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Human power

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The conversation surrounding energy consumption in the United States often hones in on dependency on foreign oil, the extent to which fossil fuel consumption contributes to global climate change, etc. Certainly, these are very pressing problems that will need to be addressed soon, but there is a second energy crisis that often is overlooked. While developed nations consume fossil fuels at an alarming rate, nearly 2 billion of the world's population is without electricity and is still heavily reliant on traditional fuels such as dung, wood, and other forms of biomass. [1] Thus far, efforts to reverse this trend have focused on a two-pronged approach: one, increase access to "modern" form of energy in an inexpensive, responsible way; and second, to make the current use of biofuels safer and more sustainable. While this is a worthwhile approach, it is not comprehensive.

For centuries, human and animal power have been utilized, and their importance in the portfolio of a comprehensive strategy for addressing the energy crisis in developing countries should not be ignored. An estimated 1200 petajoules were produced by humans without electricity for the purpose of work in the year 2008. This is over 1.5 times that of wind energy produced in the same year![2] Much of this effort was expended in menial, repetitive tasks that can be made more efficient with human powered machines.


In last twenty years, more attention has been paid to harvesting human energy in more unconventional ways. For instance, piezoelectric crystals, which produce electricity under tension or compression, are becoming cheaper and less fragile. Although their electrical production is very small, it is hoped that an array of such devices could be integrated into clothing to obtain the vibrational energy of a person, for the purpose of powering mobile electronics. [3] [4]


Pedal Power in the United States [6]

Old man [7]

Design Considerations


Fig 1. An cartoon from Punch magazine, 1895, which demonstrates changing cultural norms regarding women and bicycles[8]



Fig 1. Power requirements for common electrical applications [9]

Candidates for human power [10]

Fig 1. Proposed coupling of a hand pump for pedal power [11]

Power generation for lights

Fuel based replacer [12]

Rowing machine [13]

high capacity vehicle [14]

Washing Machine [15]

Human physiology [16]


The natural action of pedaling a bicycle, essentially transforming linear motion into circular motion, creates an oscillatory power function as seen in Figure 2.

Fig 2. Relative power outputs throughout the crank cycle [17]

In the case of a mobile bicycle, this effect is masked by three factors: inertia provided by the weight of the rider; frictional losses from equipment; and drag forces from the air. For stationary riders (people operating human-powered machines), however, this phenomenon comes becomes an important consideration in power delivery. For instance, for the milling of grains, it would be favorable to provide a more or less constant power to mill, to facilitate a consistent feed rate through the machine. For this reason, it is often prudent to introduce a means of “smoothing” the power output from the driven gear. The most common way of this is through a flywheel. A flywheel is a rotating mass used in mechanical systems for energy storage. It will substitute for the inertial mass that the rider's weight provides in the mobile example.

For a circular hoop (imagine a bicycle wheel) of radius 'r' and mass 'm', moment of inertia I, is defined by [math]I_z = m r^2\![/math]

For a solid disk or cylinder of radius 'r' and mass 'm', the moment of inertia I is given by [math]I_z = \frac{m r^2}{2}\,\![/math]

Additionally, the kinetic energy of a flywheel is given by [math]E = \frac{I \omega^2}{2}\,\![/math] where [math]\omega[/math] is the angular velocity of the flywheel.

From initial inspection, we can see that for the same mass, the hoop has a higher moment of inertia, by a factor of 2. From an energy perspective, as compared to a solid cylinder, the hoop takes twice as long to reach a steady speed, but takes twice as long to slow down, all things held equal. The primary advantage of a solid-disk flywheel, however, is ease of manufacture.

There have been several proposed designs for a method of power smoothing that does not require a spinning mass. In particular, a reciprocating spring system and an electrical circuit employing a large capacitor have been suggested. [18] Such systems seek to the portability of human-powered machines. While the massless mechanical system has not seen wide distribution, the later has found use in electrical power generation, in applications that require steady voltage input.[19]


Fig 3. Example of a two-man dynapod [20]
Fig 4. Realization of a one-man dynapod for threshing grain in Uganda [21]

drawbacks of bike-based generators [22]


In the realm of electrical power generation, a notable participant in harnessing human energy is NURU Energy.[23]



While the overall climate for human-powered machinery seems to revolve around bringing power to the developed world, there is domestic interest to resurrect some of this "antiquated" technologies for domestic use. For example, Fender Blender offers a pedal-powered base, inspired by cruiser bicycle aesthetics, for use with a standard blender. Additionally, all of the plastic parts of the machine are made from recycled plastics. [24]

One success story of the implementation of human power, outside of the realm of pedal power is the treadle pump. [25]

Education for Sustain [26]

See also

  1. Barnes, D.F. and W.M. Floor, RURAL ENERGY IN DEVELOPING COUNTRIES: A Challenge for Economic Development1. Annual Review of Energy and the Environment, 1996. 21(1): p. 497-530.
  2. Fuller, R.J. and L. Aye, Human and animal power – The forgotten renewables. Renewable Energy, 2012. 48(0): p. 326-332.
  3. Starner, T. and J.A. Paradiso, Human Generated Power for Mobile Electronics. Low Power Electronics Design, 2004.
  4. Donelan, J.M., et al., Biomechanical Energy Harvesting: Generating Electricity During Walking with Minimal User Effort. Science, 2008. 319(5864): p. 807-810.
  5. Gonzalez, J.L., A. Rubio, and F. Moll, Human Powered Piezoelectric Batteries to Supply Power to Wearable Electronic Devices. International Journal of the Society of Materials Engineering for Resources, 2002. 10(1).
  6. Benkatraman, V. An electric workout through pedal power. The Christian Science Monitor, 2008.
  7. Czap, N., Stationary bike designed to create electricity, in San Francisco Gate2008: San Francisco, CA.
  8. Punch1895: London, United Kingdom.
  9. Mechtenberg, A.R., et al., Human power (HP) as a viable electricity portfolio option below 20 W/Capita. Energy for Sustainable Development, 2012. 16(2): p. 125-145.
  10. Modak, J.P., Human-Powered Flywheel Motor Concept, Design, Dynamics and Applications, 2007.
  11. Pedal Power, in Supplement to Energy for Rural Development1981, National Academy Press: Washington, D.C.
  12. Bhusal, P., A. Zahnd, and M. Eloholma, Replacing Fuel Based Lighting with Light Emitting Diodes in Developing Countries: Energy and Lighting in Rural Nepali Homes. Leukos, 2007. 3(4): p. 277-291.
  13. Chandler, L., Redesign of a Human Powered Battery Charger for Use in Mali, in Department of Mechanical Engineering2005, Massachusetts Institute of Technology: Cambridge, MA. p. 29.
  14. Cyders, T.J., Design of a Human-Powered Utility Vehicle for Developing Communities, in Department of Mechanical Engineering2008, Ohio University: Athens, OH.
  15. Raduta, R. and J. Vechakul, Bicilavadora, 2005, Massachusetts Institute of Technology: Cambridge, MA.
  16. Tiwari, P.S., et al., Pedal power for occupational activities: Effect of power output and pedalling rate on physiological responses. International Journal of Industrial Ergonomics, 2011. 41(3): p. 261-267.
  17. Dean, T., The Human-Powered Home2008, Gabriola Island, BC, Canada: New Society Publishers.
  18. Allen, J.S., In search of the massless flywheel. Human Power, 1991. 9(3).
  19. Butcher, D. Pedal Power Generator - Electricity from Exercise. 2012 12/16/2012 12/17/2012]; Available from:
  20. Weir, A., The Dynapod: A Pedal Power Unit, 1980, Volunteers in Technical Assistance: Mt. Rainier.
  21. One man dynapod, Uganda 1972, 1972, Alex Weir.
  22. Decker, K.D. Bike powered generators are not sustainable. Low-tech Magazine, 2011.
  23. NURU: Energy to Empower. POWERCycle 2012 [cited 2012 11/26/12]; Available from:
  24. Fender Blender. [cited 2012 12/12/12]; Available from:
  25. The Treadle Pump, 1991, Development Technology Unit, University of Warwick, Department of Engineering: Conventry, UK.
  26. Clarke, P., Education for Sustainability: Becoming Naturally Smart2012, New York, NY: Routledge. 140.

External links