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Mr. S.


As for energy storage, wouldn't making the pedal-powered machine actuate a vertical water-pump be ideal? No electronics, or chemical battery, and when power is needed water can be released from a water tower to generate current with some kind of turbine. Better yet, a windmill could be the primary power for the pump, with pedal power as a fallback for long windless periods.

Kris De Decker


Sounds like an interesting concept to me. But, the question is how big that tower has to be, and how much energy it takes to build it.

charley hardman


love this article. have long been fascinated by human power, and would like to live in a human-powered home. my vague design centers on several transmission methods (e.g., bicycle, fitness machines), all connected to a lifting a large weight that may be lowered on demand for electricity or straight mechanical power. similar to Mr. S's description with water (as used regularly for time-shifting hydroelectric power).

of course, a unilateral human-powered home requires radical changes in HVAC, mostly centering on acclimation and localization (e.g., electric clothes).



I had plans drawn out for a while now around the concept Mr. S explains. Many well designed off grid homes use elevated water so that they still have running water available, but they rely on using a generator once in a while to push the water. I always thought a small windmill could do the work of lifting the water into a small tank, and when electricity is desired, then this essentially turns into a microhydro system as water empties from the tank while spinning a series of turbines as it falls.

Kris, it's nearly pointless to question the energy required to build this type of system. It's obviously considerably less energy both upfront and continuing versus being grid tied (relying on miles of copper) and coal/nuclear/gas providing that power.

Colin Tonks


Hi Kris, this is an interesting piece of work and well put together. I especially enjoyed reading the history of the pedal powered machines.

Furthermore, I absolutely agree with you that humans generating energy, with a bicycle, is completely inefficient. In fact, the cost of the food required to pedal would be 150 times more expensive than the cost of buying the energy direct from a local supplier. So what is the point and why do we do this?

Well, there is one important point that I would like to make and that is the indirect benefits of this approach when applied in an educational environment. We’ve done hundreds of events using the technique of people generating their own electrical energy and then using it to do something fun. It does not matter if it's a festival, school, corporate etc., we get the same reaction every time .. a new found appreciation for energy.

For many people, pedalling to boil a kettle of water or even lighting a light bulb is ‘enlightening’, it's that relationship between what they are feeling in their body, the burning their muscles, the excitement of being in control to bring alive an electrical appliance that is stimulating and thought provoking.

I'm not saying that people who generate their our energy go away and become eco warrior and start wear heap shoes, it's more of a subtle push in the right direction, a small step change in behaviour that would hopefully lead to a more sustainable existence. Thanks Colin

Kris De Decker


@ Andy: I am interested to know more about the plans you drew out. Some time ago a reader asked if there existed something like 'micro hydro pumped storage' because he wanted to be fully energy independent without using a battery. He had asked an architect to design such a system but the architect just laughed and walked away.

So I made a calculation myself and concluded that you need quite some spectacular reservoir if you want to have a pumped storage for your house, even if you use considerably less energy than the average household. (I lost the calculations, unfortunately). I guess it's not only a matter of embodied energy (a water tower can last for decades, so indeed this might not be such a problem), but also of space. It would be great to hear more ideas on this topic.

@ Colin: I support what you are doing and I am convinced that your projects do have a positive effect on people's behaviour. And if I got it right, you did not use batteries for the BBC TV series? I think it's obvious that I am a supporter of pedal powered energy, including generating electricity for devices that can't be driven mechanically, but we have to find a way to do away with the batteries, because they destroy the whole concept from an ecological/efficiency viewpoint.

charley hardman


i approach the efficiency topic from the other side. i loathe "working out", lifting weights only to lower them. would like that converted into useful power along with the physical benefit. any true analysis must include wasteful expenditure of the subject that might be converted. caloric analysis must at least also subtract normal spending for mere existence (e.g., sitting in a chair reading book).

i suspect the most practical local solution is hydraulic power transmission (i.e., high pressure, little movement) to a dense mass (e.g., lead). don't think water will cut it as per-home kinetic energy storage medium.

Chris Vernon


I've tinkered with bicycle electricity generation, thanks for this fascinating article.

Regarding the 10 to 35 percent lose in the battery and 5 to 15 percent loss in the DC/AC converter, for many applications an ultra-capacitor can be used to maintain/smooth the voltage and of course we should only be using DC loads! No point it going anywhere near AC. These two points improve the efficiency quite a bit, but fundamentally, I agree with your conclusions we should be powering devices mechanically.



A brilliant article, as they always are, but...

You say "An energy loss of 42 to 67.5 percent of naturally means that it takes 42 to 67.5 percent more effort"

Wrong maths! Say you had a 90% loss, you'd need to provide 10 times as much energy to get the same result. Or 900% more.

So a 67.5% loss means 100/(100-67.5)*100 = 3.07 times as much input energy is required, or 307% as the original, or 207% extra input energy.



I've been playing with the idea of using a bike and alternator to power an electric water heater. The electronics aren't necessary then and alternators can come from junkyards for $35 or so. An RV 12-volt heating element costs less than $100. Any old water heater should work.

Of course, I don't have a working prototype running yet. But I'm fairly close and the process hasn't been particularly difficult so far.

Michael Dawson


Has anybody applied this kind of analysis to the so-called electric car? Where could one find that?

Kris De Decker


@ Adrian (#9): You must be right. I will correct it. Math is such a weird thing: I made a mistake in the calculations but the end result was correct...

@ Mike (#10): Interesting idea. Generating electricity to produce heat is considered to be very inefficient, but using the water as a battery at least makes the whole system sustainable. I think the only downside is that you will have to pedal a lot to take a hot shower.

Kris De Decker


@ Michael (#11): I made a calculation of the embodied energy of an electric car battery here (about halfway the article):

It was a rough calculation because of the few sources available, and meanwhile another study appeared which arrived to figures which are about half as low: http://pubs.acs.org/doi/full/10.1021/es903729a

It should be noted that this research paper was sponsored by a Swiss electricity producer and a lithium mining company (see the last paragraph). I guess we would be somewhat suspicious when a research paper sponsored by the oil industry concluded that gasoline powered cars are better for the environment than electric cars... Anyways, the embodied energy of batteries definitely makes electric cars less sustainable than is generally assumed.

And what about solar panels + battery? One of the sources I refer to concerning the embodied energy of a battery, talks about solar panels connected to batteries in an off-grid system. From their numbers it can be concluded that in less sunny regions the energy payback time is longer than the life expectancy of the solar panels. Without batteries, energy payback time is positive. See the discussion here: http://www.lowtechmagazine.com/2008/03/the-ugly-side-o.html?cid=6a00e0099229e888330120a69d6a05970c#comment-6a00e0099229e888330120a69d6a05970c

jason crowther


in order to re-gain the strength i lost due to head-injury, i spent much time on a rowing egometer. the appartus included a monitor measuring various outputs during a workout. eventually, i reached 46,400 watts/41 minutes. of course, these measurerments increased as my strength and endurance increased. i remember thinking that--maybe--i was onto something! could i use this system to increase my income through selling the power back to a local provider?



The assertion that "An energy loss of 42 to 67.5 percent of naturally means that it takes 42 to 67.5 percent more effort or time to power a device (say, a blender) via electricity compared to powering the same device mechanically" has a math error. The numbers to use are 1/(1-.42) at the low end and 1/(1-.675) at the high end. So you'd actually need 1.724 to 3.077 times more energy to compensate for a lost off between 42 to 67.5 percent.



To the author: I am a cyclist and I need to train indoors occasionally. I am thinking of finding a used DC generator and AC converter to run with my road bike. I understand that there is quite a bit of energy loss, if I try to store it. But could I just plug the AC current into my wall socket to slow or run my meter backward? I need to do the work out anyway, might as well do something with the energy.
Your response would be appreciated.

Michael Boswell


The advantage of simple pedal power is that almost all humans have legs and can generate power small machines. The best Australian example is the pedal wireless. This simple invention provided communications to regions of Australian were electricity supplies were non-existant. Which prior to World War 2, was most of the Australian land mass. Naturally, this two way radio service was public but no one ever listen to another conversation. Well, not much!

The other useful thing for human power machines is for things like sowing machines. I have heard many old ladies bemaon the disappearance of the old 'pedal sowing machines". One control was the amount of power that you put into the machine. Electric ones have other means to vary power but one cannot feel the power going into it.

This is my first time here and I am subscribing.



I am interested in the use of pedal power while people are driving to generate electricity; though ineffecient, if a person is idle and not able to use time more efficiently any other way, this is a use of energy that otherwise cannot be used otherwise. Use of pedal power to charge batteries for use of power either in vehicle or for other purposes - and get needed exercise for our sedentary culture.



I've been intrigued by this "people power" concept for a few years. I don't have any technical knowledge of how this works. It seems to me there should be some way to use human activity to generate power or to power devices in some way. There are some indirect benefits in the form of more exercise, particularly for combating obesity including childhood obesity. If there's a people-powered device in every home, perhaps families could generate enough electricity to watch TV or charge their cellphones, etc. Parents could make sure their kids participate in generating enough power for the family to watch a program or play a video game. It could be a trade off: Sure you can play that video game, but you need to do some pedaling to make it happen! That kind of thing. It may not be efficient energy production but it has side benefits. Another application would be for emergencies, say when a hurricane knocks out power to your house. A bicycle-powered device could help pump out excess water from the basement, sound an alarm, provide lighting, or charge cellphones for emergency phone calls, etc. All things considered, it would seem that this concept has some potential, especially if you consider that millions of people drive to a fitness center (using energy to manufacture and power the car) and then turn on various electricity-driven exercise devices (like treadmills). Why not encourage energy production and/or create practical devices that are driven by human exercise in homes or at green fitness centers? There may be efficiency breakthroughs the more scientists and engineers explore how best to generate and harness energy produced by "people power."



If you make an electricity generating device (I built a rowing machine) from scrap materials (- I got a usable battery from the scrapyard also) then the energy that has been put into making those parts is history you can't change that but by using those parts to make electricity at least you are recouping some of it and balancing things in a positive direction overall

jane hansen


I am looking for the best way to use "human power" to run a sump pump in the event of a prolonged power outage. I had thought to use a bicycle to charge the back up battery...but may be there is a better way. Got ideas anyone???

Jane H.
Barrington, IL

Brian Hansen


Jane (#21): I think one message from this article is that using direct rotational energy is hard to beat for efficiency. From an engineering perspective this may be a principle in search of an application. When I think of a sump pump, I think of it as being asynchronous, running only when needed, for as long as needed. That scenario would suggest stored energy to run the pump.

It is possible, though, that it could be routinized, or perhaps scheduled, such that an individual could "ride" for 10 minutes every 6 hours, for instance. Or "ride" as long as needed when an alarm went off.

A direct mechanical linkage would present its own problems, of course. The bike has to be next to the pump.

Kris De Decker


@ Brian: "The bike has to be next to the pump."

Unless you use a jerker line system: http://www.lowtechmagazine.com/2013/02/the-mechanical-transmission-of-power-jerker-line-systems.html

Ssempa Nelson


The author is forgetting that by using a pedal generator, many liters of paraffin is not being used, reducing on carbon emission and also preventing the inhaling of the carbon by the people who use paraffin candles. Also measure the impact of using hydro power and the power generated by pedaling. If this is introduced in our developing countries many young children who read using candles will have a chance to access safe lights.



Interesting article. I'd be interested in a stationary pedal generator. My purpose would be to power radio equipment in the field. If I was to run it without a battery, I would need a flywheel to handle the transmitter's peak power (100W PEP, or 250+W on peaks) for SSB transmission. This would be an ugly load to handle directly, so using a flywheel would make it easier to pedal. Would still need DC voltage regulation, but modern switchmode regulators can exceed 90% efficiency.

A more likely scenario is to augment my existing solar system, which provides 100W into a battery. Pedal power could be used when sustained power levels near or exceeding 100W are required, or at night/under cloud to keep the battery topped up. It' also a way to maintain aerobic fitness while doing other things I enjoy. I am also a regular cyclist in the conventional sense (i.e. transport).

Obviously for my application, using direct mechanical transmission is not an option! :)

Steven Miller


The author brings up many good points all of which should be considered when designing pedal powered devices. I have tinkered a great deal over the years with human powered devices. Most of the inefiencies mentioned in the article can be reduced greatly by various means.

Obviously, a gallon of gasoline, ten pounds of coal or a small stack of firewood contains far more energy than a person could produce in days. The United States currently has 1.5 million pounds of proved accessible coal reserves for every person currently living in the country, billions of gallons of proved accessible oil reserves, and multiple trillions of cubic feet of proved accessible natural gas reserves. So for day to day energy needs there is only the slightest possibility that we are going to rely on humans for large scale power generation during any of our lifetimes.

However for emergency situations or inaccessible locations many modern electronic devices are efficient enough that several at a time can easily powered by one person with pedals or even hand cranks. I have several generations of hand cranked generators from early telephone magnetos to generators designed to power radios in WWII and up to Chinese military generators built in just the last decade. I also have built a permanent magnet based pedal powered generator that is extremely efficient that uses nothing but chain, sprockets an internal gear motor and a flywheel to spin the generator at the most efficient speed for power generation. It is mounted on an upright exercise bicycle. This can be used for producing power of up to approximately 180 watts at 12v DC continuously depending on the fitness level of the person at the pedals. This can directly power small electric motors with very little loss or to charge batteries. Unfortunately, I doubt whether there would be enough demand for this device at this time to justify production.

The author brings up many of the challenges that face designers of human powered devices, but his conclusions tend to lead one to believe that they will never be useful. To me this seems to be a short sighted argument that can be shown to be invalid by just one valid application. Human powered generation devices have been used in communications equipment for over 100 years. Just because the author does not know of a good use for such a device in his life does not mean that others do not have useful applications.

tom foxe


People are perfectly happy to use lots of energy running, cycling or dancing just for fun or to keep fit.
It's true bike power is not efficient, but neither is a centralised power grid which uses up most of the power generated to heat the cable network.
I run a pedal-power sound system and people just love it. I don't tell anybody that it's a substitute for mains electricity.
I'd rather read what pedal-power is GOOD for. I already know its limitations.



Very interested in this article. However, calling human power inefficient is puzzling to anyone at the gym watching the meters. I was lamenting how efficient we are. It's a real challenge to burn off that $0.70 Snickers bar on the stationary bike. Also, I think it is an uneven comparison from generating instant use mechanical energy to battery stored electrical energy. Batteries have nothing to do with generating electricity, only storing it.

Sho Me


This is an interesting assessment of power loss in human powered electric generation, but the fundamental assumption that bike powered electricity generators are not sustainable is flawed. The flaw derives from a missing definition for "sustaintable." None of our lives are sustainable. We will all be gone within most likely, at most 12 decades after our birth. Life on earth is most likely doomed to extinction sometime within the next billion years as the sun increases light output, because the sun itself is not a sustainable system.

Faults cited in the measure of undefined sustainability include the fact that it "takes energy to manufacture a pedal powered machine that does not take the intermediate step of generating electricity. This concern lies mainly with the production of steel."

Again, nothing in modern human culture is sustainable by that measure. Metals are part of every "sustainable" system proposed by modern green culture. Even those sustainable hemp grocery bags are woven on automated metal machines from hemp harvested with energy intensive metal tractors.

Even if were were to prefer a culture based on products made only from annual plants, the culture to preserve tenure to that land is not sustainable until all peoples anywhere in the world - and maybe even the animals - agree to a unified system of land holding. That is sustainable only in one place - in your dreams. And your dreams are not sustainable because (I borrowed this line from Zimmy) you've got some big dreams baby but in order to dream you've got to still be asleep. When you gonna wake up?

That said, the article is an interesting study of an interesting idea. Two places pedal powered electricity might be practical - in terms of modern culture - would be in exercise machinery and in low-powered living, either long term or in temporary settings. For exercise bikes, I would as soon generate electricity for my laptop - which generally uses less than 60 watts, which I can generate from the approximately 100 watts I produce sitting on a trainer.

Likewise, in a low-power living arrangement - maybe off the grid no matter what my motivation (sustainable?, aesthetic?, lux camping?, socio-political isolation?) I can use a bicycle generator to charge electronic devices, supplementing other power sources including solar or wind.

Overall, I agree the limitations of pedal powered electricity make it impractical. Friends have tried various setups in their off-the-grid homes and quickly given up. But the advent of new, affordable portable high-density batteries and the proliferation of portable electronic devices - including cameras, tablets and especially low-power LED lighting - have brought new possibilities for pedal powered electric generation



What about pneumatics? How about using some pedal powered device to compress air in an air tank, and then use use the compressed air to drive tools or a motor.



First, thanks for the reminder on flywheels. Having been ignored for obvious reasons by all and sundry in the UK I recently decided to use a bicycle generation arrangement to demonstrate what I found back in 2009. The article is spot-on in explaining the inefficiencies but that is the area in which I’ve been working. The term “counter torque” is not mentioned, but most of the angst of human-powered devices could be directed at that one term. Many will know this, but the increase in applied force required as the electrical load increases is due to the magnetic effect that the generator stator has on the rotor. I’ve found a way of duplicating that effect in reverse which, of course, changes the playing field entirely. Regards, @withthechange.



I think the term "sustainability" should be more rigorously bond to scientific connotations. This article does not make sense in this regard: of course takes energy to build any sort of things!
By the same token many anti-environmentalists (eventually backed by oil companies) declare solar power not sustainable. Sure it takes energy to produce solar panels or to build a human powered generator, but then they work out of free solar energy or human sweating!
Stating human powered generators are not sustainable is unbelievably wrong! The author maybe prefers nuclear, burning down Amazonia forest or oil burning? Really?

On the engineering side, I am happy to announce that the above mentioned efficiency losses have been reduced by a great amount in the last century, i.e. a DC-DC converter with above 95% efficiency fits on a finger tip and costs few dollars!
Besides, modern cars and in general internal combustion engines' efficiency is far less than 50%. So what? Let's dump it and get back riding horses?

Power losses in state-of-the-art turbines for energy production are comparable with the numbers stated in the article, plus they burn oil or gas, producing combustion gases which are not the best thing ever in terms of sustainability. Also these plants use tons of fresh water in the cycle.
I guess for comparable efficiency, at the very least the wastes of a cyclist are by far more eco friendly and sustainable than the ones from production plants!

In conclusion, the article goes quite deeply into explaining technical issues related to human power generation systems but on the minus side, the conclusions are not realistic as they rely on not updated data, math is flawed somewhere and the concept of sustainability here stated is remarkably misunderstood.
Furthermore, before declaring pedal energy not sustainable, the author should have at least mentioned and compared it to actual production systems in order to provide a thorough analysis.

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