How Many Cyclists does it Take to Power a Hairdryer?

[bhikkhu]

The aim of the experiment was to illustrate in terms we can all understand - pedal power - just how much energy we use and to highlight the effort it takes to create the power we need, as opposed to simply flicking a switch. The experiment, without doubt, provides food for thought.

The cyclists were not normal people, or even those used to participating in the hell that is a gym-based cycling 'spinning class', but instead were members of some of Britain's most elite cycling clubs. You might think they would find the task easy. Yet simply powering a hairdryer relied on the efforts of 18 cyclists. It took nine cyclists to power the toaster. And boiling the kettle, something most of us do a number of times a day, requires the combined effort of 30 cyclists pedalling as fast as possible.

The list goes on: three cyclists for the television, 11 cyclists for the vacuum cleaner, 15 cyclists for the iron, 14 for the microwave, 17 for the washing machine, 24 for the oven and an astonishing 70 cyclists pedalling at full-pelt just to power the electric shower.

At one stage, when the family were simply doing what they would ordinarily do on a Sunday afternoon - the children were playing on the Wii, Andy was vacuuming, Shelley was cooking a roast, and yes, a few extra lights had been left on, the house was plunged into darkness as all 80 cyclists, despite pedalling full-tilt, were unable to keep up with the energy demands.

Read more: http://www.dailymail.co.uk/sciencetech/article-1232743/How-cyclists-does-power-hairdryer-The-answers-18-family-discovered-unique-TV-experiment.html#ixzz0Ypwm4gLu

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...a very well thought out experiment, and a well written article. I ride about 20 miles a day myself so I have wondered about it. It is interesting that they valued the total power output at the end of the day at 2 or 3 dollars, while the cyclists probably consumed a thousand dollars worth of food in the course of generating the energy. If you then go one more step and look at the energy that went into producing the food, and figured the size of the army of cyclists it would take to provide that, and so on...it boggles the mind.

We have it so easy at present.

[TreasonousBastard]

1. "The average human can maintain 40 or 50 watts for an hour"...

while a trained athelete in top shape could do 10 times that for a while. So, it would take me about 20 hours to generate a kilowatt, if I could keep cycling that long.

Ain't a whole hell of a lot of juice with people-power.

[Fumesucker]

27. I'm under the impression it's a bit more than that for the "average human"

I'll be sixty next year and I can do about ninety to a hundred and twenty watts for an hour or more when I calculate back from my speed on my bicycle for that length of time.

It's interesting how the duration of effort falls off very quickly with increasing output.

[TreasonousBastard]

28. Maybe you could, but that number was from the article and...

was for the "average" person, whatever that may mean. Perhaps you are above average in this case.

Either way makes little difference, though, to the point that human-power won't get us very far.

[Fumesucker]

30. Forty watts is only 7.1 mph on a draggy bicycle with knobby tires..

http://www.me.psu.edu/lamancusa/ProdDiss/Bicycle/bikecalc1.htm

And I guessed you missed the graph I posted..

[TreasonousBastard]

31. I didn't miss a thing-- a hand-drawn graph with no...

references means very little. A web calculator with so many variables means little more.

Maybe the article got that part wrong, maybe it didn't, but nothing you or that other guy arguing about it invalidates the point about human power being far from the next big thing.

[madokie]

36. I'm old and disabled

but I moved one ton of wood pellets that come in 40 lb bags an average of 16 ft in 21 minutes. did this twice with two seperate loads of pellets. I was going to figure out my hp by that but never got around to it. ;-)

[Laelth]

2. Very interesting. Thanks. k&r n/t

:dem:

-Laelth

[LearnedHand]

3. Wow! What a GREAT article k&r

Thanks so much for posting.

[OffWithTheirHeads]

4. The electric shower?

Is that one of those like Halliburton was building for our troops in Iraq?

[bhikkhu]

6. I'd imagine it was a "hot water on demand" type device

which is more popular in Europe than here. An electric one is just a rapid heating coil, typically 220 volts and fused at 20 amps or so, which is capable of heating a continuous flow of water for a shower or hot water tap. This is one option to keeping hot water stored in a tank.

I think the difference in the military versions is the assumption of water pressure.

[OffWithTheirHeads]

12. My understanding is that this type of device is very innefective.

In this country, only instant hot water heaters powered by natural gas seem to work well. I'd love to have one in my all electric home but even the suppliers say they suck.

[bhikkhu]

14. At my job we have an electric one on the bathroom faucets

It works well enough, though the flow is probably much less than you'd need to shower. I imagine the only real savings would be over a hot water heater without a good insulating jacket, or a hot water heater located a long distance from the bathrooms.

I have a good efficient gas powered hot water heater, but our house design has one flaw: the kitchen and laundry room are on one side of the house (with the water heater), and the two bathrooms are on the other side. We have to run the showers or taps awhile before we get hot water, even with the pipes insulated.

[madokie]

37. that uses the resistance of skin to create the heat

[mike_c]

5. that's an excellent demonstration of the energy density of fossil hydrocarbons....

Nicely done!

[Nay]

11. Yes, it is, and it also demonstrates the very real problems of replacing

fossil hydrocarbons with any of the available alternatives.

[wtmusic]

7. 18 experienced cyclists to power a hairdryer? Nonsense.

Lance Armstrong routinely generates 500 watts:

http://www.nytimes.com/2005/06/14/science/14cycl.html

and a fit club cyclist can easily generate 300. It would take 4 to run a 1200W hairdryer.

And a thousand dollars worth of food? A 1 lb bag of rice (cooked) would allow 4 humans to generate 1200W for about 12 minutes, based on 20% thermal efficiency. The cost is between $1-2.

Another glaring mistake:

"Their peak output was 12 kilowatts per hour, enough to run four kettles"

Equivalent to saying "the car's top speed was 120 miles per hour, per hour"

[bhikkhu]

9. They were talking about sustainable effort

A sprinter can put out 1300 watts, but that doesn't last long. Armstrong in top form (which is to say - in a condition which takes much of a year to train up to, and which few professional athletes ever reach) could do 500 watts for a couple of hours, but he wasn't there and the efforts had to last through the day in any case.

The thing most people not deep into sports miss is the difference between a professional athlete in top form and an "average" athlete. The numbers the article provides are the real numbers of a real experiment, rather than ballpark guesses based on ideal conditions.

You can calculate the conversion factors and caloric values of food well enough, but just try to feed 80 athletes during what was basically an endurance event for $12 a head. I think you'd be out of volunteers halfway into the experiment. As a cyclist myself, during the summer the extra miles convert directly into a larger food bill and there's not much to be done about it.

Saying "12 kilowatts per hour" is, I assume, the same as saying 12 kilowatt hours, which is the usual way of talking about a quantity of electrical energy.

[wtmusic]

10. My point is, the comparison is meaningless.

I'm sure you could find cyclists in bad enough shape to require 200 of them. What's the point? You have it exactly backwards - I've provided real numbers, and they've provided not even ballpark guesses in their "real" experiment.

They're screwed either way with their energy measurement, as there is no such thing as a "peak output" of 12kWh.

Sorry, but I lose patience with junk science, and that's what this is.

[bhikkhu]

13. Well, so you do have a point

Cyclists in any condition aren't likely to ever be used for power production. So you could say its "junk science" to see how many it takes to power our appliances and so forth.

I tend to look at it the other way, though, as the article said: "The aim of the experiment was to illustrate in terms we can all understand - pedal power - just how much energy we use and to highlight the effort it takes to create the power we need"

I think it did very well.

I still don't get the problem with the "peak output was about 12 kilowatts per hour" statement. Kilowatts per hour is standard terminology, and in context its clear they're talking about the maximum energy output the group as a whole was able to maintain. 12000 watts divided by 80 riders gives 150 watts per rider average as the peak output, which makes sense and sounds about right. They talked about one period when the whole group was working and only brief breaks were rotated through the group of 80 so it was probably then. I don't know what other words or language they could use for that.

[wtmusic]

15. "Kilowatts per hour" makes no sense

Watts are a measurement of the rate of energy conversion. 1 watt = 1 joule of energy converted every second. 1 kilowatt = 1000 joules converted every second.

1 kilowatt per hour = 1000 joules converted every second every hour :silly:

At the Museum of Science and Industry in Chicago there's a bicycle you can get on and pedal to light up a 100W light bulb. Most visitors are surprised at how hard they have to pedal, and it's a valid demonstration. Trying to assign pseudoscientific data to it is like doing a study of how many angels can fit on the head of a pin.

[bhikkhu]

16. kWh. Look it up. n/t

[wtmusic]

17. Two different things

Kilowatts per hour = kW/h

Killowatt hours = kWh

Division vs. multiplication.

[bhikkhu]

22. I get it now

1 kw is a unit of energy the same as 1 kWh is a unit of energy. To say 1 kw per hour was produced is like saying 1 kw was produced each hour, which is a whole different thing than saying 1 kWh was produced. So that was sloppy writing.

It was hard to catch largely because it was so clear in context what the writers meant to say, but be that as it may...you are right on that point.

[wtmusic]

24. actually...

watts (and kW) are units of power, which is the rate energy is being used up.

If you look at a quantity of energy as a bucket of water, watts would be analogous to how fast the water is being poured from the bucket.

So if a 100W light bulb uses a trickle of water, a 1kW light bulb would use a stream of water which empties the bucket 10x as fast.

Assuming your bucket has enough water to pour a 1kW stream for an hour, it would originally have held 1kWh of water. So both kWh and joules are measurements of energy - the amount of water in the bucket.

It took me a long time to understand this, I think partly because the terms are so often misused. Electronics is rife with such misunderstandings, possibly the biggest of which involves the direction of current flow in a DC circuit. Though electrons flow from the negative terminal of a battery to the positive, the generally accepted idea is that current flows in the opposite direction - an idea that has no logical basis but has survived by convention (from a work standpoint it doesn't matter which way the current flows).

[kristopher]

26. No he isn't.

He is correct on the difference of kw/hour vs kwh but I don't believe it applies to what was cited. You were correct when you described as referring to a sustained effort. The article explicitly describes the point as "their peak output was 12 kilowatts per hour".

It was an awkward way of saying that was the peak level of performance the human generator could maintain for that period. It is no more awkward than any other truncated way of putting it would be.

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=115x220275#220485

I think the problem is that "per" is ambiguous; it isn't just a division symbol it is also synonymous with "for each".

[kristopher]

18. You might want to reconsider that...

1000 joules x 60 sec x 60 minutes = 3,600,000 joules.

From wiki:

The standard unit of energy in the International System of Units (SI) is the joule (J), equal to one watt second. Inversely, one watt is equal to 1 J/s. One kilowatt hour is 3.6 megajoules, which is the amount of energy expended (or dissipated) if work is done at a constant rate of one thousand watts for one hour.
Examples

A heater, rated at 1,000 watts (1 kilowatt), operating for one hour uses one kilowatt hour (equivalent to 3,600 kilojoules) of energy.

Using a 60 watt light bulb for one hour consumes 0.06 kilowatt hours of electricity. Using a 60 watt light bulb for one thousand hours consumes 60 kilowatt hours of electricity.

If a 100 watt light bulb is on for one hour per day for 30 days, the energy used is

100 W × 30 h = 3,000 W·h = 3 kW·h or 10.8 million joules.

The only difference between kilowatts per hour and kilowatt hours is that one is describing an ongoing rate of flow while the other is describing an aggregated amount of electricity.

So I would describe your reference to division and multiplication as being accurate, but also say that your application to the matter is more along the lines of nitpicking.

The example you offered was: "Their peak output was 12 kilowatts per hour, enough to run four kettles" of which you said, "Equivalent to saying "the car's top speed was 120 miles per hour, per hour".

It would actually be in line with bhikkhu's characterization of it as a description of sustained effort: the PEAK LEVEL THEY WERE ABLE TO MAINTAIN FOR A DURATION LONGER THAN AN HOUR was 12 kw.

While the writing might be a little bit ambiguous I think it is as largely clear as it needs to be.

[wtmusic]

20. Division vs multiplication = nitpicking?

:rofl:

You are so scientifically and mathematically illiterate it is mindboggling.

Now back in your ignore barrel, punk. :hi:

[kristopher]

25. And you misread yet again...

The difference can be important, however it they haven't misused it in the article so while you stated a fact, that fact isn't germane to what is written in the article. You MISREAD the original.

[TreasonousBastard]

29. They did the experiment, but you have the real numbers? Just how...

does that work?

[Nihil]

32. I think you missed the point of the programme.

I watched the programme with my daughter and we both found it fascinating.

> I'm sure you could find cyclists in bad enough shape to require 200 of them.
> What's the point? You have it exactly backwards - I've provided real numbers,
> and they've provided not even ballpark guesses in their "real" experiment.

The point was that the family concerned didn't know what was special about that
day and so behaved as normally as they could. In doing so, some of them wasted
a lot of energy. That message was driven home quite effectively by the use of
"pedal power" rather than just reading out the numbers involved.

The reason they used fluffy terms like "average person" was that they had a
wide range of real people on those bikes: some in their late teens, some who
were in their 50s (maybe 60s for a few), some who were "casual cyclists", some
who did velodrome sprinting at club level and others who did marathon races.
(ETA: Describing them as "members of some of Britain's most elite cycling clubs"
was a bit of Daily Mail-ism - they were members of some of the local cycling
clubs which, as noted above, had a much wider range of ability than might have
been assumed from a straight reading of the review article.)

The point was that instead of noting "Mum has had the oven on for over forty
minutes now without putting the chicken in and this has wasted XY.Z kWh" you
saw the people pedalling like mad, sweating to keep the supply needle out of
the red zone and for what? For the sake of absent-mindedness wasting those
XY.Z kWh.

When the family left the house in the afternoon for a walk in the fresh air,
they still had to keep a surprising number of cyclists active - more than
would be expected to keep the fridge ticking over - so inspected the house
to find out what was drawing the "extra" power. They found the power shower
on standby (rather than off), several small devices on standby (iPod charger,
laptop), a television and a couple of lights left on. Again, seeing people
having to keep pedalling to power up simple thoughtless wastage brings the
message home to a lot more than just providing the number of kWh involved,
especially when you start multiplying that one "average" home by the number
of them in the country.

> Sorry, but I lose patience with junk science, and that's what this is.

No, this wasn't "junk science", it was all about "waking up people" and it worked.

Maybe if you saw the programme rather than just someone's write-up of it, you
would change your mind.
:shrug:

[joshcryer]

8. What's wrong with using a towel? :P

I never understood why one would use a hair dryer.

[Dead_Parrot]

19. Depends how quickly it accelerates

(Measured in KW per hour)
;)

[wtmusic]

21. Thank you D_P

as usual, the most intelligent post in the thread

[Dead_Parrot]

23. doesn't say much for the rest of it, then

:P

[HamdenRice]

33. Imagine the energy saving of cycling over driving!

How many cyclists would it take to power a car?

[wtmusic]

34. A midsize SUV going 50mph requires about 20hp

1 hp = 745.7 watts

745.7 * 20 = ± 15kW

So about 30 Lance Armstrongs pedaling their asses off.

[bhikkhu]

35. Lots of people commute and run their errands by bicycle

Other than trying to get 25lb bags of potatoes and rice and so forth home from the grocery store, it works fine, feels great and saves a great deal of money. Once a week I grocery shop with my wife's car, that's about it.