Using man-power to turn massive generator

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The discussion revolves around the feasibility of using human power to turn a large generator, specifically referencing the massive generators at the Three Gorges Dam. Participants highlight that while mechanical advantage can be achieved through gears, it does not increase energy output; the total energy produced will equal the energy input. A reasonably fit person can generate about 200 watts of power, but scaling this to run a large generator would require impractically large numbers of people. There are also concerns about the efficiency and practicality of using human labor compared to other energy sources. Ultimately, the idea of harnessing human power for electricity generation is acknowledged as inefficient and not cost-effective.
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Hi

I just wanted to run this hypothetical power plant idea past you physics guys to see what kind of feedback I could get.

My general question is "Could man-power through the use of massive gears, be used to turn a very large generator.?"
The generators used in the Three Gorges Dam(http://en.wikipedia.org/wiki/Three_Gorges_Dam" ) can generate 700MW of power and are about 75 feet in diameter. What kind of force would it take to get this thing spinning? My idea is to build a massive "outer" gear lined with manned pushing posts around the entire circumference. The generator would be in the center. Through the use of many gears that get smaller and smaller, enventually ending up as the rotor of the generator, you could gain massive mechanical advantage. The men would push at a walking pace while the center rotor spun at a great rate. I am picturing 100, 200, 500 men, not sure. Any initial thoughts? I realize there are several unknowns in this. I just want to gets some thoughts rolling. Thanks

Here is a pic of the generator.
http://www.nancarrow-webdesk.com/warehouse/storage2/2008-w25/img.249065_t.jpg"


OOps, I just realized this should be under the engineering section, sorry
 
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A reasonably athletic person can generate perhaps 200 W of mechanical power by pedaling a bike. So if you lined-up 3.5 million people on stationary bikes, you could run those generators with people. It is China!

I'm also not sure you understand what the term "mechanical advantage means". Whether it is a lever or a gear, when you multipy speed (distance) on one side, you have to multiply force on the other. So mechanical advantage yields no increase in power.

Welcome to PF!
 
By having a very large distance (the large outer gear), you would produce a larger force, right? This force would turn the generator rotor which creates electricity. I really don't know how generators work. Is there an increasing resistance as more power is being generated from the generator?
 
Lareg force moving very slowly, yes. Or, you could reverse the gearing and have a very weak force moving fast. But the total energy at the output will be the same as the amount of energy put in (or less).
 
So, if a reasonably athletic person can generate 200W of power. There is no way I could, for example, get this 2400W generator going using just my power with the help of a very large and a very small gear.http://www.grainger.com/Grainger/items/6HJ87"
 
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No. Your problem isn't that you don't understand generators, it is that you don't understand what gears do: mechanical advantage. Read the wik link: http://en.wikipedia.org/wiki/Mechanical_advantage

In short, think about the example of a lever: one end moves a large distance with a small force and the other end moves a small distance with a large force. But the torque and work (or power or energy) done remains the same for both ends. Levers and gears multiply force, not energy.
 
Ok. Thanks for the info. These forums are very informative.
 
tmoney said:
So, if a reasonably athletic person can generate 200W of power. There is no way I could, for example, get this 2400W generator going using just my power with the help of a very large and a very small gear.http://www.grainger.com/Grainger/items/6HJ87"

Not with gears, but you could possibly with a spring (or other energy storage and release mechanism). If you get on the treadmill and generate 200W fo energy for 10 hours, I suppose you could run a 2000W generator for 1 hour.
 
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I have given thought to this concept as well, but from a bit of a different perspective...

Most of us pay taxes to keep prisoners locked up, and fed... so why not put them to work? Assemble a gearing system that links up dozens (maybe even hundreds) of bicycles, and connects them to a massive generator.

If you've got a prison of 800 men... you could divide them up into groups of 200, and schedule them to be always pedaling... say
200 men * 200 watts/hr * 24 hours a day = just under 1 megawatt/day...

this is just an example, and obviously not nearly enough power to power big cities... but surely there are some efficiencies to be gained in a large scale system like this... maybe?

anyway, just a thought.
 
  • #10
bigtruckdrive,

The watt is a unit of power, defined as energy per unit time. The unit "watt/hr" makes no sense. Neither does the unit "megawatt/day."

Furthermore, if you want prisoners to produce mechanical energy, you'll need to provide them an equal amount of chemical energy, as food. (Actually, even more, since human muscles are not 100% efficient.) The big problem is that human food is considerably more expensive, per unit of energy, than many other forms of energy.

A gallon of gasoline contains 35,000 Calories and costs about $4. A pint of Ben & Jerry's ice cream contains about 1,200 Calories and costs almost as much. You'd be much better off sparing the prisoners and just burning gasoline.

- Warren
 
  • #11
hah, i guess that is a good point. hadn't thought of that.

I guess you'd have the prisoners putting out a decent amount of CO2 as well...

Although I wonder, if the energy they are burning is from a low cost food source, like rice or pasta, this might be more feasible?

It seems to me that this is a resource we should take advantage of! lol
 
  • #12
Your calculation produced 1 megawatt-hour per day of energy or 40 kilowatts of power. That's not very much. Just as a benchmark, commercial office space runs around 5 watts per square foot in the summer. So your 40 kW gives you enough power to run 8,000 square feet of office space.
 
  • #13
Ya, seems like the power produced would be negligible. If anything I supposed this generated power could be use to power the prison...
 
  • #14
I think it's a good concept. I have long held the position that there should be no such thing as "hard labor" as a separate sentence for convicted criminals. It should be understood as part of their sentence that they will work rather than sit around living off of taxpayer's money. But, I suppose that putting them on bicycles to power an air compressor so a jack hammer can split rocks is inherently less effecient than putting a sledge hammer in their hands and having them whack away.

Still, the comparrison to gasoline does not take into account the fact that, if these men do not use their energies to do work, they are still going to burn those callories, so you don't save that energy by not putting them to work. There must be some practical way of using all this manpower to defray some of the expense of operating the prison.
 
  • #15
I had thought of the prison idea as well, and these guys would already be eating and burning calories bench pressing or beating up their cell mates. You might as well harness those calories.

I like the idea of man-generated electricity. The human animal doesn't need electricity to survive. Humans have produced a society that requires electricity. It should be Human's that do the work to produce it instead of harnessing various forces of nature.
 
  • #16
tmoney said:
I had thought of the prison idea as well, and these guys would already be eating and burning calories bench pressing or beating up their cell mates. You might as well harness those calories.

I like the idea of man-generated electricity. The human animal doesn't need electricity to survive. Humans have produced a society that requires electricity. It should be Human's that do the work to produce it instead of harnessing various forces of nature.

Humans are very weak an inefficient at producing energy mechanically. But with just a few watts of electrical energy, our brains can devise ways of harnessing other sources of energy far greater.

Instead of putting a thousand prisoners to work moving boulders, you should stuff them in the library and force them to learn physics & engineering. :)
 
  • #17
Hmm, good observation. I guess we have created a monster that we can no longer feed, and we are took weak to do what it does for us.
 
  • #18
Hi guys, my first post! I really enjoyed reading this thread, it's funny and intelligent - a great combination.

I found this site trying to work out the power a person can generate (not just consume).. you know how it is, ideas, nothing to do, calculator itching for numbers..

My physics is a little rusty so I really enjoyed reading this post. It looks like a few keen minds are as rusty as me and the perhaps improper use of some of the terms used is caused by not fully understanding them. Things like what power, leverage or a KW/h actually is.

What roused my interest is the 200W a 'reasonably fit' person can produce. Am I right to think you mean this in a calorie/joule - energy ratio per hour?

An average althetic male will use about 1700 cals a second (612Kcal hour) playing squash - intense physical exersion. A watt is the SI derived unit of power, equal to one joule of energy per second. Ergo 1W = 1J/s. 1 calorie = 4.18400 joules (4.2W) which equates to 7112.8W or about 7Kw second for the squash player. As Watts and Joules are time oriented, we can't multiply this out to infer a human will generate 25MW/h! I understand this healthy person is capped out at 7Kw/h (I said I was rusty).

I can only understand from tmoney's original question (also with reference to https://www.physicsforums.com/showthread.php?t=299004" Force Needed to Turn Generator at Maximum Output post) that from 6 hours (hard labour a day) would equate to (7Kw/h * 6 hours) 42KW/h day.

I see one obvious flaw (aside from my maths) in the fact that we would expell 7112.8W a second just to do the work so any device used to capture the energy would be less efficient. Some of the most efficient alternators are about 80%, but it's interesting to imagine how much real-power can be produced from pure grunt. In honesty my interest comes from thinking the gym in itself is a waste of time and quite literally - energy. It would be interesting to save it up and use it at home squashing the electricity bill, staying fit, or do I just need to get out more? :smile:
 
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  • #19
"Could man-power through the use of massive gears, be used to turn a very large generator.?"You're going to require cheep labour fir that...so why not go to India to try it?

can generate 700MW

Considering the efficiency of this thing is not 100% you're going to require men so as to generate this much amount of energy in a limited time interval.
Feed them well! :)
 
  • #20
The image says not for public use.
 
  • #21
No body discusses the man's old friends, Bulls and Elephants. What if they are substituted as prime movers? I hope it would dropm the workers figures in million to some less number. Other than that it would help save wild life.
 
  • #22
robotbender said:
What roused my interest is the 200W a 'reasonably fit' person can produce. Am I right to think you mean this in a calorie/joule - energy ratio per hour?
Welcome to PF.

A calorie/joule doesn't make any sense to me. No, 200W is 200W. It is the power that they generate (ie, by pedaling a bike).
An average althetic male will use about 1700 cals a second (612Kcal hour) playing squash...
You have an extra zero in there: 612000/3600=170 cal/s.
A watt is the SI derived unit of power, equal to one joule of energy per second. Ergo 1W = 1J/s.
Yes.
1 calorie = 4.18400 joules (4.2W)...
Now you are mixing power and energy. 1 cal is 4.18 J or 4.18 w-s.
...which equates to 7112.8W or about 7Kw second for the squash player.
Same error carried forward: 170 cal/s *4.18 J/cal = 710 J/s or 710 W
As Watts and Joules are time oriented, we can't multiply this out to infer a human will generate 25MW/h! I understand this healthy person is capped out at 7Kw/h (I said I was rusty).
You're realizing there is a time element there, but using it incorrectly. There is no such thing as a MW/h or KW/h. MW and KW are already a rate, in terms of seconds. To get power, you multiply by time. Energy from a power plant is measured in KWh or MWh, which is killowatt-hours or megawatt-hours: 1000 and 1000000 J/s-h.
I can only understand from tmoney's original question (also with reference to https://www.physicsforums.com/showthread.php?t=299004" Force Needed to Turn Generator at Maximum Output post) that from 6 hours (hard labour a day) would equate to (7Kw/h * 6 hours) 42KW/h day.
Again, these units are wrong and the decimal error is carried forward: 700 W for 6 hours is .7*6 = 4.2 KWh per day.
 
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  • #23
I don't take anything for granted, and I don't believe everything I am told. I like to put things to the test. So does anyone have an idea, for some way to test this theory?

I would think using a controll, of one man, healthy enough to turn a turbine or generator of
some kind, to see how much energy he can produce by turning a lever let's say, would be simple enough. however
Not all men are equall.
And I don't like the idea of using a bycicle, to see how much energy is produced. (you are only using your legs)

what I would like to see, is a small wind turbine on the ground, positioned so blades were parellel to the ground, and see how many men it would take to turn the blades of the turbine.
Unless someon has a calcutlon they coudl run to show that this would be an impossible act?

I would even be up for planing an event at some location, gathering some able bodies up,
and testing this theory.
 
  • #24
Any elliptical machine will use both your arms and legs and already tells you the power output. If you don't believe it you can hook it or a bike up to a generator. There is no need to get convoluted and complicated.

I'm not sure you will get many people who don't believe what their exercise bike is telling them so you may need to just do this yourself.
 
  • #25
russ_watters said:
Any elliptical machine will use both your arms and legs and already tells you the power output. If you don't believe it you can hook it or a bike up to a generator. There is no need to get convoluted and complicated.

I'm not sure you will get many people who don't believe what their exercise bike is telling them so you may need to just do this yourself.

I hear what you are saying. I could measure what my own output would be. But my problem with this theory is that we are bassing these calculations, on what one man can do. I am terrible at explaing these things, but I will try:
I can peddle my bike at a maximum sustained speed of 17 miles an hour, on flat ground.
In our equations, we are assuming that if we add another man to the bike, we can now go 17 x 2 = 34 miles an hour.
But this is not true. Haveing a tandum bike does not meen you go twice as fast.
The reason being is you are limited by the bike itself. the gears are too small, there is greater wind resistance, ect.

In essence, what we would have to do is make the the gears bigger.

Let's say you have (2) men in a room with a stationary bike. no wind. no road friction.
It would stand to reason that (2) men, could move the same gear, that is twice the size of the gear, that a single man can move.

What I am saying, is that (2) men could move a gear that is 2 1/2 times the size.
Maybe even more.
 
  • #26
markplans2 said:
I hear what you are saying. I could measure what my own output would be. But my problem with this theory is that we are bassing these calculations, on what one man can do. I am terrible at explaing these things, but I will try:
I can peddle my bike at a maximum sustained speed of 17 miles an hour, on flat ground.
In our equations, we are assuming that if we add another man to the bike, we can now go 17 x 2 = 34 miles an hour.
But this is not true. Haveing a tandum bike does not meen you go twice as fast.
The reason being is you are limited by the bike itself. the gears are too small, there is greater wind resistance, ect.

In essence, what we would have to do is make the the gears bigger.

Let's say you have (2) men in a room with a stationary bike. no wind. no road friction.
It would stand to reason that (2) men, could move the same gear, that is twice the size of the gear, that a single man can move.

What I am saying, is that (2) men could move a gear that is 2 1/2 times the size.
Maybe even more.

It's possible that the human body could be more efficient at pushing a lever with high force at low speed (I have no idea if this is the case). However the maximum product of the two (force * speed = power) is still limited by what the average human body can continually produce due to physiology.
 
  • #27
The most efficient way to harness human-generated energy, imo, is to put people in warm clothes when it's cold and have them do exercise or labor to warm themselves. I have experimented with this and found that I can live comfortably as low as 40F with a warm coat and hat/cap. Compare the amount of calories/joules/btus necessary to bring a house from 40F to 65F and the amount your body needs to generate to keep you feeling toasty in a sweater or coat with hat and gloves? If you're doing exercise or labor, you might even need to shed some of the clothes.
 
  • #28
Hallo every one, I was very surprised and happy at the same time to find out there is a Forum investigating about this interesting issue on which I’m thinking since some time. For this reason I just got registered and wander if we could continue to analyze and expand the subject more in details, scientifically in all aspects related to the use of man-power to produce electricity, not only for prisoners but also for poor communities where having access to few kWh of electricity it could mean much more the better welfare.
I personally would be very interested to study the idea of introducing this opportunity into prisons, (that it shouldn’t be an obligation to my opinion) I’m convinced there would be a number of interesting advantages, such as:

1. producing something (you said 4-5 kWh, maybe by using a more efficient equipment it could be increased ?) it would be good for the environment and the society while reducing the prisoner public cost.
2. while the man is physically at work pedaling, with legs and/or even with arms, at the same time he could still use the brain and apparently without disturbing his concentration with good result for both mind and body activities.
3. the activity is proved of being an important health factor, “Mens sana in corpore sano” (healthy mind in healthy body) there should be experiments already done that can tell us more about it.
4. More chance for him to understand how to behave in order to reduce his penalty, to learn more about social relation and how to plan his future after being released.
5. He will be, mentally and physically busy in doing something good for him self and the society, reduce stress on him as well as on the every one else around him and feel less useless
Many other positive aspects could be listed if you like……
Thanks for your attention and Regards
Maroki
 
  • #29
Jeez, just use hamsters or rabbits.
Or maybe horses... horsepower :)
 
  • #30
Well… you missed to mention the donkey-power or the mule-power….which, you should know, are the most efficient among them all, but in all cases, palladin…..instead of funny nonsense why not opposing scientific or at least reasonable questions, if you have any?
 
  • #31
Maroki said:
Well… you missed to mention the donkey-power or the mule-power….which, you should know, are the most efficient among them all, but in all cases, palladin…..instead of funny nonsense why not opposing scientific or at least reasonable questions, if you have any?

Well... human powered generation of usable force has been around for a very long time.
On a low-scale level, say, a hand-crank radio or flashlight all is good. Or paddles for a canoe.
On a scale exceeding this it becomes functional ridiculous; given current technological alternatives.
 
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  • #32
Maroki said:
1. producing something (you said 4-5 kWh, maybe by using a more efficient equipment it could be increased ?) it would be good for the environment and the society while reducing the prisoner public cost.
It wouldn't really be good for the environment. Humans generate a lot of CO2 when producing mechanical work, and the fuel for humans requires a lot of fossil fuels to produce, distribute, and prepare.
 
  • #33
DaleSpam said:
It wouldn't really be good for the environment. Humans generate a lot of CO2 when producing mechanical work, and the fuel for humans requires a lot of fossil fuels to produce, distribute, and prepare.

Yeah you would be better off just burning food in a boiler to run a steam turbine then feeding it to people to do manual labor. :p
 
  • #34
a lot of CO2, when producing mechanical work?…yes ok, but how much?
maybe you do know that before the industrial revolution, before carbon fossil fuel came into the scene I mean, a farmer or one man could produce four (4) calories per each calorie spend in his work;
and maybe you do know also that thanks to the carbon fossil fuel now one man can produce many times more finished products then before (hundreds or even thousands times) but for each calorie it is burned ten (10) calories.
How much of CO2 is producing this type of mechanical work?
Let us go into numbers if possible please.
 
  • #35
Maroki said:
How much of CO2 is producing this type of mechanical work?
Let us go into numbers if possible please.
I am sure you can find the numbers with a bit of research.
 
  • #36
The CO2 animals exhale should be a net neutral as far as total CO2 in the atmosphere goes. The CO2 came from plants which captured the CO2 that was already in the atmosphere. The plants would have released that CO2 when they decayed if they weren't eaten.

The only carbon which affects the global total CO2 levels is carbon which is either being sequestered long term, or being released from long term sequestering, in other words, fossil fuels. Modern farming certainly uses lots of external energy provided mainly by fossil fuels, so it is still valid to say that humans consuming extra food will raise the CO2 levels. To answer how much the levels will raise one needs to find out how much fossil fuel was burned to produce the extra food.

As for the amount of energy needed to produce food, a brief search shows widely varying numbers. Many sites seem to cite one study in particular. It may be a good idea to read through it if you have an interest:

http://dieoff.org/page55.htm
 
  • #37
Thank you Dale, this is a nice and constructive approach I think may really help. I will read that and be back ASAP.
 
  • #38
DaleSwanson said:
Modern farming certainly uses lots of external energy provided mainly by fossil fuels, so it is still valid to say that humans consuming extra food will raise the CO2 levels. To answer how much the levels will raise one needs to find out how much fossil fuel was burned to produce the extra food.
Yes. That and also you need to consider what the impact of agricultural land use is. E.g. if you clear cut an acre of rainforest in order to plant food you have a huge carbon impact from that also.
 
  • #39
DaleSpam said:
Yes. That and also you need to consider what the impact of agricultural land use is. E.g. if you clear cut an acre of rainforest in order to plant food you have a huge carbon impact from that also.

Good point, I over looked that originally, probably because I was thinking mostly in terms of the US where I don't think it is as likely to happen. It were certainly be harder to estimate the impact of converting forest to crops, since it is a one time only event. I suppose you could find numbers for how much forest is being converted to crops annually worldwide and then figure out how much less carbon the living crops hold than the living forest.
 
  • #40
Howuuu…..Thanks to both Dales...here "[URL in this report dated 1994 there is every thing one should know, analysing, expanding and unfortunately confirming, the models already perfectly foreseen back in 1972 by The_Limits_to_Growth..."[URL

And here ……. "[URL

…..“In a very real sense, we are literally eating fossil fuels. However, due to the laws of thermodynamics, there is not a direct correspondence between energy inflow and outflow in agriculture. Along the way, there is a marked energy loss. Between 1945 and 1994, energy input to agriculture increased 4-fold while crop yields only increased 3-fold.11 Since then, energy input has continued to increase without a corresponding increase in crop yield. We have reached the point of marginal returns.”

More over ….
“there are two separate forms of (human) energy input: Endosomatic energy and Exosomatic energy. Endosomatic energy is generated through the metabolic transformation of food energy into muscle energy in the human body. Exosomatic energy is generated by transforming energy outside of the human body, such as burning gasoline in a tractor. This assessment allowed the authors to look at fossil fuel input alone and in ratio to other inputs.
Prior to the industrial revolution, virtually 100% of both endosomatic and exosomatic energy was solar driven. Fossil fuels now represent 90% of the exosomatic energy used in the United States and other developed countries.17 The typical exo/endo ratio of pre-industrial, solar powered societies is about 4 to 1. The ratio has changed tenfold in developed countries, climbing to 40 to 1. And in the United States it is more than 90 to 1.18 The nature of the way we use endosomatic energy has changed as well.
The vast majority of endosomatic energy is no longer expended to deliver power for direct economic processes. Now the majority of endosomatic energy is utilized to generate the flow of information directing the flow of exosomatic energy driving machines. Considering the 90/1 exo/endo ratio in the United States, each endosomatic kcal of energy expended in the US induces the circulation of 90 kcal of exosomatic energy. As an example, a small gasoline engine can convert the 38,000 kcal in one gallon of gasoline into 8.8 KWh (Kilowatt hours), which equates to about 3 weeks of work for one human being.19” ….
…..10 kcal of exosomatic energy are required to produce 1 kcal of food delivered to the consumer in the U.S. food system. This includes packaging and all delivery expenses, but excludes household cooking).20 The U.S. food system consumes ten times more energy than it produces in food energy. This disparity is made possible by non renewable fossil fuel stocks. …..”

Therefore I would like to conclude that since most of the energy we consume the way we do it now is causing from one side the running down of natural resources and from the other side, pollution and climate change, whether we like it or not, we will have to better structure our mind in order to make good use of every single calorie, the sooner we do that and the less pain we will have facing the next coming revolution.
 
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  • #41
The answer of my friends, is blown in the wind...?
 
  • #42
I see this thread ended long ago but giving this a shot...

Going back to the original question of using gears to power a large generator... What I have been wondering about is whether I could put together 1 or 2 of the 250 watt solar panel kits and use it to power a small electrical motor which would be used to turn something like a 3-8 kw generator for my home. This would cost significantly less than outfitting my house with enough solar to produce the same amount of electricity but would likely need a gearing system to spin the big generator fast enough. I am assuming I am missing something here or this would be common practice?

I have spun a 5 kw gen by hand and can light a light bulb, it isn't difficult to turn, but needs to be spun pretty fast to hit full output obviously.

OK you smart people, what do you think? :-)
 
  • #43
Welcome to PF!

Mechanical power in = electrical power out. You can't get something for nothing.

That generator that you spun by hand that was connected to one light bulb: try connecting 10 light bulbs to it and see if it is harder to spin.
 
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