise in fifth gear instead of fourth.
Accelerate smoothly and keep a steady foot on the accelerator. The cruise control is generally steadier than your foot, and can therefore save gas.
Keep the tires inflated, keep the engine tuned, keep the air filter and fuel filter clean. Minimize use of the air conditioner. Don’t idle when stuck in a long line of traffic — at the drive-through or while waiting for a train at a grade crossing, it’s kosher to shut the engine down. |
In North America, about a third of the greenhouse gases we produce come from burning transportation fuel. The United States burns more than 400 million gallons daily of gasoline and diesel fuel, putting 4 million tons of CO2 into the air. Daily, we import oil worth more than $1 billion. If we could replace all those fuels with domestic biofuel, we’d keep that money in the domestic economy, and drop transport CO2 emissions 83 percent to about 680,000 tons daily. It might cut our national greenhouse gas output, from all sources, by 28 percent.
It’s easy to argue with any of these numbers. I get most of my data from U.S. Department of Energy websites, which don’t count the externalized costs of energy. These costs include the energy balance for farming and processing of biofuels, the military cost of keeping oil flowing from Middle Eastern fields, and the energy cost of building the car and making its replacement parts, including tires, lubricating oil and batteries. Nor do these calculations account for efficiency losses. Remember that there are heat losses in chargers and inverters, so that to put 10 kilowatt-hours into a battery pack may cost 12 or more kilowatt-hours at the grid meter.
Steve Heckeroth, chair of the American Solar Energy Society’s Renewable Fuels and Sustainable Transportation Division, has done calculations including all manufacturing and fueling externalities. He concludes that a small car getting 30 mpg on gasoline puts 3.5 tons of CO2 out the tailpipe annually (roughly equal to the 7,825 pounds I calculate for 12,000 miles at 30 mpg). In addition, he figures on 4.5 tons of “upstream” externalities for that car, for a total of 8 tons. He also calculates that solar- and windcharged electric vehicle (EVs) cars are 60 to 3,000 times more efficient than bio-fueled engines. That makes zero-emission electric and plug-in hybrid cars a great deal more attractive.
Biofuels are controversial. Corn-based ethanol (America’s E85) offers at best a marginal positive energy balance, with pernicious economic effects especially on food prices. Sugar-based ethanol offers a better energy balance, but, like vegetable oil stocks for biodiesel, often creates incentives for the destructive clearing of tropical forests. Resolving these unintended consequences constitutes a major set of cultural, economic and geopolitical challenges.
Despite all these caveats, it’s clear that we can achieve environmental, financial and moral benefits by driving the most fuel-efficient cars and trucks.
We’re talking about several different technologies here, and each one works best on a particular duty cycle.
Electric vehicles (EVs), running purely on batteries, do well in short trips, and especially in stop-and-go driving. That’s because they draw little or no current while stopped, and their regenerative braking systems recover some energy during deceleration. Maximum torque occurs at zero engine speed, so the cars accelerate briskly from a standing start. Choose an EV for short commutes, running errands and making deliveries on city streets. The practical range limit for traditional lead-acid batteries is typically 20 to 30 miles (32 to 45 kilometers). Modern lithium-ion batteries may boost range to 40 or even 200 miles (65 to 320 kilometers).
Hybrid vehicles run on batteries in low-power situations, and use internal combustion (IC) power for accelerating, hill climbing and when the batteries have been drained. The IC motor shuts down when the vehicle comes to a stop. The duty cycle feels normal to the driver. A heavy hybrid has no efficiency advantage over a normal IC vehicle, and the hybrid loses its efficiency advantage when run long distances — that is, well beyond the range of the batteries.
A plug-in hybrid (PHEV) is a hybrid with an oversized battery pack that can be recharged from the grid while parked. Typically it can run up to about 40 miles on battery power alone.
Compressed natural gas (CNG) vehicles are common in fleet use, but the lightweight Honda Civic GX is also sold to the public. In some major metropolitan areas CNG fuel (methane) is available at filling stations. The range is limited because the reinforced high-pressure fuel tank carries the equivalent of only 8 gallons. The chief advantage is low greenhouse gas emissions: about 0.53 pounds per mile of CO2. In about 16 states you can buy or lease a home fueling station to compress gas from your utility line. Depending on local pricing, this may reduce fuel costs to about $2 per gallon-equivalent. The fueling station may cost $3,000 to $4,000, depending on local incentives.
Whatever happened to cheap, efficient cars?
By 1980, thanks to Middle Eastern wars, the price of oil had spiked to $65 a barrel. Millions of Americans discovered that peppy little Japanese cars could get 35 mpg. For instance, I bought a 4WD Toyota Tercel, a cute little station wagon with an “eager” 1.5-liter, 62-horsepower engine that got 40 mpg on the highway, at 67 mph. That year, about 25 percent of cars sold in the United States were Japanese imports, and Detroit laid off about a third of a workforce that had peaked,
in 1979, at 1.1 million.
In April 1981, under pressure from the American Big Three auto manufacturers and the United Auto Workers, the Reagan administration asked Japanese automakers to “voluntarily” restrict their exports to the United States. The Japanese, fearing action by Congress, agreed to limit U.S. sales to about 1.83 million cars per year. Quotas remained in place for the rest of the decade.
The Japanese factories quickly learned that they could continue to grow — not by selling more cars, but by selling more expensive, more profitable cars, and by building them here. Honda began upsizing the Accord, and laid plans for the 1986 introduction of the luxury-performance Acura brand. Toyota followed suit with the Lexus, and Nissan with the Infiniti, both for debut in 1989. The companies also began up-sizing their Light trucks to compete head on with Detroit.
At the same time, Saudi Arabia turned on the taps and sent the price of oil plummeting to $22 in 1986. Cheap and plentiful fuel gave Detroit a chance to resume selling gas guzzlers. The first SUVs reached the market in 1991. The era of the cheap, fuel-efficient imported car had ended. |
Turbodiesel IC vehicles milk as much energy as possible from diesel fuel, which contains more energy per gallon than gasoline. They do well in most duty cycle situations and can run without modification on any biodiesel blend. However, high bio-content oil fuels can solidify in low temperatures, so these engines often run on fossil diesel in wintry months and on vegetable oil in summer months.
Flex-fuel engines run on either straight gasoline or ethanol blends, but high-ethanol blends (typically 85 percent ethanol, or E85) contain about 80 percent of the energy of straight gasoline, and so offer fewer miles per gallon. For instance, the Environmental
Protection Agency says the Chrysler Sebring/Dodge Avenger gets 27 mpg (highway) on gasoline and 20 mpg (highway) on E85. Comparable figures for the Chevy Impala flex-fuel version are 29 mpg and 21 mpg. Most flex-fuel vehicles sold in the United States
are sizeable pickup trucks and vans, and not notable for fuel efficiency (they’re exempt from the 27.5-mpg federal mileage standard because they can’t comply, especially when running on alcohol). Any gasoline-burning car sold in the United States since 1995 can, in theory, be modified to run on E85, usually by replacing the oxygen sensor. This applies to hybrid and PHEV cars, too.
There’s no such thing as an automobile engine that will run on both biodiesel and ethanol. In theory, an external combustion or Rankine cycle engine could burn any liquid fuel, or even wood pellets. That puts us into Stirling engine and even steam power territory. And no manufacturer has yet introduced a hybrid or PHEV with a biodiesel IC motor. General Motors has shown prototypes of a diesel-electric hybrid, based on the Chevy Volt platform and carrying the Opel and Saturn brands for Europe and North America. Volkswagen has announced plans for a 69-mpg diesel hybrid.
Finally, large auto manufacturers occasionally offer small runs of very efficient vehicles available only in limited markets. For instance, the California Air Resources Board mandates a category of cars called partial zero emissions vehicles (PZEV), and a few
thousand hybrid cars with long-life emission systems meeting the standard have been sold in local markets on the West Coast and in the Northeast.
Click here to download a chart of representative “efficient” vehicles, available now or promised by their manufacturers within the coming year. Included are a few discontinued high mileage small cars, cheaply available on the used market. Because the cars run on a variety of fuels, alone and in combination — gasoline, ethanol, diesel, biodiesel and electricity — direct comparison is a complex matter. In fact, comparing vehicles is very much a matter of priorities. Do you define efficiency in terms of lowest operating cost or lowest carbon emissions? In calculating operating cost, do you discount the initial cost over the operating life of the vehicle, and how do you determine that lifespan? Do you accept standard tax-code depreciation rates? How do you value externalities for vehicle manufacturing and fuel production? And do you calculate emissions and costs by the mile or by the seat/mile?
We can’t answer all those questions in a short magazine article, so the chart should be read as a rough guide, not an engineer’s or economist’s solution. Feel free to download the spreadsheet and put in your own local prices, or change the underlying assumptions, or put in additional vehicles. The chart is founded on these assumptions:
• Gasoline burned in a piston engine produces about 19.56 pounds of CO2 per gallon (2.34 kilograms per liter).
• Diesel fuel produces about 22.38 lb. CO2/gal. (2.68 kg/l).
• Biofuels (both vegetable oil and ethanol) produce about 3.3 lb. CO2/gal. (0.39 kg/l).
• Ethanol has roughly 80 percent of the energy content of gasoline.
• Coal burned in a modern power plant produces about 1.37 pounds of CO2 per kilowatt-hour (0.62 kg/kWh).
• The average four-wheeled electric vehicle gets about 4 miles (6.5 kilometers) per kilowatt-hour. Electric scooters often get 10 miles (16 kilometers) per kilowatt-hour, but have smaller battery packs so the practical range limit is still 30 to 40 miles (48 to 65 km).
• Across the United States, electric power from the grid costs an average of 11 cents per kilowatt-hour. In Colorado, I pay about 9 cents, so it would cost me over twice as much to charge up my EV if I were living in Hawaii and paying 23 cents.
• Finally, we assume that most SOLAR TODAY readers are typical real-world motorists who will use one car for commuting, around-town errands and frequent highway driving. Some of us live in snow country and need to pay a modest weight penalty
for all-wheel drive.
Lowest-carbon footprint using biofuel (E85 or B100):
1. Any electric vehicle running on a noncarbon source (photovoltaic, wind, nuclear): 0 lb. of CO2 per mile (lb. CO2/mile)
2. Any plug-in hybrid (Prius PHEV, Volt PHEV) run in electric mode only
3. Honda Insight, bought used: 0.06 lb. CO2/mile
4. VW TDI (or similar): 0.07 lb. CO2/mile
5. Toyota Prius, Honda Civic hybrid, or PHEV run in hybrid mode: 0.09 lb. CO2/mile
6. Typical old motorcycle or small car at 42 miles per gallon: 0.09 lb. CO2/mile
7. Mercedes Smart Car: 0.1 lb. CO2/mile
8. Nissan Altima Hybrid/Toyota Camry Hybrid (identical drive trains): 0.12 lb. CO2/mile
9. Any small car getting 30 miles per gallon: 0.13 lb. CO2/mile
10. Honda Accord Hybrid (used): 0.15 lb. CO2/mile
11. Chevy Malibu Hybrid/Saturn Aura Green Line (identical drive trains): 0.15 lb. CO2/mile
12. Lexus GS450h: 0.17 lb. CO2/mile
13. Ford Escape Hybrid/Toyota Highlander Hybrid SUVs: 0.17 lb. CO2/mile
14. Lexus LS600HL: 0.19 lb. CO2/mile
Lowest-carbon footprint using fossil fuel (gasoline, diesel, natural gas or coal-fired electricity):
1. Honda Insight, bought used: .3 lb.CO2/mile
2. Electric vehicle or PHEV run in electric mode only: .34 lb.CO2/mile
3. Toyota Prius: .43 lb.CO2/mile
4. Honda Civic Hybrid or PHEV run in hybrid mode: .47 lb.CO2/mile
5. Typical old motorcycle or small car (42 mpg): .47 lb.CO2/mile
6. Mercedes Smart Car: .49 lb.CO2/mile
7. VW TDI (or similar): .5 lb.CO2/mile
8. Honda Civic GX: .53 lb.CO2/mile
9. Nissan Altima/Toyota Camry Hybrid: .59 lb. CO2/mile
10. Any small car getting 30mpg: .65 lb. CO2/mile
11. Chevy Malibu/Saturn Aura Hybrid: .72 lb.CO2/mile
12. Honda Accord Hybrid: .75 lb.CO2/mile
13. Lexus GS450h: .82 lb.CO2/mile
14. Ford Escape/Toyota Highlander Hybrid SUVs: .85 lb.CO2/mile
15. Lexus LS600HL: .93 lb.CO2/mile
2008 Model Year Overall Gasoline Economy Leaders
(according to the U.S. Environmental Protection Agency)
| Rank |
Model |
City/Highway MPG |
| 1 |
Toyota Prius |
48/45 |
| 2 |
Honda Civic Hybrid |
40/45 |
| 3 |
Nissan Altima Hybrid |
35/33 |
| 4 |
Ford Escape Hybrid FWD |
34/30 |
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Mazda Tribute Hybrid 2WD |
|
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Mercury Mariner Hybrid FWD |
|
| 5 |
Toyota Camry Hybrid |
33/34 |
| 6 |
Toyota Yaris (manual) |
29/36 |
| 7 |
Toyota Yaris (automatic) |
29/35 |
| 8 |
Ford Escape Hybrid 4WD |
29/27 |
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Mercury Mariner Hybrid 4WD |
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Mazda Tribute Hybrid 4WD |
|
| 9 |
Toyota Corolla (manual) |
28/37 |
| 10 |
Honda Fit (manual) |
28/34 |
The Answer
If I need to get the kid to school and myself to the office, this week, I’ll pick the most efficient vehicle available right now. If I had a Golf TDI, I’d put recycled vegetable oil in it. But I don’t. Instead, I have an old Subaru. That’s what I’ll continue to drive, because buying a new car incurs the “upstream” CO2 externalities that Steve Heckeroth calculates exceed the actual tailpipe emissions. I’ll buy a diesel PHEV as soon as I can get a cheap one. I’ll fuel it with vegetable oil and charge it from my grid-tied PV array. I promise.
About the author: Seth Masia is managing editor of SOLAR TODAY. He gets 30 mpg in a 1996 Subaru, 42 mpg on a 1974 Moto-Guzzi, and 10 miles per bagel on a 1986 Rossin road bike. For latest auto data, go to solartoday.org/transportation.
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