October 29, 2011

LifeCycle Energy Analysis for YOUR car

Time to step away from the "vanilla" car and estimate the total energy used to manufacture and drive a particular car over its lifetime.

The GREET model developed at Argonne National Lab considers how much energy it takes to manufacture the "average" car. We take a bold step and make the assumption that the manufacturing energy increases linearly with the weight of the car, so if my car weighs 30% more than your car, it took 30% more energy to manufacture my car than yours.

This is not an exact calculation, but will serve for a rough estimate. From the GREET model results, the energy to build a car (the "vehicle cycle") is about 30MJ per pound for a conventional car with an internal combustion engine, and about 39MJ per pound for a hybrid vehicle.

The other numbers we need to keep in mind is that there is 121MJ in a gallon of gasoline, and 138MJ in a gallon of diesel.

We're ready to do a rough comparison. The table below shows a few cars with their kerb weight, the energy to manufacture them, the real-life fuel economy, the total fuel energy for 150,000 miles, including the well-to-pump energy ("fuel cycle"), and finally, in the right-most column, the total energy consumed in making the car and driving it for all those 150,000 miles (but excluding any repairs).


Lifecycle Energy Analysis
(assuming total 150,000 miles)

Real Fuel
Toyota Prius
Toyota iQ
VW Golf TDI 1.6L
VW Golf TDI 2.0L
Honda Fit
Honda Odyssey
Audi A4 Avant 2.0 TFSI
Audi A4 Avant 2.0 TDI

For total lifecycle energy, Toyota Prius, the only hybrid model in the table, does exceedingly well, better even than tiny Toyota iQ which in Japan falls in the "2Box" category, that is, a box on wheels that fits two people. Two very good friends.

The VW Golf with the 1.6L diesel engine does only a little worse than the Prius, the one with the 2.0L engine quite a bit worse. Here is a clear example of CelloMom's idea that, carbon and dollar wise, you can have your cake and eat it too: the 1.6L Golf will be cheaper to buy, cheaper to drive, and give you the feelgood factor of significantly lower carbon emissions.

The smaller Honda Fit has nearly the same total lifecycle energy as the Golf with the larger engine; but it is significantly cheaper to buy, as well.

At 1232GJ total lifecycle energy, the Odyssey minivan consumes 2.5 times more energy than the Prius, which is not so great considering you can transport only 1.4 times as many people in the minivan. Energetically speaking the minivan is more attractive only if you have five or more passengers to move every day, e.g. if you share the school commute with friends.

The Audi A4 station wagon makes sense only for the most frugal engine: for the less frugal ones you might as well buy a minivan and get more cargo space and passenger flexiblity, foregoing the carbon feelgood factor. Here the cost equation is less clear, since the diesel version has a higher purchase price. But at a fuel economy of 39mpg for the diesel, as compared to 24mpg for the gasoline version, the frugal diesel is still cheaper overall.

October 21, 2011

What is greener: drive your old gas guzzler it till it dies, or trade it for a new gas sipper?

CelloMom goes digging into the lifecycle analysis for automobiles, and makes some astonishing discoveries.
From the green perspective: trade it in!
From the greenback perspective: keep it till it falls apart.

Those of us who worry about carbon emissions from our tailpipes, often wonder whether it would make sense to buy a new car with better fuel efficiency. After all, that new car takes energy and raw materials to build, and carbon dioxide is emitted during its sourcing and manufacture.

This is where it makes sense to do a lifecycle energy analysis, in which one considers the total energy required to produce something, in this case passenger cars, and to run it during its lifetime. There is a nice summary in a Google Answers thread, which contains many citations. MIT's Lab for Energy and the Environment (LFEE) published a report called "On the Road in 2035: Reducing Transportations' Petroleum Consumption and GHG Emissions" which contains lifecycle analyses of various types of cars; GHG stands for greenhouse gases.

In this post, CelloMom uses the numbers from the recently updated and extremely thorough research done at Argonne National Lab, culminating in a model for Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation, or GREET for short. This team has considered everything, from the obvious emissions from burning the gasoline (including the well-to-pump energy cost), to the energy cost of mining and refining the lead for the car's battery, to the brake fluid and the plastic insulation around the electrical wires. Everything.

You can download the full-blown GREET model and play with it on an Excel spreadsheet. CelloMom, who gets agitated in all the wrong ways by Excel, was content to read the report on how the model was built (e.g. what assumptions went into it), which highlights some of the salient conclusions.

CelloMom is still reeling a bit from some surprises encountered in this report.


The GREET report considers the "vanilla" car weighing 3330 lbs, and reaching a total lifetime mileage of 160,000 miles. At 24.8 mpg, that requires 6452 gallons of gasoline at the pump.

Surprise: It takes about the same amount of energy to produce a hybrid vehicle and a conventional gasoline car with an internal combustion engine:

This Vehicle-cycle Energy is about 100 million BTU = 100 GJ (GigaJoules) for a car weighing 3330 lbs (use CelloMom's cheatsheet on the units for energy). The carbon emissions is about 8500 kg CO2 / car.

For gasoline engines, the energy burnt during the car's lifetime is 121 MJ/gal times the total number of gallons of gas consumed. So:
Operation Energy = 121 MJ/gal * 160,000 mi / 24.8mpg = 781 GJ
Operational CO2 = 8.80 kgCO2/gal * 160,000 mi / 24.8mpg = 56,800 kg CO2

The fuel cycle accounts for the well-to-pump process of getting the oil out of the ground, refining it and transporting it to the gas station:
Fuel-cycle energy = 781 GJ * 17 / 83 = 160 GJ
Fuel-cycle carbon = 11,630 kg CO2.

BIG surprise: The vanilla car consumes a total of 1041 GJ of energy, of which its production accounts for only 100GJ, or less than 10%. The story for carbon dioxide emissions follow the same lines.


WHOA! CelloMom has always had the impression that making the car takes a lot more energy than driving it, but is hereby definitively shown to be WRONG. From under her dunce cap, CelloMom will now humbly mumble that it always pays to do the math.

So there you are: from a purely green perspective, and considering only the energy and the carbon footprint issue, yes, go ahead, trade in your gas guzzler for a gas sipper.

Obviously, it makes no carbon sense to do this every year, but consider this: While many Americans trade in their car after 4-5 years (about the lifetime of the car loan), the average life span of a car is about 13 years. That means that all those cars that are traded in go on to find second, possibly third, owners, who have presumably traded up from even older cars. Since cars tend to become less efficient as they get very old, your purchase of a new gas sipper contributes to raising the average fuel efficiency of the national fleet.

Before your green-leaning heart starts beating too loudly, it is interrupted by the voice of the greenback. For the purchase of a new car is expensive. Our "vanilla" car had a fuel economy of 24.8 mpg. Suppose you buy a gas sipper that does 50mpg; suppose its total price, after subtracting any trade-in, is $20,000. At today's gas prices of $3.50 / gallon you would have to drive 282,000 miles (= $20,000 / $3.50 per gal / (1/24.8mpg - 1/50mpg) ) to break even.

It tells you that gas is cheap. At $10/gal, the break-even point would be around 100,000 miles; and at $20/gal, it would be 50,000 miles. Even the Europeans aren't there yet.

Final conclusion:
IF you're ready to say goodbye to the car you currently own anyway, by all means downsize (or at least downsize the engine) to a gas sipper and reap the benefits of lower costs for the new car AND collect the feelgood factor for increasing your personal fuel efficiency as well as the national one.
BUT IF you could happily keep on driving your current conveyance, upgrading to a new gas sipper would earn you serious greenie points, but only that; don't do it for the savings, unless your current car has very high trade-in value. There are several calculators, including Edmund's, that help you make the call - but in general you will be disappointed, dollar-wise.

October 20, 2011

Review: Honda Accord

The Honda Accord has grown larger and wider, perhaps following the lead of the people who were young at its introduction. In the US, it was in the "compact car" category in 1976; now it is classified as a "full size" car. But it hasn't grown equally in all parts of the world.

When CelloMom was in college, her then-boyfriend Juan got his first job, and his first new car, a metallic-blue Honda Accord hatchback. Juan drove it happily through the commuter traffic, and less happily on shopping trips when CelloMom begged him to. We still call each other now and then, and compare notes on parenthood with our respective children, foreign languages, and a host of other things. When CelloMom mentioned this blog, Juan told her that he still drives a Honda Accord, albeit a different one from that first hatchback. Suddenly CelloMom realised that she hasn't seen an Accord hatchback for a while, and decided to look into it.

This baby sure has come a long way. At its introduction (1976) the Accord was just 4.115m long, and was offered only as a 3-door hatchback. Its 1.6L engine put out 68 HP, enough to give a nimble feel to its 2000-lb weight. It was well-known for its excellent fuel efficiency, 46mpg hwy.

Fast-forward to 2012. The 4-door sedan (US version) is now 4.94m long, or nearly three feet longer than the original hatchback. The current 2.4L engine gets a spec of 23 / 34 mpg (cty/hwy). The V6, 3.5L monster gets just 20 / 30 mpg (cty/hwy); it puts out 271HP to push around its 3600 lbs.

What happened here? As the drivers got older (and larger), they were sold increasingly bloated versions of the same car, which need larger and larger engines to keep that feeling of nimbleness? But wait: as drivers get older and hopefully a little wiser, would they not have less of a need to zip around the highways? So why would one need 271HP in a passenger car that's allowed to go at most 65mph in most states?


Honda Accord, versions offered in selected countries

*larger version (called Honda Inspire in Japan)

2.2L Diesel
4-cyl, 16vlv

4-cyl, 16vlv

4-cyl, 16vlv
V6, 24vlv
24 mpg
It doesn't have to be that way. In fact, in Japan, the Accord comes with a choice of a 2.0L and a 2.4L engine, and it is only 4.73m long. That's nearly 8 inches shorter than its US counterpart, but still about two feet longer than the 1976 hatchback. The larger US-sized model is available in Japan as the Honda Inspire, and comes only with the 3.5L V6 engine. CelloMom is not sure to what one is supposed to feel inspired.

In the UK, and elsewhere in Europe, the smaller Accord comes not only with a 2.0L and a 2.4L gasoline engine, but also with a 2.2L diesel option, with a 41mpg real-life efficiency. For fuel economy, this engine is the best you can do in today's Honda Accord.

In the Netherlands, you can buy the 2.4L engine only for the "Executive" trim level, which starts at € 42,490 (about $ 58,400 at October 2011 exchange rates). Falling in the "D" category for carbon emissions, a pretty hefty carbon surcharge is included in the MSRP. You don't have to even try selling the Dutch the 3.5L V6 engine: it would get taxed too punitively, both at purchase and in the annual road tax which will soon depend on the car's carbon emissions.

The oddest choice is given to would-be Accord buyers in Brazil: only the larger US model is available there, but with the largest and the smallest gasoline engines; no middle way. No diesel option, either. (What's that about?)

There is no doubt that there is plenty of room for a cello in either version of the current Accord, even in the US version which, bafflingly, has a smaller trunk volume than the Japanese/European version, despite being longer overall. But this car has way outgrown CelloMom, who would probably look like a little old lady trying to peek over the steering wheel.

As for Juan, CelloMom has caught a glimpse of him on a YouTube clip. He has a few more gray hairs - and he looks as trim as ever. CelloMom would bet he regularly tells Father Time to eat his dust on his daily run. When he is ready to say goodbye to his current trusty Accord, will he really be ready to drive around in a full-sized family sedan? One of which the fuel expense eats into the savings for future college tuition?


Honda Accord, Same-Model comparison, different engine.

US (JP Inspire) Japan, Europe, UK
Type Accord Sedan LX Accord Saloon ES
Year 2012 2012
Emissions rating ULEV-2/PZEV EURO5 "B"
MSRP $ 21,380 £ 23,325 (US$ 36,900)
CelloMom Rating 3 4
Fuel Economy:
City/Hwy quoted 23 / 34 mpg 39 / 61 mpg_imp
(32 / 51 mpg_US)
Avg. quoted 27 mpg 50 mpg_imp
(42 mpg_US)
Avg. actual   49.4 mpg_imp
(41 mpg_US)

2.4L 4-cyl 16-valve

2.2L 4-cyl 16-valve
Power 177hp @ 6500rpm 148 HP
Gears 5-spd manual 5-spd manual
Fuel Reg. unleaded Diesel
Length, mm(in) 4935mm (194.5in) 4726mm (186in)
Width, mm(in) 1845mm (72.7in) 1840mm (72in)
Height, mm(in) 1486mm (58.1in) 1440mm (57in)
Weight, kg(lbs) 1487kg (3279lbs) 1540kg (3395lbs)
Trunk volume, liters(cuft) 420L (14.7cuft) 467L (16.4cuft)
Turning radius, m(ft) 11.3m (37.7ft) 11.0m (36.8ft)
Top speed, kph(mph)   212 kph (132mph)

October 15, 2011

Is it ultimately cheaper to own an electric car?

Last week, CelloMom pondered the carbon issue around electric cars. Now it's time to look at the cost issue. The Nissan Leaf costs less than 3 cents/mile to drive, compared to 7¢/mile for the Toyota Prius. But the Leaf has a much higher sticker price.

The table below compares the same cars that were highlighted in the post on carbon-equivalent MPG-c, in terms of fuel efficiency, cost to drive 100 miles, and purchase price. The carbon emissions are thrown in once more just to keep the numbers handy.

The real-life fuel economy is copied from the tables on the MPG-c post, as is the CO2 emission. As usual, MSRP is the "from" price without the bells and whistles offered separately by the automakers. The MSRP for the Nissan Leaf does not include the $7500 tax break currently offered; CelloMom is not optimistic that this tax break will be around for long: We can't afford it, unless it is offset by an aggressive gas guzzler tax.

For the per-mile cost to drive the electric Nissan Leaf, CelloMom used the average price of electricity in the US in September 2011, which was $0.11/kWh. The range is $0.08-$0.18, depending on where you live. For the other cars, the average fuel price at the pump used is $3.51/gallon gasoline and $3.79/gallon diesel.


Fuel Economy, Carbon Emission, Cost; all averages.

Make/model Real-life
Fuel Economy

Cost /

Nissan Leaf 25 kWh/100mi 0.338 $ 2.75 $35,200
Toyota Prius 50 mpg 0.47 $ 7.02 $23,520
Honda Fit 35 mpg 0.67 $10.03 $15,100
Honda Jazz 40 mpg 0.58 $ 8.78 €10,820
VW Polo diesel 57 mpg 0.47 $ 6.64 €10,800
VW Golf (2001) 20 mpg 1.17 $17.55 $17,800


Suppose that you keep your next car for 12 years, and drive it 100,000 miles. For simplicity, just to get our head around the numbers, suppose for a moment that you can forego financing, so the purchase cost of the car is pretty much the MSRP plus the local sales tax. In the following, we are going to ignore the cost of insurance, which you need to have for any car, and the cost of repairs, which is completely unpredictable. We even ignore the possibility of having to replace the battery in the electric car before the 100,000 miles are up. We consider only the purchase price and the per-mile operating cost.

Buying a Nissan Leaf and driving it 100,000 miles would cost $35,200 for the purchase, plus $2750 for the fuel, or $37,950 together.
The corresponding cost for the Honda Fit would be $24,180 (that's $15,100 for the purchase and $9080 for 2857 gallons of gas). So the Honda Fit is cheaper to own, at today's gas prices around $3.50/gal.

But now let's turn it around, and ask: at what gas price does it make more sense to buy a Leaf? Assuming the cost of electricity stays the same, the cost to buy and drive the Nissan would remain $37,950. Subtract the MSRP for the Fit to get your fuel budget: $37,950 - $15,100 = $22,850. Since you need 2857 gallons to drive the Fit for 100,000 miles, a gas price of $22,850 / 2857 gallons = $8.00/gal would get you to the break-even point, where owning the Fit would cost as much as owning the Leaf with its much higher purchase price but much lower per-mile cost. Above $8.00/gal, it would make more dollar sense to buy the Leaf.

For the more frugal VW Polo (assume purchase price of $16,000) the break-even point would be at around $12/gallon diesel. Don't laugh, and don't cry. $10/gal is what Europeans are paying now for their gasoline, and if you believe the Peak Oil numbers, $15/gal is not outside the realm of possibilities, even for the US.

For your own purposes, adjust the purchase price as appropriate. For instance, subtracting $7500 for the electric-vehicle tax break shifts the Fit/Leaf breakeven point to a gas price of $5.37/gal (this is a serious incentive!). Add your state tax, if any. Add any financing expenses. Adjust the fuel costs to reflect your particular situation. And make a guess (and this is anyone's guess) as to the price of both gasoline and electricity for the next 10 years or so.

CelloMom's 2001 VW Golf has so far been reasonably trusty; but quite apart from its oversized carbon footprint, it costs 18 cents a mile to make it move, more than twice the per-mile cost of a Prius and more than 6 times as much as that of a Leaf. From a cost consideration, we will have to say goodbye to it if the price of gas keeps rising. But then there's the carbon footprint of manufacturing a new vehicle. CelloMom will have to look into that next.

October 12, 2011

Review: Mazda 2 / Mazda Demio

A brave little engine with a exceptionally high compression ratio packs a punch in this very cute and very frugal gas sipper.

CelloMom's friend Kumiko spent a few weeks in Japan this summer so CelloMom asked her what car was surrounded by the biggest buzz in Japan. The answer came back almost instantaneously: the Mazda Demio. There must have been quite a media campaign surrounding the launch in June 2011 of the Demio with SkyActiv engine.

In the US this car is known as the Mazda2; it has the same platform as the Ford Fiesta. You can vary the trim levels on the Mazda2: Sport and Touring, but both come with a 1.5L DOHC engine with an actual combined cty/hwy mileage of 35 mpg for the 5-speed manual version. The official mileage for this engine is 17.8km/L (42mpg) according to the Japanese JC08 standard. (The auto transmission gets 33mpg average in real life).

Japanese buyers of this car are mostly young single women, if you go by the photos on the Demio site. The Demio owner is an independent type, who enjoys trekking along the highways and byways on her weekend off. One suitcase and a beauty case fit in the back. Or her shopping bags and such. Not a sign of a baby carriage on this website. Her cello (if any) would have to go on the back seat. Or she could fold down those back seats (in a 40-60 configuration) - but they don't go down flat, this is not a cargo hauler.

If this young person lives among the tea plantations on the flanks of Mount Fuji, she might need oomph under the hood. But if she stays mostly in the flat-terrain Tokyo-Osaka corridor she won't need the 1.5L, or even the 1.35L engine; instead, she might opt for the new 1.30L engine with the SkyActiv-G designation.

What's special about this engine is that is has an unusually high compression ratio: inside an engine's cylinder, during one firing cycle the piston moves from the maximum-volume position at the end of the cylinder, to the minimum-volume position at the head of the cylinder, where the fuel is ignited and drives the piston out again. In many car engines, the maximum volume is larger than the minimum volume by a factor, called the compression ratio, close to 10; in the SkyActiv engine that compression ratio is nearly 15. CelloMom figures this gets the fuel/oxygen mix closer to the optimal point, similar to turbocharging, and results in better fuel economy.

The official fuel economy is 25 km/L (59mpg); CelloMom estimates that the actual real-life mileage is around 45mpg. That is not bad, considering this is not a diesel engine, and doesn't need a turbocharger. Note the persistently blue theme for the Demio site: blue is the new green!

For CelloMom, who is neither young nor independent, the Demio or Mazda2 is a bit too small. CelloMom needs to move a family, plus a cello. Pity. Perhaps later, when it's just CelloMom and CelloDad, and no cello, this will work out.


Mazda2 / Mazda Demio.

Mazda2 (US) Mazda Demio (JP)
Type 1.5 Sport 1.3 SkyActiv-G
Year 2011 2011
Emissions rating ULEV2
MRSP US $14,180 ¥ 114,9000 ($15,000)
Fuel Efficiency:  
City/Hwy quoted 29/35
avg. quoted 25km/ L (59mpg) (JC08)
avg actual, l/100km(mpg) 35mpg (DOE) est. 45 mpg
CO2 quoted, g/km 135 93
Engine 1.5L DOCH 4cyl 1.3L DOCH DISI
Power 100HP @ 6000rpm 84HP @5400rpm
Gears 5-spd manual Auto CVT
Fuel Unleaded
Length, mm(in) (156in) 3.96m 3.900m
Width, mm(in) (69in) 1.75m 1.695m
Height, mm(in) (58in) 1.47m 1.475m
Weight, kg(lbs) (2306 lbs) 1046 kg 1010kg
Trunk volume, liters(cuft) (13 / 28 cuft)
Turning radius, m(ft) (32ft)
Top speed, kph(mph)

October 7, 2011

The charged issue of electric cars

Are electric cars better for the environment? CelloMom has her own take on "MPG equivalent" and "CO2 emissions" that look so glowing on EPA stickers for electric vehicles.

Electric vehicles are now often touted as the way to help automakers meet the new CAFE standards for fuel economy. A few electric cars are already for sale, and their manufacturers like to stress the "zero emissions" aspect. CelloMom made a few eye-opening discoveries while comparing them to other cars in terms of fuel efficiency and carbon emissions.

This all started when CelloMom spotted the EPA sticker for the Nissan Leaf that says "0" in the carbon emissions box (lower right-hand corner). The same EPA sticker also says that the Leaf has an "mpg equivalent" of 99mpg. That all sounds impressive. Impressive enough to make CelloMom want to check the numbers for herself. And this is what she thinks it ought to look like:

About those emissions.
Of course you can't deny that an electric car has zero tailpipe emissions. But saying that is like saying that you have no personal household garbage - because you eat out all the time. In reality, you are contributing to the garbage pile at the various restaurants that you patronise. So let's ask how much total energy it really takes (and how much CO2 is generated in the process) to get the charge into the battery that gives you 34kWh/100mi as it says on Nissan Leaf's sticker, or the slightly better 25kWh/100mi that most owners say they actually get.

CelloMom is not the first to point out that about two-thirds of the US electricity supply feeding those electric cars comes from burning fossil fuels (45% coal, 23% natural gas). The losses are staggering: only 33% of the energy inherent in the coal or natural gas fed into the power plant actually comes out as electricity.

If you ask how much total carbon dioxide (CO2) is released in the entire process of getting the kiloWatt-hours (kWh) of energy into the car's battery, you find that for the Nissan Leaf it is about 153g/mi (0.338 lbs/mi) for the average US owner getting their power from the local utility. This is really not bad; it's just not overwhelmingly great. It's just a bit (20-25%) better than the best small-engined cars that you can buy in Europe now.

Back to MPG.
The EPA calculates the equivalent mpg, or MPG-e, by comparing the energy stored in the battery to the energy you would get by burning a gallon of gasoline, and dividing it by the distance (in miles) you can drive the car on that battery charge. CelloMom argues that the more reasonable measure would be to compare the total carbon emissions, 153g/mi, to the carbon emissions from burning a gallon of gasoline. According to that measure, the fuel efficiency which CelloMom calls the carbon-equivalent mpg, or MPG-c, would be 57mpg. It's pretty good -- but not as impressive as the 99MPG-e on the sticker would suggest.

CelloMom emphasizes: these numbers are average for the US as a whole. Your particular utility's profile might be different: in Oregon there is a lot of hydropower in the mix. In other states it's more than half nuclear. This means that in some other states the electricity supply comes for more than 70% from fossil fuels. So check with your electricity provider. And if you live near flowing water and you powered your electric car from a water mill, you're a true green hero.

While you are crunching the numbers for your particular case, you might as well include the following consideration: The battery suffers from both cold and hot weather. At 32F (0C) count on a reduction of the car's range up to 30% compared to the "ideal" temperature of 77F (25C). Above that temperature, the battery lifetime starts to deteriorate; at 104F (40C) the battery's life is half that at 77F. So this suggests that electric cars will do best in temperate climates such as in the Pacific Northwest. In Minneapolis MN winters, the battery capacity and therefore the travel range will suffer; and Phoenix AZ summers will shorten the battery life considerably.


The rest of this post is about how CelloMom arrived at the red numbers in the modified sticker, above. You don't have to take CelloMom's (or anyone's) word for any number: CelloMom includes links to all the places where she found numbers, so you can check her math.

What MPG-e means.
What's an mpg label doing on an electric car? The MPG-e (miles per gallon equivalent) was chosen because consumers wanted an apple-to-apple comparison with gasoline-powered cars. In, truth, the natural unit for electric car efficiency is the kWh/100mi (kiloWatt-hour per 100 miles; see Tom Murphy's excellent piece on decoding fuel efficiency). But many of those who were polled by the EPA were confused by the kWh. So we got our easy-on-the-brain label. But the devil is in the detail of the translation.

To find the MPG-e for an electric car, take the battery capacity, i.e. how much energy can be stored in it, and divide it by the car's range (this ratio is measured in kWh/100mi). That battery energy is compared to the energy released (in the form of heat) when you burn a gallon of gasoline. Not all gasoline is created equal, but the EPA has chosen a standard of 115,000 BTU (British Thermal Units) per gallon of gasoline, or 33.7 kWh. Confused? See CelloMom's quick rundown on units for energy.
1 / kWh/mi = 33.7 MPGe

The Nissan Leaf is found in EPA tests to have an electric efficiency of 34kWh/100mi, or a gas-equivalent efficiency of 33.7 / 0.34 = 99MPGe. Leaf owners have reported an efficiency closer to 25kWh/100mi which corresponds to 33.7 / 0.25 = 135 MPGe, even better than the 99MPGe stated on the sticker.

That sounds marvellous, no?
BUT- CelloMom just can't help getting that itchy feeling about this. MPG-e as defined above sounds reasonable enough; it is certainly straightforward. But let us just take a step back: what is the whole point of the electric vehicle exercise? Is it not to curtail the emission of carbon dioxide which is a greenhouse gas?

Some, but not all, electricity comes from coal, the burning of which causes the emission of CO2 as well as other nasty gases, like sulphur compounds that give rise to acid rain. So let us follow, step by step, the path of the electricity, before it makes it way into your car battery, and let us trace it all the way back to its source.

Charging efficiency.
Let's start from the battery side. Have you ever felt the charger of your laptop after an hour's use? It's a little warm to the touch, and that's because the conversion from 110V AC from your wall socket to the DC battery is not 100% efficient. Nissan Leaf owners report a charging efficiency of 90% for a "good" charger; the remaining 10% serves to heat your garage.

Transmission efficiency.
Similarly, not all the electricity that leaves the power plant makes it to your home; there are losses in the transmission lines and in the distribution stations that direct the current to the various neighbourhoods, etc. The total transmission & distribution efficiency in the US is about 93%.

Generation efficiency.
For power stations running on fossil fuels such as coal or natural gas, the efficiency is around 33%. In a coal-powered plant, the coal is crushed into fine particles and burned to heat water that drives steam turbines that generate the electricity. It's a really complicated and rather magnificent piece of engineering, and there are losses at every step, adding up to 67% of the original input energy.

Production efficiency.
Of course, the coal doesn't show up at the power plant door by itself: it needs to be mined (and sometimes transported, although many coal-powered plants are built close to the mines to cut transportation costs). For coal, the energy return on investment (EROI) is 80, that is to say it takes the energy of one pound of coal to get 80 lbs of coal to the mine mouth; i.e. the production efficiency is 80/81 = 98.8%. Natural gas has EROI of 10, so a production efficiency of 10/11 = 90.9%. (Incidentally, solar energy has a pretty low EROI, just 6.8, because it takes a lot of energy to make the high-purity silicon that goes into a typical solar cell. Hydropower gets the best efficiency, EROI > 100).

As CelloMom has said before, it you live next to swiftly flowing water and powered your Nissan Leaf from a water wheel, you're a green hero. The rest of us average Joes will have to plug in our electric vehicles into the socket, and the average socket still gets its power from conventional means. In the US, about two-thirds of all electricity is generated by burning fossil fuels. Table 1 below lists the carbon dioxide emissions for each type of fuel at the generation point, as well as the average total CO2, with ("Total") and without ("Plant") accounting for the energy cost of production.


Table 1: CO2 emissions in US electricity generation from various primary fuels.

Fuel Type % Plant CO2 emission
g/kWh (lbs/kWh)
Total CO2 emission
g/kWh (lbs/kWh)
Coal 45 961 (2.117) 973 (2.142)
Gas 23 597 (1.314) 657 (1.446)
Nuclear 20 0 9
Hydropower 6 0 4
Other renewables 4 0  
Petroleum 1 869 (1.915) 941 (2.075)
Other 1    
TOTAL 100 613 (1.350)  
Wind   0 10
Photovoltaic   0 100


On average in the US, electricity generation causes CO2 release of 613 g/kWh (1.350 lbs/kWh) at the plant, not including the carbon released in the production stage of the various fuels. So the carbon footprint of a Nissan Leaf owned by an average US electricity customer, at 25kWh/100mi, comes to 0.25 * 1.350 = 0.338 lbs/mi.

What does that mean, 0.338lbs/mi?
The average gasoline engine releases 19.4lbs CO2 for every gallon it consumes, so the carbon-equivalent fuel economy, or MPGc if you will, is (19.4 lbs/gal) / (0.338 lbs/mi) = 57 MPG-c. This is what the EPA sticker should really say: 57 MPG-c, and 0.338 lbs/mi (153 g/mi) CO2 emission. After all, that's what this is all about: getting a handle on our total CO2 output.

CelloMom wants to emphasize at this point that these are average numbers, and that they paint the best possible picture for the average US user. We use the 25kWh100mi efficiency reported by users rather than the lower official efficiency of 34kWh/100mi. CO2 emission in the fuel production stage has been ignored. The 20% contribution from nuclear sources is quoted at operational value, including the construction of the nuclear power plant, but excluding the cleanup costs of the now rather old plants (that nobody is very eager to discuss).

In reality, the mix of primary energy sources for electricity varies from state to state, with the largest contribution coming from, for example: 69% natural gas in Nevada, 56% nuclear in New Jersey, 58% hydroelectric in Oregon, and so on. Your particular utility will have its own profile.

To make an entirely fair comparison with gasoline-powered cars, one also has to take into account the efficiency of production and delivery of gasoline: the "well-to-pump" efficiency is about 0.83%, so the total carbon emission is 20% higher than the fuel economy would suggest. To find the true carbon-equivalent mpg of a gasoline-powered car, find the real mileage as reported by real-life users, MPG-r, and multiply that by the production efficiency of 83% (the same number for both gasoline and diesel): MPG-c = 0.83 * MPG-r.

Armed with this information, we can now put together a picture for any given car. A few examples are included in Table 2 below, which shows the "official" fuel efficiency as stated in the carmaker's promotional material, the "real" efficiency as reported by actual users (MPG-r), the carbon dioxide emitted per mile of travel, and based on that, the carbon-equivalent fuel economy (MPG-c). The VW Golf numbers are for the 2001 2.0L gasoline model.


Table 2: Fuel Economy, Carbon Emission; US averages.

Make/model Official
Nissan Leaf 99 MPGe
34 kWh/100mi
135 MPGe
25 kWh/100mi
57 mpg
Toyota Prius 51/48 mpg 50 mpg 0.47 42 mpg
Honda Fit 27/33 mpg 35 mpg 0.67 29 mpg
Honda Jazz 36/51 mpg 40 mpg 0.58 33 mpg
VW Polo diesel 69 mpg 57 mpg 0.47 41 mpg
VW Golf (2001) 18/20 mpg 20 mpg 1.17 17 mpg


Among the cars in Table 2, the carbon-equivalent fuel economy is indeed highest for the Nissan Leaf at 57 MPG-c, but not by as much as suggested by the 99MPG-e on the EPA sticker.

The hybrid Prius does pretty well, at MPG-c = 42 mpg, closely followed by the diesel-powered VW Polo.

And this is where CelloMom's looks her past actions in the eye and admits that her current car, a 2001 VW Golf, is scandalously un-frugal, especially for something that size, belching more than a pound of CO2 at every mile traveled. CelloMom hangs her head in shame. (In fairness to the Golf, the 2012 version is quite a bit more frugal at MPG-r up to 50mpg).

Nothing like a bunch of hard numbers to rub your nose into the cold facts.

October 5, 2011

Review: Ford Fusion / Ford Mondeo

When CelloMom helped her dad look for a new car, we came across the European Ford Fusion, a cute and versatile mini-MPV just 4m long. It turns out the US Ford Fusion is a different beast altogether: it is a "mid-size" car, most closely related to the Ford Mondeo; in Europe the latter is labeled a "large family car". Go figure.

After befuddling herself for a while over the nomenclature, CelloMom has decided to stick to her own size indication: length of the car only. No matter what anyone chooses to call it. After all, a name is just a name. A length is a measurement. US Ford Fusion (pictured below): 4.84m; European Ford Mondeo (pictured left): 4.78m. Simple.

So then, about the Ford Fusion: In the US it replaced the Ford Taurus (which has surreptitiously grown into the "full-size" class), and in Latin America it has replaced the Ford Mondeo, which has also been very popular in Europe. Don't ask CelloMom to describe the differences in the body: they both look like large sedans to her. The grilles are slightly different; the Mondeo has some extra LED lighting up front. The Fusion is a bit heavier, and probably has cushier seating.

Under the hood are the differences that matter to CelloMom. The Fusion (US) comes with a choice of 2.5L, 3.0L and 3.5L gasoline engines, all of the Duratec variety (and the 3.5L of the egg-breaking variety), with combined cty/hwy mileage of 26, 23 and 21 mpg respectively. There is also a hybrid version, which gets 39mpg combined cty/hwy mileage. The Mondeo comes with 1.6L and 2.0L gasoline engines, and 1.6Lm 2.0L and 2.2L diesel engines. As with many other cars, the European versions come with smaller engines than the American versions, with no overlap in the ranges of engine volume.

The table shows a comparison of the Fusion 2.5L, the Fusion Hybrid, and the Mondeo 1.6L diesel with start/stop technology. All of these versions are new enough that there is no data yet on actual fuel economy, but comparing to similarly sized engines made by Ford, CelloMom estimates that the Fusion 2.5L gets around 27-28mpg, the Fusion Hybrid about 41-43mpg, and the Mondeo 1.6L diesel close to 50mpg. That is really more than decent in a car this size. Allright, it's excellent.

To get a feeling for how much this car would cost if sold in the US, remember that diesel versions of the same trim tend to be more expensive; the "Edge" trim level with 2.0L gasoline engine starts at £18,295. CelloMom's rough estimate for the 1.6L diesel version would be in the $20,000 - 22,000 range, in any case well below the MSRP for the Fusion Hybrid, which would make the total cost of ownership for the Mondeo 1.6L diesel significantly lower than for the Fusion Hybrid. This is quite apart from having (slighly) lower carbon emissions.

For CelloMom personally, frankly this car is too large. It's one of many cars in which, when the front door has swung open completely, CelloMom finds she has to climb out again to catch the door handle: her arms are simply too short. CelloDad would have no problem, but the priority should really go to the arm that does most of the driving, in this case CelloMom's.


Ford Fusion / Ford Mondeo

Fusion Fusion Hybrid Mondeo
Type 2.5L Duratec Hybrid 1.6 DV6 TDCi
Start/Stop 5-door "Edge"
Year 2012 2012 2012
Emissions rating
MSRP $ 19,645 $ 29,395 £ 19,895 ($30,800)
CelloMom Rating
Fuel Economy:
City/Hwy quoted 22 / 32 41 / 36
Avg. quoted 25 39 55 mpgUS
Avg. actual
Engine 2.5L 16V 4-cyl 2.5L Atkinson
I-4 Hybrid
1.6L DV6 TDCi Start/Stop
Power 175 HP @ 6000 156HP @ 6000 115 HP
Gears 6-spd manual e-CVT (auto) 6-spd manual
Fuel Reg. unleaded Reg. unleaded Euro unleaded
Length, mm(in) 190.6in (4.84m)

190.6 in

Width, mm(in) 80.1 in (2.16m) 80.1 in 2092mm
Height, mm(in) 56.9 in (1.45m) 56.9 in 1500mm
Weight, kg(lbs) (3720) 1435 (3164)
Trunk volume, liters(cuft) 16.5cuft (467L) 11.8cuft (334L) 540 / 1560 L
Turning radius, m(ft) 37.5ft (11.4m) 11.6m
Top speed, kph(mph)

October 1, 2011

Units for Energy

The Sami of the Scandinavian polar circle region, also known as the Lapps, have hundreds of words for that which is so important in their lives, snow. Similarly, energy, which is so important to all humans, comes in a bewildering array of flavours, depending on its use. But unlike snow, energy is energy, and to go from one unit to the other just take the right translation.

Don't miss the fascinating list of energies, covering such things as the kinetic energy of a flying mosquito (10-7J); the kinetic energy of a person jumping as high as they can (390 J); the energy to accelerate a 4-ton truck to highway speed (0.9 MJ); the food energy in a Mars Bar (1 MJ) whoa!; the annual electricity consumption in the US in 2005 (1.37 x 1019J); the total solar energy striking the face of the earth daily (1.5 x 1022J).


1 cal = 4.184 J
It all started when a Frenchman, Nicolas Clément, defined the calorie (cal) as the energy it takes to heat a gram of water by one degree Celsius.

1 Cal = 4184 J = 4.184 kJ
The food calories we think about a lot is actually the kilocalorie (Cal), the energy it takes to heat a kilogram of water by one degree Celsius. So Cal = 1000 cal.

1 BTU = 1055 J
Not to be outdone by the French, the rivals across the Channel introduced their own version, the British Thermal Unit (BTU), which is the energy it takes to heat a pound (0.454kg) of water by one degree Fahrenheit. BTU is how energy is measured in the world of heating and air conditioning in the US. For instance, the burning of a US gallon of gasoline releases 115,000 BTU of heat.

1 therm = 105.5 MJ
Consistently eclectic (and to avoid having to use the continental prefix kilo), the British defined 1 therm = 100,000 BTU, perhaps taking a hint from the Lakh of the Indian subcontinent. You know the therm from your monthly gas bill, for one therm is about the energy released at the burning of 100 cubic feet of natural gas.

1 J = 1 J
The metric unit of energy, the Joule, is the amount of energy, or work, done by applying a power of one Watt over a time of one second:
1 J = 1 W.s . Boring, but functional.

1 kWh = 3.6 MJ = 3.6 x 106J
A kiloWatt-hour is a thousand Watts of power applied for an hour. Running your 1200 W hairdrier for half an hour makes your electricity meter go forward by 0.6 kWh. Turning on a 100W lightbulb for 3 hours is good for 0.3 kWh.

1 ton TNT = 4.184 GJ = 4.184 x 109J
Exploding one gram of tri-nitro-toluene releases an energy of 1000cal (or 1Cal), so a ton of TNT releases a million times that amount of energy.

1 eV = 1.6 x 10-19 J
One electron-Volt is the kinetic energy acquired by a free electron that is accelerated through an electric potential difference of one Volt. Electric car enthousiasts: a Nissan Leaf's fuel efficiency is 0.25 kWh/mi = 5.6 x 1024 eV /mi. You gotta have 5.6 yotta-eV to make one EV go one mile.

1 boe = 6.1 GJ = 1.7 MWh
One Barrel of Oil Equivalent is the energy released by burning a barrel (42 US gallons) of oil.

Gasoline gallon equivalent
This is complicated, and the subject of another post.