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I was interested in generating electricity using dynamo-electric generators when all external power sources are dysfunctional (power line fault, no wind, not enough sunlight, etc). Different bicycle part sites have varying info about how much energy their unique solutions can provide, and don't have any specific information, like voltage, watts, how fast and for how long you gotta step on the pedals and such. I suppose there should be simple formulas that allow to calculate all the important parameters.

Assuming we're interested only in conventional electric devices like 220v household electronics and 3v, 5v, 12v mobile devices, what is the average output of a bicycle generator being used by an adult for, let's say 15 minutes at the same speed? For how long would that support a 100W light bulb at full brightness, and approximately how long it could take to fully charge a completely discharged battery of a modern cellphone?

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  • Related to that, a typical bicycle dynamo generates 6V and 3W of alternating current. Sure wouldn't power a 100W lightbulb, but it still can charge phones and power some decent LED flashlights, although not both at the same time. If your needs are purely emergency reaction, that could be sufficient for some uses :)
    – aspyct
    Commented Apr 29, 2015 at 13:41
  • A 100W lightbulb is terrifyingly bright, though. If you used a more realistic 10W or 15W light you'd need much less pedalling.
    – Móż
    Commented Dec 17, 2015 at 2:02
  • Is this 100W light bulb we are talking about an old, inefficient incandescent light bulb or a new LED one? I would not call the former terrifyingly bright for, say, lighting a dining table, but the latter probably would be, though I have never seen such a strong one! (@Móż)
    – PJTraill
    Commented Dec 13, 2017 at 12:11

3 Answers 3

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It depends on what power you can produce and the efficiency of the equipment you use to convert that mechanical power into electrical power.

As a moderately fit 50+ cyclist, I can produce over 200 W for five or so hours, 300 W for much shorter periods, and levels around 1 kW for less than a minute.

A commonly quoted efficiency for electrical generation is 80%, but lets assume 75% efficiency to be just a little conservative.

200 W X .75 = 150 W

300 W X .75 = 225 W

If it's just for 15 minutes, we can take the higher figure. 15 minutes is .25 hours, so we have

225 W X .25 h = 56.25 Wh

So that would run a 100 W load for half an hour, provided the remaining parts of the system were 90% efficient.

Mobile phone battery capacities vary. Some are advertised at over 2000 mAh, and given a voltage of 3.7 V, that's

2 Ah X 3.7 V = 7.4 Wh

On these figures that 15 minutes of pedaling would charge a mobile phone seven times.

One limitation will be the efficiency of conversion of the electrical power from one voltage to another.

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  • 4
    charge rates are also limited - if you charged a cellphone for 15 minutes it would barely charge, but if you bypassed the charger and increased the charge rate the battery would probably explode.
    – Móż
    Commented Feb 22, 2016 at 4:15
  • @Móż An intermediate larger battery (with higher charge rate) or supercapacitor would solve this.
    – Technophile
    Commented Jul 30, 2021 at 3:25
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BBC1's "Bang Goes the Theory" demonstrated a human-powered home in a TK programme. In this segment, 8.5 kW of power required 70 cyclists, of fairly typical fitness, or about 107W per cyclist.

The full programme shows running a household of four for twelve hours utilising 80 cyclists, working with breaks.

The example isn't highlighting low-power draws, but does suggest that over a sustained period, about 100W is a good baseline assumption for power output of a human on a bicycle attached to a generator.

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  • But I still think that the second episode of Black Mirror was far-fetched
    – Sergey Zolotarev
    Commented Jul 28, 2021 at 9:40
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In 2015 Chris Froome during a Tour of France climb achieved an average of 414 W during a time period of 41 minutes.

I don't know how fit you are....

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    I'm afraid this doesn't answer the question, because clearly the OPs intent is to get some kind of average. Also I suspect that you didn't take conversion loses into account, but this is hard to verify because you didn't provide a source for your information.
    – THelper
    Commented Dec 13, 2017 at 12:44

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