Saturday 4 September 2010

A tank full of petrol ("gasoline," if you prefer), and what it means

We bought petrol today. It's quite a novelty for us, as we don't do it very often. The last time we bought petrol was way back on August 27th... 2007.

I've mentioned before that we're not really all that enthusiastic about driving, but today we made a short journey in our car and needed to fill up the tank.

It made me think: what exactly have we bought today ? Our tank full of fuel came to a bit more than 36 and a half litres. 36.5 l of petrol weighs about 26 kg. Burning that one tank full of petrol will put about 84 kg, a little more than my own weight, of CO2 into the air. That's the effect from just one tank full of petrol, which according to the manufacturer is supposed to be enough to drive around 500 km.

Petrol is amazing stuff. It has an energy content of 9.7 kWh per litre, so today we bought 355 kWh of energy for our 53 euros. The car consumes about 0.7 kWh produces 0.17 kg of CO2 per km driven.

A few years back, someone who set a world record by cycling over 1000 km in 24 hours calculated that his average power output was about 115 W for the entire 24 hours. That's someone at the absolute peak of what is possible, and his body generated about 2.7 kWh over a 24 hour period.

In light of this, I think it's reasonable to say that an averagely strong person doing an 8 hour shift at a physically demanding job would expend no more than 1 kWh per day at work, so we could say that in our tank full of petrol we've bought the equivalent of someone working hard nearly every day for an entire year, including weekends and almost all holidays. This cost just 53 euros. That really is a bargain.

Car manufacturers put a lot of effort into insinuating otherwise, but cars are actually quite amazingly inefficient. It seems no-one is really all that interested in making them any more efficient. Petrol provides an awesome amount of energy for a remarkably small cost, and pushing gently on the accelerator makes a car zoom along quite nicely. Anyone who's ever pushed a car any distance knows that there is nothing particularly efficient about it.

There is much hype over electric cars, even though they do little more than to shift the source of the output of that CO2 elsewhere. Many power stations are still coal power stations. In fact, many new coal power stations are still being built, all around the world.

When you burn coal at a power station you get only about 2 kWh of energy per kg of coal burnt. If instead of filling up a petrol car today we had charged batteries of an electric car with the same amount of energy by using electricity generated by coal, it would have required the burning of no less than 177 kg of coal, producing a whopping 518 kg of CO2 in the process. That's over 6 times the amount produced by burning petrol directly in a car. An equivalent electric car therefore would still consume about 0.7 kWh but produce over 1 kg of CO2 per km driven. That's being quite generous, as you never get so much energy out of a battery as you put into it when you charge it. With NiMH batteries, for instance, you get back out only about 2/3rds of the energy you put in - under ideal conditions.

Electric bicycles are also not so innocent as many people think. According to this pro electric bike website it costs 1.8 kWh in electricity to charge an electric bike battery for a 20 mile (32 km) range. That's nearly 1 kg of coal per charge. Even with their figures, which like mine for electric cars ignore the problem of inefficiency of rechargeable batteries, this indicates that an electric assisted bicycle, powered by electricity from coal, consumes about 0.05 kWh and produces about 0.08 kg of CO2 per km ridden.

Yes, so electric bikes, if charged by electricity generated by coal (in Australia, for instance, 80% of electricity comes from coal, and the majority of the rest from other fossil fuels), have a CO2 output per km which is only about half that of an average car with one occupant.

Public transport isn't all that much better either. The average bus occupancy in the UK is only about 9 people. Due to this, figures you can calculate for overall efficiency for the entire bus network are actually remarkably similar to those for single occupancy cars.

The same happens with trains. Only if you assume that electric trains take all their electricity from carbon neutral sources do they look particularly good. High speed trains are remarkably close in emissions to jet aircraft.

Here's a comparison of different passenger transport modes in the US. It doesn't much matter than it says BTU instead of kWh that I've been using. 3413 BTU are equivalent to 1 kWh, so divide these figures by 3413 to get equivalent figures to my calculations above:

As you can see, changing from one of these modes to another is really only about making a small change. Anyone who tells you that one mode of powered transport is incredibly more efficient than another is either selling you something, or is misinformed. However, it's big business (much like oil is) and there are plenty of people with a vested interest in trying to convince you that their motorised car replacement can change the world.

Lots of things are described as "green" but few genuinely are. There is a truly "green" alternative to these modes of transport. It's called a bicycle. No fuel is burnt. No CO2 emissions result. You do have to eat, however from what I've seen, people who drive don't eat any less than people who cycle.

All bicycles are wildly more efficient than powered vehicles. They have to be. Inefficiency makes you tired too quickly (compare pushing a bike with pushing a car). However, some bicycles are still more efficient than others and this makes a huge difference if you need to travel more than short distances. A truly "green" car-replacement for longer journeys looks like this !

The sharp eyed might notice we went to a BP station. I know some people are boycotting them, but frankly it's a waste of time doing so. In my opinion there is very little to choose between oil companies. They're all doing their best to make as much profit as possible from extracting oil from wherever they can get it, and they are all responsible for spills. BP was simply unlucky enough to have had their disaster where it was widely seen and reported upon. Boycotting one chain won't do any good. What really needs to happen is for people to appreciate what an amazing resource both oil and coal are, and to consume less of them.


r s thompson said...

it costs 1.8 kWh in electricity to charge an electric bike battery for a 20 mile (32 km) range. That's nearly a 1 kg of coal per charge.

is that a problem??

if one walked and it would take 4 hours to do tasks where the electric bike could cut task time down to 1.5 hours thus freeing up more time to...figure out more efficient ways of doing things and saving more energy...wouldnt the electric bike have some merit?

townmouse said...

Hmm. Good analysis but I feel uncomfortable about comparing CO2 outputs for buses vs cars. On the few occasions where I can't cycle into town I can take the rural bus, which is a very inefficient one indeed - sometimes I'm the only passenger or one of two or three. Clearly the bus will use more fuel than our little car. Yet it seems obvious to me that if I choose to take the bus, all other things being equal, then at the end of the day there will be less CO2 in the atmosphere than if I had driven, because the bus will make the journey anyway. Of course, in the long term if enough people don't use the bus then it will be scrapped, saving all that CO2, but I don't think anyone would argue that that was an improvement given that the few remaining bus passengers (some of whom are quite elderly) would then be forced into cars or stuck in their homes altogether. Far better surely to encourage more people to leave their cars at home and take the bus.

I'm all for bikes, and use the bus mostly as a last resort, but I don't think we should be playing into the car manufacturers' hands by repeating these statistics emphasising the inefficiency of buses.

2whls3spds said...

Electricity has the advantage that it can be generated by a variety of means; solar, wind, water as well as nuclear. I do agree that coal is not a great source. FWIW I have been playing with the numbers of setting up a small solar generation station on our farm to recharge a golf cart we have. It would not take much to add an electric bicycle and small car to the mix.

Gasoline once burned is gone, and as shown by the BP fiasco is not particularly environmentally friendly during extraction.

Right now I think the best any of us can do is to limit our use of infernal combustion engines and ride our bikes or walk.


David Hembrow said...

r s: No, burning coal isn't a problem at all.

Bikes without electric motors are quicker than those with them (which are limited to 25 km/h). It's possible to build faster electric bikes, but these have higher emissions.

townmouse: It's not "playing into the car manufacturers' hands" simply to write the truth. What am I do to otherwise ? Write a lie about the efficiency of different forms of transport ?

I also don't buy the "it's going anyway" argument. Why will it "make the journey anyway" when it's so ludicrously inefficient to send a huge diesel vehicle on regular long distance journeys just in case someone might use it. Demand responsive buses might make more sense in some of these instances.

However, even the "elderly" are helped by infrastructure which supports cycling. Retired people in the Netherlands make a quarter of all their journeys by bike, while it's not unknown for people of a similar age in the UK to be scared off the roads and trapped in their homes by the traffic.

Brent said...

1) I might suggest a "well-to-wheel" analysis when comparing electric to traditional cars:

(Staring at minute 6)

2) Most people could stand to exercise more, but human power isn't especially carbon friendly. The body is roughly 20 percent efficient, according to Wikipedia. That's about the same efficiency as cars. When the carbon costs of food production are factored in, it may sometimes be more carbon-friendly to eat less and drive, than eat more and bicycle or walk:

3) Electrics can be recharged from clean power sources. Traditional cars cannot. Certainly in California, my part of the world, electrical generation is steadily getting cleaner. I understand it is also so in much of western Europe.

David Hembrow said...

Aaron, Brent: Yes, it's true that electricity "can" be generated by other means, but the majority in the world actually still comes from coal or other fossil fuels (for which the numbers are comparable). The USA is no exception, and California is much like everywhere else in the country.

Also remember that the generating capacity simply doesn't exist for more than a very small percentage to switch to electric cars. If this is to happen you need to build many more power stations. Coal stations are quick to build.

fred_dot_u said...

Even though the numbers present about producing electricity via burning carbon in some form, they are somewhat misleading. Many if not all power plants must operate 24 hours per day in order to keep efficiency, even when no electricity is needed. If someone is charging an electric vehicle during the overnight hours, he is using energy that is otherwise completely wasted.

Along a similar train of thought, an incredible amount of energy is used to create the fuel that is burned in an ICE vehicle and is rarely considered in the calculations.

That said, as a velomobile driver, I much prefer to pedal to my destination rather than to drive either of my electric vehicles.

The speed limitation noted on electric assist bicycles are not universal across the world and in the United States, it's different from one state to another, some with no limits on speed. There is great confusion and misleading information regarding e-assist bikes in the US.

Brent said...

The grid-capacity argument has been much debated without a clear answer. I don't believe, however, that it can support only a "very small percentage." At least one study shows the existing U.S. grid could support about 70 percent of current capacity:

I believe about one-half of California's electricity comes from coal, with the remainder from cleaner sources. Perhaps this snippet may shed some light:

"The Natural Resources Defense Council, using data from the U.S. Department of Energy and the California Air Resources Board, estimates that a typical gas-powered car produces 465 grams of carbon dioxide per mile. Electric cars feeding off of California's power grid produce 142 grams per mile. Electric cars plugged into the grid elsewhere in the country - drawing power from the nation's average mix of natural gas, coal and nuclear plants - produce 214 grams of carbon dioxide per mile."

Erik Sandblom said...

For electric trains, it depends a great deal on how you measure. Either you measure how much power the railway buys from the power company, or you measure how much coal the power company needs to generate that amount.

It seems the numbers from Wikipedia come from the coal the power company needs, which appears to more than double the required amount. In contrast to automobiles, trains are flexible and are commonly run on electricity or diesel, and the electricity can be generated from hydro, nuclear, wind or coal. So it's wrong to assume they always run on coal.

The Transportation Energy Data Book assumes 10 339 BTUs per kwh, page A19, whereas wikipedia's separate entry on BTUs says only 3412.

High-speed trains are not very energy-intensive, I believe that's hearsay. They have a smaller frontal area and more seats than most planes. TGVs have an occupancy rate of 70 %, which is almost twice that of ordinary trains. Flexible ticket prices contribute to that.

David Hembrow said...

Fred: You're right about most power plants having to run 24 hours a day, but not all charging of electric vehicles will be overnight. In fact, the calculation for coal expects that the electricity will be used. The proportion of time that the power station burns fuel to produce energy that no-one uses actually results in everything powered by electricity being proportionately less efficient than I have described here.

You're also right about a lot of energy being used to make petrol in a form that a car can burn it.

Both of these things add up to make bicycles even more efficient relative to other forms of transport than I wrote above.

All other things being equal, efficiency gets lower as speed gets higher. Where electric bikes are allowed to go faster, they will be even less efficient than where they are required to travel at a lower speed.

Erik Sandblom said...

In France and Sweden, 90% of the electricity comes from nuclear or renewables.

Coal doesn't need to be the dominant source.

matt said...

Some of the figures are wrong. e-bikes are more efficient than stated.

Amongst the biggest e-bike batteries on the market are the Wisper Sports long range, 36V 14Wh, 504Wh capacity. With a 250 W motor that is 2 hours of discharge and about 50 km of assistance. With 2kWh of energy per kilo of coal that works out at a back of the envelope figure of 5 grams of coal per km, or about 12 grams of carbon dioxide per km of assistance. And most e-bike riders pedal too.

In NZ electricity is 68% hydro, geothermal and wind, and the rest is mostly gas (with waste steam used by the dairying industry). So for me it is probably closer to 4 grams of CO2 per km ridden on my e-bike, and my car is closer to 200 grams of CO2 per km. Or my e-bike is 50 times more efficient, it weighs about 50 times less, and doesn't contribute to traffic congestion.

Electric cars may not stack up environmentally (although there would be less particulates in the actual places where people live), but if you get someone out of a car and onto an e-bike that's pretty darn good. They'll be emitting only 4% (in my case) of the CO2 they were before, and they'll be demanding better bike infrastructure too. Out of my bike, my e-bike and my car, I'd rather get wherever I need to go on my e-bike.

David Hembrow said...

Brent: You're arguing about how many grams it might be within a small range of figures. The figure you've given shows no improvement over a perfectly average petrol car. I'm afraid that to me, this does not represent progress.

Erik: You're misunderstanding what is meant by the ~10000 figure for conversion between kWh and BTUs. This is the equivalent coal figure for power stations, also included in the link to wikipedia which you supplied. I'd already allowed for the inefficiency in burning coal in the figures which I used so the roughly 3400 figure is correct.

High speed rail uses considerably more energy than lower speed trains. How could it be otherwise ? Aerodynamic drag increases with the square of the speed. There is a reason why the motors on the record breaking TGV had to be uprated to 19.6 MW in place of the usual 9.3 MW. These are enormous and powerful motors, consuming vast amounts of electricity.

In comparison with aircraft, you're right that the trains are longer and thinner, which perhaps helps. However, they are also operating in much thicker air than an aircraft, and that has a huge effect on the energy consumption at speed.

David Hembrow said...

Matt: You never get back out of a battery all of the energy that you put in. In the case of NiMH batteries, in ideal conditions you can only get back 2/3rds of the energy. The rest disappears as heat (I don't have the figures for Lithium cells, I'm afraid, but you won't get near 100% with those either). Ideal conditions are probably not the conditions in which most people charge their batteries. It's reasonable to assume 50% in real life.

So you'll use about 1 kWh to charge your battery. In coal equivalent, that's a bit more than half a kg of coal, which you suggest will transport you for 50 km. You suggest that my figures are out by a factor of about 2.5. This may well be, for particular users and different bikes. However, the energy consumption is still high for what you get. It makes your bike's energy usage roughly comparable with a car with four or five people in it instead of roughly comparable with a car with two people in it.

It's really not that impressive.

You're right to say that NZ's generation of renewable energy is high by the standards of other countries. In itself, this is rather a good thing.

However, it's not 100% good. There was a lot of controversy over the dams, which cause quite a lot of environmental problems in themselves, and the percentage of electricity from hydro sources has actually decreased over the last few years, apparently in preference for burning more coal and gas.

Brent said...

"You're arguing about how many grams it might be within a small range of figures."

I'm not sure I understand. Isn't 142 grams per mile (electric) about a 70 percent reduction over 465 grams per mile (petrol)? That reduction seems significant and remarkable.

The guy at the link below figures driving his electric Tesla Roadster is about as carbon efficient as riding his bicycle:

Erik Sandblom said...

David, high-speed trains make fewer stops than slower trains. Actually commuter trains are the most energy-intensive because they stop once every 4-5 minutes. Fast trains only stop once every 30-60 minutes. Trains weigh about 500 to 1000 kilos per seat, so all that stopping and starting costs a lot of energy.

A TGV Duplex draws 0,047 kWh/pkm at the pantograph between Paris and Lyon at 70% occupancy (they have 545 seats).

Estimating Emissions from Railway Traffic page 74

There are additional inefficiencies, among them conversion to the right kind of electricity in the catenary. In Sweden, all trains draw 0,130 kwh/pkm. However, the long-distance trains operated by SJ only draw 0,08 kwh/pkm. Though SJ's trains are faster (200 km/h), they make fewer stops and the flexible prices result in higher average occupancy.

Here are my calculations (in Swedish)
Med hopfällbar elcykel till Gotland

The numbers show how much power the railway buys from the power company. They do not take into account how the power company generates the power.

Taliesin said...

We live in an age of hyper-mobility, at least in the developed world. This hyper-mobility is completely dependant on plentiful high quality energy sources such as petrol.

No conceivable system of transport can deliver the same hyper-mobility as the car dominated one we live in while using less energy. Delivering the same service we can currently get from the petrol car using public transport or electric cars is not going to use much less energy.

Bicycles are more environmentally friendly than any other form of transport (excluding walking) because they force us to work within the power output (and reasonable daily energy use) of the human body.

Even if we grant that electric cars will be charged using largely renuable energy (a big if), that energy still comes with a significant opportunity cost. The labour and materials needed build wind turbines or hydro-electric dams could have been used in insulating homes, building public transport systems or cycle paths.

Michael D said...

Your argument that buses are no better than cars has much more to do with the social service role of transit in car-oriented places, than with anything general about buses. Human Transit has a post explaining this.

christhebull said...

The weird thing is that in major cities, all this energy in petrol is being used to move £50,000 Range Rovers around at roughly the same average speed as a £50 bicycle off eBay.

Surely the automobile age was about cruising around at highway speeds, rather than being in a traffic jam with bikes filtering past you while you are still using all that petrol to go nowhere, the automotive equivalent of a dinosaur running on the spot? [To that effect, coach and taxi drivers are awful for leaving their engines idling...]

I like trains though. They never cut me up or overtake stupidly. Also, I can do some reading or other pursuits and I can take my bike with me. I think the cleaner image with electric trains might be something to do with the indirect nature of the emissions as opposed to the direct emissions of steam engines...

David Hembrow said...

More replies overnight.

Brent: Electric bikes being comparable with full cars for efficiency is only "remarkable" if we think the efficiency of cars is also remarkable. I don't think it is.

The Tesla guy is being rather silly in order to make an amusing point. I'm sure he eats on days that he drives as well as on days that he cycles.

Erik: Thanks for those figures. I've seen figures somewhere which suggested that he most efficient trains in the UK are the London commuter trains. These are slow speed trains, which invariably are packed well beyond their seating capacity. They stop a lot, but they still have a good opportunity to be efficient.

The TGV figures are, as you point out, incomplete. However, if you're Swedish figures are correct then the best trains in Sweden, which run most full, manage about 10 times the efficiency of an average car with single occupancy. That's about 2.5x the efficiency of an average car with four people in it. Compare with a Prius and you're struggling to find much of a difference. That's about as good as it gets for trains, and similar to figures I've seen before. It's still a lot of energy and they don't actually use it as efficiently as their promoters would have us believe. We're somehow supposed to be amazed because a packed train manages an efficiency only a bit better than a packed car.

The other problem with high speed trains (and motorways) is of course that they encourage long distance travel. People live further from their place of work and travel back and forth long distances every day. This is a problem by any motorised means.

Taliesin: I'm pretty much in agreement with you.

Michael D: The social service of local buses is much overstated. Motorised vehicles, which include buses, combined with unfriendly street design work to reduce the independence of many people by making the streets into places where they don't want to be.

kdt said...

I'm not going to join in the argument over the fine points of the statistics you cite - I think the post does an excellent job of making the much broader point that there is no form of transport that comes close to the efficiency of the human-powered bike.

That said, I do see the value of electric 'helper' motors for cargo bikes, particularly ones used to haul children in areas with hills. Making these available is likely to get more people who would otherwise be driving to use bikes, and will encourage those passenger-children to then do the same when they're older. That's me trading efficiency for advocacy, I suppose.

David Hembrow said...

kdt: You make a good point. I think there are actually quite a lot of instances where electric motors on bikes can make some sense, despite the inefficiencies.

They certainly have a part to play in helping people with disabilities to lead a normal life and cycle like everyone else does.

One of my daughters has a friend with a disability who has an electric assist bike. This is wonderful as without it she may not be able to cycle to school with the other children from her village, or go on trips with friends, for instance.

However, for averagely fit people they're simply not needed.

Erik Sandblom said...

Taliesin, we are not as hyper-mobile as you might think. The CTC says that two thirds of car trips in the UK are shorter than 5 miles. In Sweden, half are shorter than 5 km and half the population lives within 5 km of work, while two thirds live within 10 km. In the USA, half live within 5 miles of work. Clearly, many of these journeys can easily be done by bicycle.

De flesta rör sig inom tio kilometer - Ecoprofile

David, you're right that a car with four occupants can be about as energy-efficient as a train. However, cars are not typically used like that. In Sweden, half the car-miles driven are with a single driver. 84% of miles driven are with one or two occupants. I believe the average car occupancy in the UK is 1,6, so conditions are similar.

joshuadf said...

David, capital post that I will use as a reference. I think you should also do a followup on the mobility *advantages* of biking vs the low-carbon alternative of walking, which prior to about 1900 was by far the dominant mode of transport. Certainly a bike allows one more options of where to live, work, and shop, even if it's less than a car or train.

Brent said...

"Electric bikes being comparable with full cars for efficiency..."

I don't recall making that comparison. I thought I was comparing petrol cars and electric cars, with the petrol one having about three times the carbon emissions.

"The Tesla guy is being rather silly in order to make an amusing point."

Yes, I agree. But try as I might, I've found it hard to argue too much with his math. He makes the assumption that one has to eat more to cycle, and that this extra eating produces more carbon than simply driving. I realize that you reached the opposite conclusion, that people don't eat more when they cycle, but I have a hard time buying into that. More than one person has told me they cycle so they don't have to watch their diet. Racing cyclists, who live at the margin, consume huge quantities of food. The Tour de France is a carbon nightmare even without all the helicopters and cars following the peloton -- we could pack all those riders into a few buses and get them 175 km down the road for a fraction of the carbon they generate by eating.

I share your goal of getting more people on their bicycles, but I'm not really sure it will solve our carbon problems. As more than one person has pointed out, it's nearly impossible to be carbon neutral until we're dead:

Michael D said...

David, I'm not a fan of the "buses as social service" perspective. My point is that if you want transportation with a much lower footprint than the private automobile, buses (and trains) can do it. It requires focusing on transit along high-density corridors separated from traffic, and allowing/encouraging that high density to spring up around the transit. I think this has to go hand-in-hand with a focus on pedestrian and cycling infrastructure.

Electricity, I should add, can be generated from other sources -- and without a huge impact on the total cost of transit systems. Calgary's light rail runs entirely on wind power. If laws required that electricity costs reflected the externalities of generation, you'd see a pretty rapid shift away from coal.

One last point that I don't think has been touched upon is embodied energy. Bikes, cars, trains, and infrastructure of all kinds take energy and resources to construct, and in the case of cars, this amount can be quite comparable to the "operating" energy over the lifespan.

David Hembrow said...

Brent: The comparison with CO2 emissions will always depend on where your electricity comes from. Obviously it will be lower in places like France where nuclear dominates, or in New Zealand where hydro electric power dominates.

However, as coal stations are amongst the cheapest and fastest that can be built (the only real competitor in these terms being gas, which is also a fossil fuel), a rapid rise in energy requirements due to electric cars will result in the extra energy needed being likely to come from these less clean sources.

Not everyone is, or wants to be, a racing cyclist.

The human body requires a level of exercise to remain healthy. Not exercising is a major health risk. One way of achieving a reasonable level of exercise is to ride a bike for normal utility purposes. Nothing extreme is needed. It certainly makes a lot more sense than driving to a gym in order to take exercise (a point that the Tesla guy himself also makes at the end of his post).

While racing cyclists eat well, they don't overdo it. There are plenty of non cyclists who eat rather more than they do, even when you don't include the extreme types.

I do race a bit myself. Back in June, I took part in a six hour race, covering 235 km in that time. My effort came to the equivalent of around 3700 calories more than usual for that day (there's a calculator here).

I'm vegan, so somewhat more efficient than average.

The link suggests that I consumed about an extra 4.2 kWh over the six hours. That's about 0.01 kWh per km at the fastest, and therefore least efficient, speed I can sustain over six hours. That's quite a lot less than the amount that the Tesla chap reckons he consumes when cycling at a much lower speed.

I still don't think the figures are coming out as remotely comparable, even when leaning on "clean" sources of electricity.

David Hembrow said...

Michael: You say that "Calgary's light rail runs entirely on wind power."

I'm afraid that is also a bit of a nonsense. It's a greenwash statement. I have no figures for this light rail system, but if it's not making particularly good use of the energy produced by wind power it would be better for that energy to be used for something else - and the more polluting source used currently by "something else" to be turned down a notch.

The problem with having a "much lower footprint" is that typically we're still talking about using all of the same energy over just a slightly longer period of time. PT is not particularly frugal. If we accept that fossil fuels are running low, and we want to do something about this problem, then a few % points difference, or even a doubling in efficiency is actually no big deal. You're talking about making the resource last maybe another decade, not for another thousand years. I'd rather like to leave some of this stuff for my great great grand-children, and their descendants to use.

I agree with you on the other points, though. In particular embedded energy, which is often forgotten. The embedded energy of electric vehicles is large, particularly due to the batteries which themselves have a short life-span. A lifespan of 500 charges, or 5 years (even if not used at all), is quite good for Lithium rechargeables.

Erik Sandblom said...

David and Michael, I don't think it's nonsense to say that Calgary's light rail runs completely on wind power. I'm assuming that's what they pay the power company to deliver. Other clients pay them for coal power, but that's up to them.

It's just like when I buy ecological vegetables at the grocery store. The same store sells "bad" vegetables and meat to other customers, so in a sense I'm contributing to that, but the fact is that I'm not paying for what I don't buy.

At the end of the day, comparing bicycling to public transportation is interesting but perhaps a side track from effective bicycle advocacy. Many people who cycle find public transport to be a reassuring backup.

Matt said...

""The Tesla guy is being rather silly in order to make an amusing point."

Yes, I agree. But try as I might, I've found it hard to argue too much with his math."

There's at least one glaring omission in his maths: the fact that he completely fails to take into account the carbon balance of growing and transporting the food which the cyclist consumes. Like the fuel mix used to generate the electricity, this will vary widely from cyclist to cyclist.

Here, David JC MacKay claims that for a typical diet, walking uses 1/4 as much energy overall than driving a normal car. Here is the claim that cycling is 3 times as efficient as walking, which would make cycling twelve times as efficient as driving. From these claims, unless an electric car is twelve times more efficient than a petrol car (I think not), it's better to cycle.

Michael D said...

"...if it's not making particularly good use of the energy produced by wind power it would be better for that energy to be used for something else..."

The vast majority of electricity in Alberta is generated from coal and gas. If the C-Train weren't buying wind power, that wind power would not be redirected anywhere else -- as someone has to pay for the increased cost relative to fossil fuels. It's important to note here that the C-Train generates more in fares than Calgary spends on light rail operating costs, which should render arguments regarding public subsidies moot.

The point isn't so much about Calgary, but that in practice you can have transit (e.g. light rail or trolleybuses) that relies little on fossil fuels, and which will be able to withstand a shift to a world with scarce fossil fuel.

Anonymous said...

Hi David,

Great number crunching - I enjoy these posts, thank you. It is hard to know where to stop when comparing the energy consumption of a human but ultimately all of this comes down to two things: there are too many of us and, we (in the 'first' world) consume too much.

I have an e-assist bicycle (a dutch model) with a 252Wh Li-ion battery and 250W motor. With this and me pushing hard up my hilly 22km (quite a few 10% gradients) commute, I can average 25km/h. It cannot be used as a 'moped' which is a good thing IMO.

This battery lasts me for about 80km over our hilly terrain. In the hot, humid summers here it really helps a lot (I might not be disabled but on some summer days I feel like I am...). I can see how it is completely unnecessary in the NL for someone like me.

Assuming that I actually use 350Wh to charge the battery (I really must measure this), this means I produce 200g of CO2(e) for that 70km journey assuming electricty is ALL from coal, which is likely here. Our electricity is 100% 'green' - at least that's what we pay for - (that could just mean the 'promise' to plant a tree... who knows?) so supposedly the emissions are zero, but that is clearly nonsense. I hope to generate this power from solar alone soon.

If I assume that the electricity is 100% from coal, I produce about 3g CO2(e) per km on my e-assist bicycle.

My very efficent, small, EU made car produces 130g CO2(e) per km.

Of course, I'm planning on changing my commuting machine so that what I lose on the hills I can gain on the flat bits...although I suspect I'm going to have to increase my baked bean intake somewhat...

Paul Martin
Brisbane, Australia

Brent said...

"From these claims, unless an electric car is twelve times more efficient than a petrol car (I think not), it's better to cycle."

I'm not sure this claim controls for speed. If I have my math right here, the Roadster traveling around 20 mph (30 kph) would use about 9 kWh per 100 km*, while a 90 kg cyclist would use roughly 10 kWh per 100km.



One incidental observation: in California, the largest users of electricity are the various oil refineries (or maybe the second largest). I've been dying to know how much electricity is used to produce one gallon (or liter) of petrol, and posed the question many times on message boards. The answers vary from 3 kWh to 14 kWh per gallon (about 1 - 3 kWh per liter). Recently, Nissan started using the number of 7.5 kWh** per gallon, which I guess is as good as any. If Nissan is right, you would be able to drive an electric car (at 160 wH/km) some 47 km on the electricity used just in the production of about 4 liters of petrol. To put it another way, petrol pollutes hugely at least twice: once in its refining and once in its burning. And this ignores the carbon costs of extracting, shipping, pumping, transporting, etc.


David Hembrow said...

Brent: Your figures are not believable. My ride of 235 km, so fast as possible, consumed an extra 3700 calories, which is approximately equal to 4kWh. This is much less than Tesla like to claim for power consumption of a human.

But it's not only Tesla themselves, Evnut also appears to be less than an impartial source of information. While they're concerned about the additional costs of producing petrol they seem not to be concerned about the additional costs of producing electricity.

A significant proportion of electricity produced by a power station is used inside the power station. Something has to run cooling pumps, control/safety systems, regulators etc. Quite a lot of energy is inevitably lost in distribution, especially if power stations are located far from where the electricity is used.

It's a similar story with any energy source. There are always costs. Power stations have to be built, emissions from construction are enormous. Uranium, coal, iron and copper (amongst other things) need to be mined, refined and made into components or fuel for power stations. Silicon solar cells have considerable embedded energy. Fibreglass for wind turbines also has an impact. All the components and fuels need transporting.

There is no method of generating electricity which doesn't have external costs. If you're going to count them for one source you really ought to count them for all sources.

Slow Factory said...

David: Under EU regulations, pedelecs (most electric-assist bikes) have assistance only to 25km/h, but can still go faster unassisted. It would follow that the same cyclist could go farther and/or faster on a pedelec than a normal like. Of course aerodynamic enhancements such as the ones you champion can help, too!

Also reducing this argument to CO2 plays right into the hands of those who want to, e.g. power private urban electric automobiles with wind, tidal, solar or micro-hydro.

David Hembrow said...

Green Idea Factory: One of the many problems with electric bikes is that above 25 km/h you're carting around a load of weight which does nothing useful at all, but does take energy from the rider. There are also transmission losses due to the motor coupling either to a wheel or the drive-chain. As a result, electric bikes are inevitably less efficient, which makes them slower with a shorter range than non-assisted bikes.

They also have a much shorter lifespan due to the short life of batteries. Even the manufacturers only claim around 500 charges are possible. That's really not much for a bike used on a daily basis (and it'll be reduced by various factors such as by charging in the cold). The shelf life of such a battery is only around 5 years even if it's not used, so there's no point even in buying a spare to keep your bike going after the manufacturer discontinues the battery.

Compared with normal bikes, they have a very much shorter lifespan and/or will require a lot of extra expensive work (on a five or ten year old bike?) in order to keep running.

Quite honestly, they're mostly not very nice bikes, either... (yes, that's opinion, not fact).

This is why while they're great for those who really need them (disabilities, perhaps old age etc.), they're really rather a bad idea for those who really don't need them.

I agree with you about reducing the argument to CO2. It clouds the real issue, which is that motorised transport consumes vasts amounts of energy in an inefficient manner. We should not waste energy, wherever it comes from. All energy has a cost, even "clean" energy, of which we have a limited supply.

If the cleaner energy is all used to charge electric vehicles then it simply means that dirtier energy has to be used for other purposes. We can only use each kWh generated (equivalent to a whole day of physical work) once.

Jon Bendtsen said...

@David: Bikes without electric motors are quicker than those with them (which are limited to 25 km/h).

Please elaborate on why you think this statement holds true, because in my knowledge electric assist bikes only stops the engine at 25 km/t, you can still pedal faster.

I met one yesterday which not only did that, but also, at 30 km/t started recharging the battery which was lovely downhill because then he did not get into dangerous descent speeds.

Brent said...

"Your figures are not believable."

For the 9 kWh / 100 km at 30 kph figure, I'm relying on published numbers from Tesla. The figures may be unbelievable, but I haven't yet found any credible evidence to disprove them, despite some considerable efforts on a few blogs I read.

Similarly, I used to illustrate the Nissan number 7.5 kWh to refine a gallon, but one can find the same number from other sources, including Nissan themselves. But you're right to point out that there is some doubt about that number. I started a thread some years ago on a Tesla-related site. The community there has yet to find a reliable number:

David Hembrow said...

Jon: It's quite simple. Extra weight costs energy to transport it. This especially applies every time you need to accelerate or climb a hill, but also on the flat. Electric assist adds weight. What's more, there is a mechanical coupling between the electric drive and the bicycle. When not in use this will still inevitably cause some drag. I've not measured it, but wheels with electric motors in them feel a lot like those with hub dynamos. They don't spin as freely as a normal hub (moving the motor to the drivechain changes but doesn't avoid this problem).

David Hembrow said...

Brent: This is getting repetitive and I think it's time for Occam's Razor.

The promoters of electric (and non-electric) cars rely somewhat on a smoke-screen which makes it difficult to find reliable figures, and on the public's lack of understanding of these figures.

It is not in the interest of Tesla to be a particularly good source for accurate information about cycling.

The company simultaneously boasts about the availability of "288 horsepower" which equates to over 400 kW, or the equivalent power of around four thousand average cyclists, while trying to talk you into thinking that they offer an energy efficient form of transport.

It's quite simple. To move the small mass of a bicycle at low speed simply takes a lot less energy than to move the much larger mass of a car at typical car speeds.

Cars are not designed to be remotely as efficient as bicycles are. You can do a very simple experiment to prove this to yourself. Simply try pushing a car vs. pushing a bicycle (even an electric bicycle). Is it realistic to believe that the car travels on an equivalent amount of energy to that generated by a human sitting on a bicycle ?

It would be truly extraordinary if it were true that it took less energy to drive a car than to ride a bike. And indeed, this is not the case, no matter how many people try how hard to cloud the issue. I'm afraid I've got work to get on with and simply don't have time to read many different implausible ideas from around the web and try to discredit them.

The figures I presented in the original post are reasonably accurate.

Slow Factory said...

David: Thanks. About the 25km/h speed thing, I actually think most commuter or utility cycling is done at less than that speed, and up to that speed a (charged!) pedelec is easier to pedal. If you have a tailwind your bike will get boosted or directly (as opposed to with an intermediary like a windfarm!).

I have lived in very hilly places such as Prague, San Francisco or Washington D.C. Granny gears reach their limit, though it was very rare that I ever dismounted. A bike which gets you over some steep obstacles is great, and I think some of the time I would not any assist. Also there is the sweat factor when it's hot, and I would be curious to see an energy comparison of an electric bike assist vs. taking a hot shower. (To make things clear, I also lived in NYC and never wanted electric assist even in the nasty summers. It's very flat).

I cannot argue against your battery-lifetime comments, but while pedelecs are much more complicated than normal bikes, companies like Bosch and Shimano have introduced their first solutions for pedelecs, and this should mean that stuff will be more robust (and these companies are in no danger of disappearing).

My issue about "green energy" is that if a vehicle is powered this way it still has all the other problems and external costs, especially if it is a private, urban vehicle.

Neil said...

I agree that electric cars still have all the car-head and anti-community problems that petrol cars do. But surely it's better to have electric assist cycles (not electric mopeds) if that will persuade people to cycle who are otherwise put off by the distance or hills.

I think your point (as always) is that good infrastructure is cheaper and better way to achieve most of this. and I think our struggle (as always) is to understand how that can be achieved (technically and politically) outside NL.

BTW - 25km/h is the top assisted speed (for those that conform), you could cycle faster yourself, just the assist should switch off at that speed.

Jon Bendtsen said...

Okay, so you might get a lower top speed, but I think adding electric assist will also make the average speed higher.

It might not be as efficient, but you talked about quicker, not efficient.

Slow Factory said...

I think it is important that pedelecs are targeted at people/families who are in the market for a second or first private car, for those times when going long distance cannot be done easily with a bodylec* in combination with the train, or when there is no time and when any kind of car (even a shared one) is overkill.

Cargo bikes with a box have a limited market outside of flat places... if I lived in a hilly place and had kids I know what I would do.

We need to make people clear about the continuing externalities of electric automobiles (and tax them), and we ought to put pressure on pedelec makers to have very long warranties on components which cannot be fixed on the side of the road in Afghanistan (no disrespect intended towards the wonderful South Asian cycling culture).

*Body electricity pedal bicycle

Anonymous said...

Plenty of responses on this topic and I am not going to guess which is the right answer but I agree 53 euros is cheap for the amount of energy you buy. There are some good discussion papers available on the energy needed to produce food but few comparing the eating habits of cyclists and car drivers and bus or train passengers. I estimate my ride to work needs 800 calories so I expect to eat more than a car driver but perhaps I eat better food? It may be possible to watch the food consumption figures for China during the shift from a nation of cyclists to a nation of drivers. The time and effort saving mind set from the car culture may be mirrored in the adoption of junk food.
For fun I’d like to say that a cyclist doing the weekly shopping won’t overload those panniers with bottles of water from France and is less likely to waste food, having both a good appetite and some understanding of the energy needed to get some more.
We might like to consider the impact of the recent BP oil spill along with the ongoing mess in Nigeria against the diffuse yet real damage we cause by throwing out food that we don’t eat. Do car drivers create more waste?
Mark Garrett, Bristol UK

greenobike said...

I take from your discussion that all powered transport is resource inefficient. There is little point in any effort to make slightly more efficient vehicles. The goal should be to make less resource intensive sources of energy. Essentially, fossil fuels must be abandoned in favor of renewables. I highly recommend the film "Fuel."

And I agree about the recent BP disaster. All oil companies put profits ahead of any ethical behavior to an obscene extreme. Remember what Dutch Royal Shell did to Ken Saro-Wiwa.

kfg said...

Tesla is playing little math games, specifically treating the human body as if it were a simple machine, with a simple energy in/energy out function, and perhaps even one that can be turned off like a car.

And it ain't. It's a biological process that, like the coal furnace, operates 24/7 and LOAD BALANCES to maintain efficiency.

Yes, it's true that when I'm racing and training and have 5% body fat I may consume several thousand calories a day . . . AND sleep for twelve hours to conserve energy as well.

However, when I am not racing or training and have 10% body fat I assure you, if I spend a week riding to the shop for every meal and the next week having food delivered my food consumption does not vary. Not by one bite (racers get in the habit of monitoring their fuel just like Grand Prix auto racing teams do).

The fact of the matter is that most of us, who are not anywhere near pushing the limits, consume energy rather in excess of our actual needs; because we want to. We then find ways, usually insensible, of frittering them away until the load is balanced. If we should, for some reason, run a bit on the other side of the razor's edge, we find ways, again usually insensible, of slowing down a bit, maybe sleeping an extra 10 minutes and getting up off the couch a few times less . . . until the load is balanced.

We eat what we eat and the very tiny amounts of energy, because cycling is so efficient, that are expended in simple utility trips just go into the frittering away budget. People who take up utility cycling to loose weight are usually disappointed, even if they carefully control their diet in a LOWERED calorie state.

It isn't burning petroleum that is going to doom the planet; it is efficiency engineers who believe it would be a good thing to apply their "science" to the human metabolism and who think, for some strange reason, that it can actually be done that are going to doom humanity.

And when they plug you into the real matrix they won't feed you pictures of pretty women in red - that would be pointlessly inefficient.

dothebart said...

from my last cycling holiday in mallorca I can truly tell you that cyclists _DO_ eat more. I'd say at least twice as much.

David Hembrow said...

A "holiday in Mallorca" is by definition not a normal day. Probably these cyclists were doing more than they usually do, and in any case, people often eat more on holiday.

It being nearly Christmas now, we can expect that in the next few weeks a lot of people will over-indulge without taking any exercise at all.

dothebart said...

heh, yes. My daily commute is either 30 or 40 km whether I shortcut one way with the tram or not.
On Mallorca its been between 80 and 150 km with different elevations.

I just wanted to point out that it _does_ make a difference whether you go by bike or not how much hunger you get -> eat.

I've got no problems with that, since I like eating ;-)

I think its a perfect workout for an office job.

But if you sum up the numbers of everything else precisely, you should be accurate here too. I rather enjoy eating something tasty then draining my money into a car.

btw, i've read some numbers where they sum up, if you ate some beef from argentinia, _your_ carbon footprint to walk the 5 km to the shops instead to use a car is higher!

Erik Sandblom said...

dothebart, most people do not commute 30 km. In the USA, 50% of the working population commutes five miles (8km) or less to work.

In Sweden, two thirds of the population lives within 10 km of work.

De flesta rör sig inom tio kilometer - Ecoprofile

sundraparipooranan said...

Most fuels we are talking fossil fuels that have taken millions of year to form from the dead plants and animals under the pressure exerted deep inside the earth. So this blog is very useful to all to save our country thank you for posting.
Save fuel, Save Water, Save Electricity, Save Environment, Saving fuel, Fuel, Water, Electricity, Environment.

Unknown said...

So, the oil rig gets the oil up emission free, the oil is transported emission free, the oil is refined to petrol emission free, the petrol is transported emission free ??


David Hembrow said...

Simon, I agree. Note also that coal has precisely the same problems as you mention.

Unknown said...

You should update your article and use proper CO2 emission data from electric grids. Its quite misleading what you write.
See for data for example here:

E.g. the emissions in the OECD countries are about 404 gram per kWh electricity.
This is way better than any combustion engine!

David Hembrow said...

Unknown: The data is a worthy addition. Thank you. However note this part of the summary from your link: "Using EVs, in EU, saves on average 50–60% of GHG emissions compared to internal combustion engines." i.e. an EV could perhaps half the GHG emissions per km driven.

For now I'll ignore the problem of sudden growth in consumption which could force electricity generation to switch to less green means of production (especially for charging overnight on windless nights). Reducing output by 50% per km driven sounds really impressive, but it's hardly worth anything at all in practice. Why ? Because the growth in use of cars continues apace. Even if all cars overnight were converted to electric power and produced half the emissions, that would only return us to the already far from sustainable level of output which we had a few years ago. In the case of the Netherlands it would return GHG output from cars to the point that had already been reached in the 1980s, and growth in usage would then continue from that level once again.

That drop is only visible by means of a thought experiment in which all cars are swapped overnight. It won't be seen in reality because the stock of cars won't be replaced overnight but gradually over decades. All that EVs can then hope to achieve is a temporary slight reduction in the steepness of the slope of the steadily increasing GHG output due to motor vehicles.

i.e. EVs are not a real solution to the problem of GHG output. Travelling much less by motorized means is a solution.

(hint: if you wish to reply please use your name as I don't generally publish anonymous comments)