How much horsepower do you need?

One very important item in the "Performance Specification" page of any car is the power of the engine. CelloMom explores what exactly you need all that horsepower for, and how much is enough.

Let's put the conclusion right here: 76HP is enough to cruise the nation's interstate highway system at 65 mph in a large family sedan (except in high winds). Read on for details, and to check my math.

To tell the truth, a single horse can be hitched to a car and move it forward. Heck, even a scrawny child like CelloPlayer could push a car. CelloMom herself has done it often enough, to help her dad start the car when the battery has run down. CelloMom's dad believed that jumper cables were for helping other people jumpstart their car.

Of course, a child-pushed car will only go as fast as the child can run. Same for the one-horse car. But even an infinitely swift horse will not be able to pull a car faster than some maximum speed. It's because of air resistance, which you can feel as in your face when you bike at decently high speeds.

 

Aerodynamic resistance.

Inside most cars you don't feel the wind, but the air resistance is there nonetheless, and it is the larger because the car has a larger area facing that wind than you and your bike together. The power required to match the air resistance, or drag, is:

P_air = ½ C_d A ρ v³

An equation is worth at least a thousand words! This one is pretty straightforward, let's look at its parts:

C_d is the drag coefficient (that is, a fudge factor, that depends on the shape of the car)
A is the frontal area of the car
ρ = 1.20 kg/m³ is the density of air
v is the speed of the car.

If you look at the equation above, at standstill (v=0), there is no air resistance. But once you're moving the power rises rapidly, as the speed cubed. This means that in order to go 50mph on a country road, your engine has to put out 8 times the power it does as when puttering around town at 25mpg, just to deal with the drag.

The larger the car, the larger the frontal area A, and the larger the drag. For a truck, A is seriously larger than for a Mini.

A truck's drag coefficient is also large, close to C_d=0.6 or more, because a truck is basically box-shaped. Cars try to resemble a bullet in their outline, or better yet, a fish, in order to minimise the drag coefficient while still harbouring a decent space inside. For many passenger cars, C_d~0.3.

Finally the density of air is quite small, so you don't feel the resistance until speeds get fairly high. A medium like water has a much higher density, ρ= 1000 kg/m³, so the resistance is that much higher, as we all know when we try to walk in a swimming pool.

We're ready to try out some numbers. In the following, we'll consider the "vanilla" largish car, one that weighs 4000 lbs with a full load of a few passengers and luggage, or about 2000 kg. This car is 2m wide and 1.5m tall (think of a Toyota Camry or a Honda Accord). Oh, and CelloMom does everything in metric, because that way all the equations are simple. The only concession is that in the end we will convert Watts (W) to Horsepower (HP): 1HP = 746W. Sigh.

Let's take the vanilla car out on a highway cruise, at 65 mph or 30m/s. At that speed, P_air = 14.6 kW = 19.5HP. Speeding at 80 mph takes nearly twice as much power: P_air = 36HP. Think of that next time your right foot becomes heavy.

Once on a camping trip in a 1985 VW van that belonged to CelloMom's dad, we met a hurricane. The wind was coming in straight at the windshield, but we had a ferry to catch so we kept going on that highway. The VW's frontal area was large because of its height; its boxy shape gave a large drag coefficient; it had a 1.8L boxer-type engine. All in all, we could go no faster than 60 mph, even with the accelerator pedal pushed all the way down. But considering the wind was in our faces, the effective total wind speed was probably close to 100mph. (Arrived at the shore, we found that the ferry was closed down for the day).

 

Rolling resistance.

Let's slow down a bit and get off the highway to mull things over. As you slow to pedestrian speeds the air drag is very small, but coasting in neutral your car will eventually come to a stop. That's because of friction on the car's tires, which deform elastically so you don't have to feel every pebble and pothole on the road. The power to overcome the rolling resistance is:

P_rr = C_rr mgv

Here v is the speed of the car,
g is the specific gravity, g=10 m/s²
m is the weight of the car
C_rr is the coefficient of rolling resistance, another fudge factor.

C_rr depends on the size of the wheel and the material of the tire and the road surface. If you've ever chased a marble or a ball bearing down the pavement you know that hard round things have a small C_rr: they can keep going forever. Try it with a steel ball bearing in a steel mixing bowl from the kitchen (C_rr less than 0.001). Carriage wheels were made of wood with a band of iron on the outside: that made it easy for the horse who had to pull the carriage - but the noise! And the passengers tended to get their teeth rattled inside their heads. The rubber on a car's tire takes away that nasty effect by absorbing the impact of road roughness, but that means the rolling resistance is also larger, C_rr = 0.01 for most car tires.

P_rr also increases with the weight of the car because after all, it's gravity that does the job of mushing the tires onto the road surface.

For our vanilla car going at 65 mph, P_rr = 6 kW = 8HP, or about 40% of P_air. This is one reason why fuel-efficient cars tend to be lighter: decreasing m also decreases P_rr.

But still: if you stick to the speed limit, you never need more than 28HP to move your family sedan on an interstate road trip. On flat interstate highways, that is. But this country is not flat everywhere, thank goodness. Its hills and mountains are as much part of its beauty as its vast plains.

 

Life on a slope

There are uncounted hilltops from which you can enjoy the view; but to get to the top, you have to drive up that slope. Now your engine is not only dealing with air drag and rolling resistance, it also needs to hoist your car and its contents up the slope, against gravity. The power required to do that is

P_g = mgv sinα

As before, m is the total weight of the car
g is the specific gravity
v is the car's speed
α is the angle the road surface makes with the horizontal.

It makes sense that P_g increases with m, the car's weight, and that it is zero when the road is horizontal, that is α = 0.

But notice that P_g increases with v! That is to say, in the absense of rolling resistance, you can get up that hill even with a puny power; it just takes longer. This is why loaded trucks slow down on uphill stretches of road.

Not all of us have all day, so one of the specifications for the construction of US interstate highways is that the grade must be 6% or less, that is, for every 100 yards travelled horizontally, the vertical rise is 6 yards or less. To a good approximation, sinα < 0.06.

So heading for a hilltop at 65mph on an interstate, the engine is asked to put out at most 36 kW = 48 HP to deal with the rising altitude. If you include the 20HP for the air resistance and 8 HP for the rolling resistance, you arrive at a Grand Total of 76HP. 76HP is enough to cruise the nation's interstate highway system at 65 mph. If you are generous with yourself you can double that and put a 150HP engine in, which lets you live a little, and go 80mph on most interstates with a fully loaded car. It also helps in very windy conditions, like a hurricane.

Who needs 250HP, even 350HP in a family sedan?
Germans on the Autobahn, that's who. Once, after a business visit to a company in the south of Germany, CelloMom was kindly offered a ride to the airport by her host, a German named Klaus, who drove a Mercedes station wagon. We were calmly talking business, until CelloMom glanced at the meters and realised we were going 200kph or nearly 125 mph. It was a quiet stretch of German Autobahn at a quiet time of day, but passing trucks who were only going 110kph or so, just a few feet away in the next lane, was a little nervewracking. At the airport, CelloMom thanked Klaus politely but climbed out of his car slightly shaken, resolving to take the train next time.

At Klaus' cruising speed of 200kph, or nearly 60 m/s, P_air = 160HP and P_rr = 16HP. If the uphill slope on that Autobahn was at most 6%, it would require an additional P_g = 96HP from the engine. So Klaus would need an engine with at least 272HP, and 350HP would not be too much. If he habitually drives faster, he might need more horsepower in his engine. But we're talking white-knuckle speeds over 125 mph.

There is one other reason to have huge amounts of power under the hood, a reason beloved of jackrabbits and their close relation, the average human male everywhere.

 

Acceleration

Ah, sweet acceleration! That feeling that you're going somewhere. One of the specs prominently featured, especially for cars at the high end of the power spectrum, is how long it takes to accelerate the car from 0 to 60mph. For any self-respecting muscle car, this time is quite a bit less than 10 seconds. Let's see what that means for the power requirement.

The energy of a car travelling at a speed v is E = ½ mv² (with m the mass of the car, also known as weight). Our 2000 kg car going 60mph would have an energy of E = 719 kJoules. The power to accelerate this car to 60mph in time t is P= E/t, or the other way around, t = E/P. This tells you what you already knew: the larger the power, the shorter the acceleration time. At 100HP (75kW), t = 9.6 seconds. At 400HP, the time is shortened to t = 2.4 seconds.

At accelerations like that, you can use your car to hug your friends: you merely put down your foot on the accelerator, and your friends are pressed into the passenger seat. You can get away from the traffic light ahead of anybody else - this is really what it's all about, right guys? You can jump into highway traffic without having to wait for the safe gap between cars. You can cause the groceries to rattle around in the trunk and the eggs to slide and go splat against the rear wall. You can wreak havoc on cellos and other delicate musical instruments.

CelloMom can live without all this sound and fury. CelloMom needs her eggs to come home whole, and needs to protect the rented cello. And CelloMom has learned (the hard way, it should be said) that leaving on time beats driving like a jackrabbit by a long shot, preventing wear and tear both on the car and on the nerves.

And CelloPlayer would ask, who needs 350 horses? All you need is one horse. Add a saddle, you're set to go.

 

 

You may also like:
1. What's so clean about diesel?
2. Why the new CAFE standard is just my cup of tea
3. How to buy a gas sipper for less
4. Have your Cake and Drive it Too: of Fuel Economy, Performance, and Moms

 

Why are cars so small outside the US?

A science fiction story once reflected that the planetary diaspora of human vehicles still basically followed the size standards set by the Romans when they built Europe's first interstate highway system. This is true of NASA's Mars rover "Curiosity" which is to be launched later this month.

It is true of earth-bound passenger cars built today, most of which would have no trouble fitting in the grooves worn by Roman ox carts and war chariots, such as the ones found on the stone-paved streets of Pompeii.

The legacy is inescapable, even for Americans who are said to like everything big: houses, TV screens, softdrinks cups - and cars. American cars grew steadily larger until they became the behemoths of the early 70s. After the oil crisis, they suddenly became smaller, but over the decades since then they have put on volume and weight again, while elsewhere in the world cars have stayed relatively small.

Many governments responded to the 1973 energy crisis by embarking on a policy of energy conservation, which has led to innovations in the manufacture of gas-frugal engines, and the marketing of smaller and lighter cars. The US has chosen a different path toward its energy security - but CelloMom will refrain from hyperventilating about that.

In the 80s and 90s, Detroit, feeling the heat of Japanese competition, asked for and got limits on car imports into the US. Foreign carmakers responded by importing only their largest models which have the highest margin. It is still that way today: for instance, Toyota has a whole line of tiny cars that are never seen here (in this context, Yaris is not tiny).

Another part of the explanation lies in American geography: the country is simply enormous, and there's plenty of space to spread out. Compare this to the old country, whose cities have grown around a nucleus founded in the middle ages, where the old Roman roads set the scale for the expanding construction. In Asia, the oldest streets are even narrower.

In Europe, high population density and a good public transport network are further reasons that not much space is given to car traffic. Many cities have been re-designed to keep cars out as much as possible. Anyway, who wants to be in a Dodge Caravan negotiating streets that were designed for light horse-drawn carriages? And where would you park the thing?

About parking.

In many places in Japan, the purchase of a car requires not only the financing, but also proof that you have a parking space for your future conveyance. There is a good reason for this rule: Even outside congested Tokyo, space is at a premium. CelloMom once spotted a minivan parked in a carport outside of Kochi. Its right-hand outside mirror had been folded in, and was virtually touching the carport wall. On the left (driver) side, there was about 8 inches of space. Either that driver was really skinny, or s/he climbed out through the rear hatch.

In the Dutch neighbourhood where CelloMom grew up there is no space for carports, just roadside parking. You couldn't park a Prius there. Well, you could, but the neighbouring spot had better contain a smaller car. Come to think of it, there are a bunch of really small cars in this neighbourhood, like the Ford Ka, the Peugeot 107 and the Toyota Aygo, the ones that fit very well in those parking spaces.

CelloPlayer went out with a measuring tape and found that those parking spots were just 84" x 176" (that's 7' x 14'8" and that IS a bit small; in most of Europe, a parking spot is around 8' x 16'). Once back in the US, we went out to measure the parking spots at those newer malls with the mega-stores: those spots are 9' x 18'.

The picture above shows three adjacent parking spots in CelloMom's old neighbourhood, and one parking spot at a US mall, all outlined in yellow dashed lines. Where a Honda Fit would "fit" just fine (left-most car in the picture) in the tiny spaces, a Dodge Caravan would spill over on all four sides (middle car in picture). Providing small parking spaces is just another way to apply pressure to keep gas guzzlers out of residential neighbourhoods. That same Caravan fits comfortably at a US shopping mall (rightmost car).

Even so, we've come a long, long way: the Caravan is dwarfed by some of the cars that used to be the US norm. One example is the Buick LeSabre: fully two feet longer than the contemporary minivan, it would stick way out among a row of Siennas and Odysseys and such. When the LeSabre first came out in 1959, you could only buy it with a 6.0L V8 engine that puts out 250HP. In the early 1970s one of the options was a 7.5L V8 engine. After that the engines got smaller and smaller, bucking the trend for many other models, until the last LeSabre was delivered in 2005 with a 3.8L V6 engine - but one that still delivered 205HP.
Take heart: engine efficiency has come a long way as well.

Responding to relentless pressure from governments that do subscribe to the Kyoto protocol, many car manufacturers outside the US have developed smaller, more frugal engines that still pack a punch: for instance, 211HP is what's delivered by the 2.0L TFSI gasoline engine in the Audi A4 Avant - you don't need a 3.8L V6 engine to do the job. Smaller engines are pushing fuel efficiencies well past 50mpg, even without hybrid technology, keeping down the purchase cost. For the short to medium term, CelloMom would put her money on those, rather than on the yet-to-be-developed but already expensive electric cars US carmakers like to push.

Review: Citroën C4 Picasso / Grand Picasso

Here is a moderately sized MPV with plenty of space, a panoramic view, and outfitted with a range of engines that get up to 42mpg in real life: what's not to love?

Visit the Citroën website: here is a place that is decidedly different from most auto websites in the US. The feel of it is just different. Once your stunned eyes have adjusted to its aesthetic, hover your mouse over the menu item that says "Véhicules" and find the C4 Picasso. Among the current fleet of cars that sink into vanilla anonymity in their drive to resemble one another, this is a car that is distinctive! You can spot it a mile away.

Those who make snide remarks about how Toyota Prius resembles an egg have never seen the Citroën Picasso. Before they put on that overhang in the back, the Picasso really looked like an egg. But don't snicker before you've actually had a chance to climb into one: the panoramic windows, which continue on the roof (!), are a revelation.

Two summers ago, CelloMom decided to take the children on a camping trip in France. CelloDad, who likes the room service kind of holiday, stayed behind, but grandpa, who adores camping, came along. It was a last-minute thing, so CelloMom went to the car rental in Holland and asked for something that would fit four people plus camping gear. What she got was the slightly larger version of the Picasso, the Citroën C4 Grand Picasso, longer by nearly 9 inches and taller at the back, and not nearly so egg-like in shape (pity). There was an optional third row of seats but we kept that folded down to make space for the gear.

The windscreen is enormous. As you sit behind the wheel, its top edge is out of your field of view. The side windows continue to the very front corners, so you get the feeling of driving in a bubble.

The children loved the big windows in the back. Too many cars have rears which are squished for the sake of aerodynamics, and the windows in the back row really suffer from it. Not so in the Picasso: the windows, even in the back, start low enough that a child can look out without that nose-on-the-glass trick. And they go up. Way up. And continue on the roof. That roof window really bailed us out on more than one occasion, because the children were able to see the road signs and provided excellent navigation services from the back seat while grandpa, who had forgotten to bring his reading glasses, was still squinting at his map.

At 4.59 metre length (181 in) this was not your lumbering US-style MPV: parking in old French towns with narrow stone-paved streets was no problem. But inside, there was plenty of space to be comfortable for long drives. We traveled west through Normandy and Bretagne, eating like sultans between the fossil hunting, church viewing and beach visits. At most campsites, the check-in routine included putting in an order for baguettes and croissants which would arrive the next morning, fresh from the local bakery and still warm. A civilised way to camp!

CelloMom and the children would retire in the tent, and grandpa would install himself in the car: you can fold down the second row of chairs to make a cavernous flat-floor place to spread out a sleeping bag, and watch the stars in warmth and comfiness.

The rental Grand Picasso came with an automatic transmission. While CelloMom usually prefers a manual transmission, in this case the clever EGS (Electronic Gearbox System) actually delivered slightly better fuel economy than the manual transmission (see table below), partly because the automatic version has a turbo-booster. The gasoline version gets an official fuel efficiency of 6.9 L/100km (34 mpg) for the manual version, and 6.7 L/100km (35 mpg) for the automatic. The latter's 156HP was more than enough to negotiate the hilly country in Bretagne with a full load. The similarly-sized diesel engine gets 48 mpg officially, 42mpg in real life.

So then: seats for up to 7 passengers, amazing view, space for grandpa to stretch out (never mind the cello), 42mpg - What's not to love? Well, unlike the Opel Meriva, the Grand Picasso doesn't have a built-in bicycle carrier. Then again, it has a roof-length rail ready to receive a bike rack. CelloMom went to a Peugeot dealer and sat in a Peugeot 5008, which shares the Picasso's platform, and was impressed by the way you can keep an eye on your bike even as you're zipping along the highway. (The demo bike in the photo is, of course, a Peugeot). Allright, then, perhaps one doesn't need a built-in bike rack.

In the UK, the brand is pronounced "citron", even though the name in French has three syllables. Without the umlaut on the e, you get the Dutch word for "lemon". Perhaps it is the unfortunate name that has kept this brand mostly inside Europe. But make no mistake: the Grand Picasso is no lemon. It is, on the contrary, a highly desirable family car, versatile, fun to drive, and best of all: gas-frugal.

 

Citroën C4 Grand Picasso HDI-110, auto vs. manual

Trim	C4 Tendance	C4 Tendance
Type	EGS Auto	HDI 110
Year	2012	2012
Emissions rating	Euro5 "B"	Euro5 "B"
MSRP	€ 20,905 pre-tax ($ 28,700)	€ 19,883 pre-tax ($ 27,300)
CelloMom Rating
Fuel Economy:
City/Hwy quoted	5.4 / 4.6 L/100km	6.5 / 4.6 L/100km
Avg. quoted	4.9 L/100km (48 mpg)	5.3 L/100km (44 mpg)
Avg. actual	50.1 mpg_imp (42 MPG)	48.5 mpg_imp (40 MPG)
Engine	1.6L EGS stop&start	1.6L HDI
Power	112 HP @ 3600rpm	112 HP @ 3600 rpm
Gears	6-spd auto	6-spd manual
Fuel	Diesel	Diesel
Length, mm(in)	4590 mm (180.7 in)
Width, mm(in)	1830 mm (72.0 in)
Height, mm(in)	1710 mm (67.3 in)
Weight, kg(lbs)	1495 kg (3296 lbs)
Trunk volume, liters(cuft)	576L (1951L w 2nd row seats down)
Turning radius, m(ft)
Top speed, kph(mph)	182 kph (113 mph)	181 kph (112 mph)

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)

Car	Vehicle Weight (lbs)	Mfg. Energy (GJ)	Real Fuel Efficiency (MPG)	Fuel Energy (GJ)	LifeCycle Energy (GJ)
Toyota Prius	3042	119	50	436	545
Toyota iQ	1808	60	43	506	566
VW Golf TDI 1.6L	2998	99	50	497	596
VW Golf TDI 2.0L	2994	99	40	621	720
Honda Fit	2489	82	35	622	704
Honda Odyssey	4337	143	20	1089	1232
Audi A4 Avant 2.0 TFSI	3461	114	24	908	1022
Audi A4 Avant 2.0 TDI	3527	116	39	637	753

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.

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.

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	2.0L 4-cyl, 16vlv	2.4L 4-cyl, 16vlv	3.5L V6, 24vlv
	41 mpg	31 mpg	27mpg	24 mpg
US			X*	X*
Japan		X	X	(X*)
UK	X	X	X
Netherlands	X	X	(X)
Brazil		X*		X*

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)
Engine	2.4L 4-cyl 16-valve DOCH i-VTEC	2.2L 4-cyl 16-valve DOCH - iDTEC
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)

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	CO2 lbs/mi	Cost / 100mi	MSRP
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.

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)
CelloMomRating
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 i-STOP
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)

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.
So:
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 Efficiency	Real Efficiency, MPG-r	Total CO2 lbs/mi	CO2 Equivalent MPG-c
Nissan Leaf	99 MPGe 34 kWh/100mi	135 MPGe 25 kWh/100mi	0.338	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.

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	4784mm
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)

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.