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Other articles have compared the energy costs of biking to driving, when we consider the energy needed to produce the cyclist's food. (source) This post is different. Here I'll look only at the *cost* of the food, and compare that to the cost of gas. I'll also use those figures to figure the "MPG" of a bicycle, if we use our gas money to buy food to fuel our biking instead.
A 155-lb. person biking with moderate effort (12-14mph) burns about 596 calories an hour. source Driving takes about 68 calories an hour (source), so our cyclist burns 528 calories an hour extra by biking instead of driving.
I'm rounding the speed down to 10.18 mph to account for stop signs and traffic lights.
The average car gets 20.36 mpg.
So, conveniently, it takes a cyclist 2 hours to go the distance that a car would go on a gallon of gas. The cyclist will thus need 2 x 528 = 1056 calories to do so.
What is the cost of 1056 calories? Of course it depends on the food:
"Price per gallon" of biking (i.e., Cost of food to bike the same distance that a gallon of gas would take a car)
$8.94 salmon or catfish (farmed)
$6.56 Big Mac
$4.21 ground beef (85% lean)
$3.35 chicken breasts (boneless)
$2.88 cheese
$2.04 Cheerios
$1.17 potatoes
$0.79 peanut butter
$0.77 oats
$0.66 pinto beans
$0.58 rice (white or brown)
So that lets us compare the price of bicycle energy with the cost of gas.
We can also do a similar calculation: If we spent the same amount of money on gas that we spent on food, how far could we ride the bicycle? That is, what is the MPG of biking, if we spend the same amount on food fuel that we would have spent on gas fuel?
The average price of U.S. gas is $2.66/gallon. We can go 20.36 miles on $2.66 in the average car, how far can we go on $2.66 with a bike?
"MPG of bicycling" (i.e., miles a cyclist can travel on $2.66 worth of food)
6.1 miles - salmon or catfish (farmed)
8.3 miles - Big Mac
12.9 miles - ground beef (85% lean)
16.2 miles - chicken breasts (boneless)
18.8 miles - cheese
26.6 miles - Cheerios
46.1 miles - potatoes
68.6 miles - peanut butter
70.4 miles - oats
81.6 miles - pinto beans
94.1 miles - rice (white or brown)
So if your food fuel comes from the items in the first section, it actually costs you *more* to bike than to pay for gas.
Food for thought.
Edited on Feb. 4, 2010 to use current prices for food and gas.
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Of course, if you just go with an electric bicycle, then the cost of the electricity used to go 21 miles is around 6 cents.
(Assume 100 watts average, 33% total efficiency of motor/battery/transmission/charger, so 300 watts, 300 watts for 2 hours = 0.6 kW/hr, which is 6 cents at $0.10/kWh.)
It's not that the human body is so efficient (it's around 20% for a well trained person, which is probably comparable to an automobile engine), or food is cheap. It's that a bike uses so much less power, mostly because it goes much slower (power needed to overcome air resistance is proportional to the speed cubed) but being so much smaller and lighter certainly helps a lot too. Motorcycles get around 100 mpg -- better than a car (because they're smaller), but nowhere near as good as a bike (largely because they tend to travel at car speeds rather than bike speeds.)
Side note: A gallon of gas contains the energy of about 31,000 calories. If we could efficiently digest that, it would power your cycling for 55 hours, taking you about 700 miles.
Last edited by dougmc (2008-09-25 08:19:12)
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Anther good argument for being vegetarian! Thanks Michael, this was intriguing.
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Imagine the dollar value of replacing a gym membership (where most people are just a mouse on a wheel) with commuting by bike. Add in the value of your additional free time that is gained too.
I wish commuting by bike was easier for most people. I don't blame many people for not wanting to battle car traffic and breath in exhaust. That's why I want to help make the roads more bike-able.
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Two topical articles folks following this thread might find interesting:
http://knol.google.com/k/speed-costs-power
http://knol.google.com/k/energy-global- … c-bicycles
The former discusses the energy cost per payload curve of different vehicles (bicycles included), while the latter refines the argument (made earlier in this thread) that electric bicycles are more energy-efficient than strictly human-powered ones. One of the interesting points made is that people who get light exercise on a regular basis actually consume fewer calories than those who are sedentary (though from that point, food intake increases with quantity of exercise) -- making an electric-assist bike where the user pedals along with the motor preferable to an electric moped or an e-bike which doesn't encourage pedaling, as getting the rider enough exercise to get them out of the "sedentary" category results in less, rather than more, calories consumed.
As for the replacing-a-gym-membership argument, it's a compelling one for me -- when I commute on my unassisted bicycle, my commute is 75 minutes each way; on my e-bike, when I'm putting in the same amount of effort, that same commute takes 45 minutes one-way. 90 minutes of my day enjoying myself outdoors is easy to justify -- it's less than I'd spend driving a car both ways and then spending an hour in the gym. Spending two and a half hours of my day commuting, by contrast, is occasionally a bit hard to swallow.
BTW, that 6 cents for 21 miles figure seems rather high to me -- when set in low-powered (350W) mode and ridden with moderate effort, my e-bike easily gets 50 miles per each of the two (one hidden in the frame, one external) 20Ah 36V batteries. Each of these batteries holds about $.043 worth of electricity at current rates; if we assume that the charging mechanism is only 66% efficient (which is low -- high-cell-count batteries can be charged with 85% efficiency under optimal conditions), charging both batteries for 100 miles of range would cost $.13, or 45 miles rather than the previously quoted 12 for $.06. Granted, this is running as a human-electric hybrid, so the cost of food would need to be taken into account as well to make the comparison fair. (Pedaling makes a huge difference in range -- in low-powered mode the bike has a 2.5 hour runtime per battery, but averages only around 10-12mph on its own; the mid-drive assist makes a fast cadence easy to keep up, however, allowing one to go much faster when working in tandem with the motor. In high-powered mode, the bike will do 20mph on its own and it takes only a moderate effort to push that up to 28-29 on flat ground, but factory specification is only 50 minutes runtime per battery).
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This topic makes me come to the conclusion that the most energy efficient (and environmentally friendly) form of transportation is by electric bike.
#1 - The amount of electricity that an electric bike uses is about $0.06 per hour of travel (negligible).
#2 - A typical bicycle uses very few materials and energy to build compared to - car, bus, train, etc.
#3 - It's possible to use completely recyclable batteries.
I already knew how much more energy efficient an electric bike is. The human body is vastly inefficient at producing power and food is a very poor source of energy. Yes, an electric bike will take more power to travel at the same speed as a normal cyclist, but it's still negligible, especially considering how much more convenient it is to not pedal and work up a sweat. (or pedal lightly).
So far, electric power bicycles using lithium battery power is BY FAR the most effective use of electricity for transportation. Electric cars - not so much, they are just too heavy, and battery technology is not good enough yet. (or cheap enough).
Charles, I JUST saw you made a post above about your electric bike. I stand behind what you wrote. The gym replacement comment fits situations were people commute 5-10 miles each way. You are clearly better off using an electric assist bike for your long commute. I would do the same.
I support both forms of cycling, pedal only, and electric. Both have their pros and cons, and the best choice depends on your specific situation.
I am about to start working on my second e-bike project. Last year I built a homemade design onto a road bike, which got me up to 30mph, but didn't have any low-end torque for starts or hills. Check out http://endless-sphere.com/forums/viewfo … 0806302829 There's a whole community of people making/riding e-bikes. It's growing fast.
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> #1 - The amount of electricity that an electric bike uses is about $0.06 per hour of travel (negligible).
Well, assuming 50% efficiency for charger and motor and such, and $0.12/kW*hr cost, that's 250 watts of useful power over that hour -- more powerful than most cyclists. I suspect that $0.06/hr figure is actually on the high side ... (though you could just let your bike go faster ...)
Really, the biggest reason that bikes are so efficient is that they go slow. If you designed a compact car sized car that had a top speed of 20 mph (and much slower up hills), you could make it get two hundred mpg pretty easily. It would also be much easier to make it electric -- you'd need much smaller batteries to get the same range. The small size and weight of bikes certainly helps too, but it's mostly that low speed.
For both cars and bikes at speed on level ground, most of the power goes into overcoming air resistance, and that varies with your speed cubed. So the energy needed to overcome air resistance over a given distance is proportional to speed squared -- half the speed, you need one fourth the power.
Of course, given the choice of a 75 mph car or a 20 mph car, which would you prefer to drive? At $2.50/gallon the price is obvious, but at $15/gallon, it might not be so simple.
As for lithium power, current lithium batteries don't survive that many cycles (a few hundred when they're fully charged and discharged at a moderate rate) and cost more per kW*hr than NiMH cells. For now, I think NiMH cells would be significantly more cost effective for electric bikes, even though they would weigh somewhat more for a given amount of energy. But this could change in the future. And new innovations in fuel cells could remove the need for batteries entirely in the future, consuming gasoline or alcohol (or hydrogen, if we could find a good way to store it) just like a car, but being much more efficient about it and using that to create electricity to run a motor.
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Lithium batteries are capable of lasting considerably longer than a few hundred charge cycles if appropriately provisioned. My bike's LiCo batteries (notably not using one of the newer, longer-lived but lower-energy-density chemistries such as LiFePo4) are warrantied for 3 years / 30,000 miles, and expected to remain usable well beyond that point if well-cared-for. That said, there are several tradeoffs which went into achieving that robustness:
- The top portion of the battery's capacity is never used. The cells are capable of storing at least 4Ah more than what they hold at the voltage where the BMS cuts off any charging attempts.
- The amp drain (and charge) rate is limited. Compared to hub-motor ebikes where it's sometimes necessary to dump in more power to be able to climb that hill, the center-drive design makes it practical to require the user to downshift when they want to climb something steep. There is no regenerative braking. As both human and motor share a drivetrain, unlike a hub motor ebike, a broken chain means a long walk home if one doesn't carry a spare.
- The BMS and controller are aggressive about cutting down or shutting off battery power in overheat or other anomalous situations. Getting into overheat situations in .tx.us summers is not prohibitively hard to do. :)
- The battery is made by a US company that got started designing lithium batteries for use in the space industry (in which service calls to replace a dead battery are prohibitively expensive), and is not price-competitive with its overseas competition before taking charge-cycle lifetime into account.
I find these tradeoffs worthwhile to have a bike with a reasonable weight and peace-of-mind from not needing to deal with range anxiety. (Getting back to weight -- TX law actually requires that an electric bike weigh less than 100lb to qualify for the "bicycle" classification, and I've seen some electrified cargo trikes with lead-acid batteries that clearly wouldn't qualify here... so for folks attempting to convert a heavier frame, paying attention to battery weight may actually be obligatory).
Anyhow -- batteries are indeed getting better all the time. I'm quite certain that when these die, they'll be replaced with something lighter, cheaper, and higher capacity... my point in this post, though, is that if one is willing to make some tradeoffs, even current lithium batteries shouldn't be seen as doomed to a few-hundred-cycle lifespan.
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I think bicycling changes MANY things that reduce energy consumption.
I just successfully finished a year fulfilling a New Year's resolution made December 31, 2008. That resolution was to put more miles on my recumbent than on my car.
I think it is significant that the total miles I traveled was significantly less than before. We are talking well over 2200 miles by bike by a 62 year old commuter.
A bicycling culture reduces overall calorie consumption from all sources.
I am here to tell you that I do not feel that I was deprived during that year of attending events. There were a couple times I wanted to haul my computer and monitor to a computer club meeting, but I didn't. That' about it.
Commuters don't haul a lot of stuff. I hauled books and papers, that that was nothing with a saddle bag.
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This thread is fantastic.
I love MBJ's calculation, but I think he forgot that the driver also eats. So depending on his/her diet choice the the MPG cost might be way higher. Of course, I am not sure whether the energy costs of cooking and shopping for groceries may be counted as well.
The mere thought gave me hiccups.
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The fact that the driver also eats isn't irrelevant. Now, the fact that the driver *burns* calories by driving is indeed relevant, but I didn't think anyone would nitpick differences that amount to pennies. But since that's apparently the case, I re-did the analysis, looking at only the *extra* calories burned by bicycling (i.e., subtracting out the calories burned while driving). It doesn't make much difference.
As far as whether to account for the energy costs of cooking and shopping, no. This is a financial analysis. Unless you incur a big financial penalty somehow by shopping and cooking (beyond what you pay for the food), then cooking and shopping aren't relevant.
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Chapeau!
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As a "serious" cyclist, who still only rides about 10 hrs a week at the most, I can tell you that my grocery bill is significantly higher than it is when I don't ride. I just walk into my apt with 60lbs of groceries in my hands. Cycling does not encourage reduced energy consumption when it comes to food.
Doug, I agree with you on the reason why bikes are so efficient. The lower speeds definitely are a big factor. Although you can't argue with the 98% efficiency of a bike drivetrain too. Yes, most people haven't a clue about how much more energy expensive it is to travel at high speeds.
I've been commuting on my electric modified mtn bike lately. It's fun since I'm only 2 miles from work and most stores. No parking or traffic stress. It has a 450watt motor (I average about 250watts over the course of a trip.)
Oh, I was thinking about how many hidden costs there are to cycling for commuting (pedal power).
- The hot water for my additional shower (bc I get sweaty when cycling) costs more to heat than my electric bike costs to charge. In fact, it costs more money to cook 2 servings of pasta on the stove - than to charge my ebike for 12 miles.
- The additional cost of laundry is 5 times as much as the electricity to charge my bike for 20 miles. ($.25 for each set of bike clothes (5 sets of bike clothes for each load at $1.25)).
Bottom line, in my opinion, is if you can spare the addition 200-$300 for a basic electric bike, it is more than worth for commuting. The number one reason to ebike instead of pedal is so you don't get to work sweaty and have to spend all that time changing and what not.
A normal bike is good for trips that are <1 flat mile, that's about it. (Unless you have weight loss goals, or no other time to exercise).
Last edited by rich00 (2010-04-16 00:30:41)
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Have you heard of John Robbins? He was heir to the Baskin-Robbins empire but walked away from it because of the health issue he had growing up eating ice cream three meals a day. Or so he says.
Anyway, in one of his books he makes the claim if your car gets better than 30 mpg you're actually better off driving if you're a meat eater. It take so much energy to produce meat it would take more energy to feed your additional calorie demands than if you just drove everywhere.
I'm not saying this is true. Yes, I do eat meat. Not interested in starting a food debate. ;-)
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Electric bikes are a neat stop-gap solution to lower reliance on automobiles, and they are likely more efficient than other things we take for granted like refrigerators and water heating. However, I respectfully disagree with the contention that normal human-powered bikes are only good for trips less than 1 flat mile.
A pedestrian can walk at around 3 miles per hour, more or less, without breaking into a sweat or feeling uncomfortable. In fact, it's really pleasant to walk at a relaxed pace, without feeling rushed, without pushing your body or your heart rate very high. That same level of activity can comfortably propel a bicycle along at a rate at least double walking speed. Sure, other cyclists may pass you and secretly think you're some sort of noodle-legged weanie, but you'll get where you're going without looking like you stepped out of a sauna.
The problem with cars is not just that they use energy and emit noxious gases. They create an inhospitable landscape and marginalize non-motorized road users like cyclists and pedestrians. Driving an e-bike doesn't put you in the same class as the Humvee driver on I-35, but it's closer to driving than walking, and more appropriate for longer distances or special needs.
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Ugh, I hate to hear people using electric bikes for a 2-mile commute. 2 miles? you could walk and get there in 30 minutes tops. The electricity takes away any exercise you'd get, plus if you do exercise, you'd be doing it after work. Time wasted. If you just sit at your desk for 30 minutes the sweat goes away, and you are not smelly. I can tell you from experience. I've never used the shower at work. Electric bikes also use batteries which are not biodegradable. There's also the maintenance. I could go on, but I won't.
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I once thought about buying a motorscooter. I then realized how pointless it was. I couldn't go much faster on one than I can cycling. I have to have insurance, registration, gas, maintenance, etc. It wouldn't extend my range at all. It's not like I'm going to ride up on I-35 to Dallas any more than I would ride my bicycle. So why bother? I'm sticking with my bicycle.
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Ugh, I hate to hear people using electric bikes for a 2-mile commute. 2 miles? you could walk and get there in 30 minutes tops. The electricity takes away any exercise you'd get, plus if you do exercise, you'd be doing it after work. Time wasted. If you just sit at your desk for 30 minutes the sweat goes away, and you are not smelly. I can tell you from experience. I've never used the shower at work. Electric bikes also use batteries which are not biodegradable. There's also the maintenance. I could go on, but I won't.
For a 2-mile commute you're entirely right that an e-bike is not the right tool for the job, but I strongly disagree with the arguments you make in support of that premise.
Lead-acid batteries have serious pollution issues -- but newer chemistries (which are used in almost all e-bikes sold in the US) generally don't share them. Moreover, the argument has been made that the energy involved in creating and shipping the batteries is more than made up for by the energy that goes into food production for the extra calories burned by a rider eating a conventional diet. (This actually doesn't work for folks who don't pedal or otherwise get no exercise at all -- sedentary people consume more calories than those who get light exercise, though from light to moderate and then heavy exercise the caloric consumption curve goes up like you'd expect). Not sure where you're going re "maintenance"; a brushless electric motor is pretty much maintenance-free. I've had much more downtime due to conventional bike parts failing than trouble from trouble from the electric systems.
The electricity most certainly doesn't "take away any exercise you'd get" as long as you're still pedaling as hard as you usually would -- if you are, all it does is make you faster; thus, you're burning fewer calories per unit distance, but the same calories per unit time. I can't afford to spend 2.5 hours on my bike every day, which is what it takes if I commute both ways without taking the bus partway and without electric assist. (The bus doesn't make my commute any shorter than cycling unassisted in terms of time to get from A to B, but it does mean I can be working from a laptop or reading part of the time; that said, I'm much faster on the e-bike than taking a bus). Granted, my commute is not 2 miles each way.
Anyhow -- I have test results from my doctor showing that the benefits of exercise from daily e-biking (using a mid-drive bike built to be pedaled rather than one of the hub-motor designs) is very real and substantial. The misperception that someone riding an e-bike can't be getting any exercise is something I find myself needing to spend a fair bit of time fighting (one doubting coworker had to pull up behind me in his car and see how hard I was pedaling to believe; another got the point when I came into the office without showering first), and I don't appreciate folks working to spread it further.
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plarson -- don't be a hater!
Two miles in 30 minutes is 4 mph -- most people walk at about 3 mph, and even your "30 minutes tops" assumes a steady 4 mph, with no waiting for traffic or anything else. A more reasonable guess at walking two miles for an average walker is 40-50 minutes (the details will depend on delays and just how fast somebody walks.)
And you can pedal an electric bike if you want -- the amount of exercise you get is up to you.
Some people smell more than others after sweating. You can get away without showering, I can too -- but some people can't.
As for not being biodegradable ... um, your non-electric bike isn't biodegradable either. "Recyclable" might be a better metric, and all commonly used rechargeable batteries are recyclable, though a few are pretty nasty for the environment if not recycled (so make sure they're recycled.)
Ultimately, even an electric bicycle is still a bicycle. We should welcome people on electric bikes -- they're not driving their cars, and they're (hopefully) building up the fitness and skills that could help them ride a standard bicycle later.
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How much electricity are we wasting just having this electronic debate? ;-)
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If you knew me, you'd know I was definitely not a hater. I think i came across the wrong way. I'd prefer a non-electric bike, but if electric gets you on a bike, that's great. I just love the feeling that I'm not using any electricity to get me to work. It would be awesome if you put a solar panel on the back for recharging while you are at work.
P "the hater" Larson
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I didn't take you as a hater. :-)
For me personally, a motorized scooter wouldn't give me any advantage over a bicycle, but would add a lot of negatives. Just give me a plain old bike.
John
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It would be awesome if you put a solar panel on the back for recharging while you are at work.
I'm lucky enough to work somewhere willing to pay extra for clean electricity (yay Dell!), and I *do* charge there (inside; I haven't heard of any bikes stolen from the racks outside yet, but this one's my baby and I'm not willing to risk it)... so yes, no fossil fuels burned for the commute.
On a lighter note -- this discussion brings to mind a fellow I ran across online who had purchased a set of home solar panels but whose wife was questioning whether they were money well-spent; he was thinking of buying a high-end ebike to get enough usage of the solar panels to justify their purchase to his wife. That, friends, is chutzpah to aspire to. :)
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The other large reason I vastly prefer my custom ebike for commuting is how much better I can deal with traffic. Breathing heavy on the polluted roads is not healthy. I purposely built my ebike to be *able* to go 35mph if I need. I can pedal my road bike at 30mph for a mile or so, but I'm not doing that in traffic. Real world pedal commuting is more like 10mph uphill (so I don't get super sweaty), 16mph on flat roads, and the reality is at these speeds, you are very vulnerable to autos.
Since I solar charge most of the time, it "feels" great to ride my ebike. Riding on the sun!
3 years ago when I posted in this topic, I had a 2 mile commute to work. I rode a road bike one day and with the hummidity in the morning it was awful, especially on the hills. I just can't stand pedaling in cotton/work clothes. That would mean I have to change out of bike clothes at work. It's an inconvenience.
I come from a road racing background. Maybe that's why I don't need to feel a sense of accomplishment from pedaling as transportation. That's fine if you do, but I much prefer the sunshine to push me around, keep me up to speed with traffic, and not sucking down exhaust fumes (yes, even on the side roads). Yes my ebike is technically illegal. Just like going 70mph in a 65 zone is. Just like jaywalking is. All can be done completely harmlessly and benefit the user. My ebike is the REAL rapid urban transit. Sooo much fun.
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If you knew me, you'd know I was definitely not a hater.
Just to be clear, I was just making a joke at this comment --
Ugh, I hate to hear people using electric bikes for a 2-mile commute.
I'm not sure if the tongue-in-cheekness of my statement came through or not ...
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