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This question already has an answer here:

In the second episode of the first series of Black Mirror, "Fifteen Million Merits", humans' primary way of earning money is by powering pedal-driven electrical generators.

  1. Would human-powered generators like these be a practical method of energy production?
  2. Using this or similar methods, could humans generate more energy than it would take to sustain them?
  3. Would it be economical for an entity/organisation to cultivate humans for the purpose of using them as a power source?
  4. Could an entity/organisation profit by cultivating humans to power electrical generators, to convert their bodies' chemical energy into harnessable electrical energy?
  5. Would there be any benefit to using humans as a power source, milking them of their chemical energy for electrical energy, in a futuristic machine-driven economy where humans have been virtually obsoleted by machines?
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marked as duplicate by kingledion, Thorsten S., Aify, Hohmannfan, JDługosz Dec 12 '16 at 7:33

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ There are a lot of articles about this: google.com/… $\endgroup$ – Thom Blair III Dec 12 '16 at 1:44
  • $\begingroup$ Answer to 2) in always NO. You cannot get from a process more energy than which is available in the inputs (law of conservation of energy). And in fact you will always get less as some of the original energy will dissipate as thermal energy (heat), 2nd law of thermodinamics. It does not matter if we talk about people, bunnies, alien technology, etc. And from that, both 3, 4 & 5 is NO! $\endgroup$ – SJuan76 Dec 12 '16 at 1:58
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No, this is a terrible idea and many a hippie has fallen for it.

Humans can generate 60 to 100 watts sustained on a stationary bike. The room lighting alone would put you in the negative.

You'd get more energy from composting and burning the food to generate steam.

The original script for The Matrix had the machines using humans for their computing power, which made a lot more physics sense than the coppertop explanation in the theatre version.

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  • $\begingroup$ And feeding those humans would put you seriously in the red. In modern society driving is actually usually greener than walking for this reason. $\endgroup$ – Loren Pechtel Dec 12 '16 at 6:57
  • $\begingroup$ The black mirror episode never actually never says the bikers are producing energy, it's somewhat implied that it's just make-work, something to keep the proles exercising and occupied while keeping down their consumption. $\endgroup$ – Murphy Dec 12 '16 at 14:13
  • $\begingroup$ Re "The room lighting alone would put you in the negative." Only if you use incandescent bulbs. LEDs would work perfectly well. $\endgroup$ – jamesqf Dec 12 '16 at 19:48
  • $\begingroup$ LED is just short of a 10-fold gain, and it was very bright when the lights were on. There's a limit to the number of lumens you can produce per watt. The bike screens alone would take more than 100 watts. $\endgroup$ – wyldstallyns Dec 12 '16 at 20:37
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It Depends On What Is Being Powered

If you are trying to light a 60 watt incandescent bulb or a resistance coil stove top, it is incredibly hard to generate enough energy on a stationary bike to keep the bulb lit for very long--I have tried several times at a science museum. You can test it for yourself by going to a gym and trying a stationary bike or rowing machine with a digital readout. They usually have an option for showing how much energy you are expending.

However, if you are trying to light a LED flashlight, a very small amount of energy expenditure can go quite a long way. Take for example the Secur LED flashlight:

enter image description here

It has the following specs:

  • The high power Flashlight comes with a built in Dynamo powered hand crank

  • 8 Lumens 3 LED

  • 3 Function LED: One LED, Three LED’s, Three LED’s Flashing

  • After 1 minute hand cranking:

    • 60 minutes with all 3 LED’s
    • 80 Minutes with 1 LED
    • 110 Minutes of flashing

I have one of these and it's plenty bright enough to use when walking around at night.

So, as you can see, if your electronics use less energy, stationary bike generators become much more plausible.

Increasing Human Endurance

On limit on how much energy people can generate from exercise is muscle fatigue. One possible way to increase endurance is to use respirocytes. Respirocytes are hypothetical, microscopic, artificial red blood cells that are intended to emulate the function of their organic counterparts, so as to supplement or replace the function of much of the human body's normal respiratory system. Respirocytes were proposed by Robert A. Freitas Jr in his 1998 paper "A Mechanical Artificial Red Blood Cell: Exploratory Design in Medical Nanotechnology".

enter image description here

In Freitas' proposal, each respirocyte could store and transport 236 times more oxygen than a natural red blood cell, and could release it in a more controlled manner. Such respirocytes "would allow an adult human to sprint at top speed for at least 15 minutes without taking a breath."

So, with this kind of extra endurance, people could generate a lot more energy on bikes.

Bottom Line

However, the bottom line is if you are trying to replicate modern a society with its current power usage solely by powering it with bicycles, I cannot envision any scenario that can work. How would you heat water, cook food, etc. Human power can supplement power generation, but if you are going to rely on it alone, I think you would be envisioning an extremely primitive, almost stone age level of society, with the exception of LED lighting.

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