How Much Electricity Can You Generate Using a Pedal-Powered Generator?

Several years ago, I took part in an exercise study that measured the effect of a nutritional supplement on human performance. As part of that study, the investigators measured my peak power output while pedaling a stationary bike. It was over 300 watts.

And yet, when I'm pedaling a generator while working on my computer, I'm only able to generate about 50 W of electricity on average. Why is it so much lower?

There are multiple factors that influence how much electricity you can generate using a pedal-powered generator. Some are biological, some depend on the design of your generator. Let's look at them one-by-one.

Biological Factors

Duration

Your power output depends on how long your exert yourself. Over short time periods, your power output can be quite high--healthy young men can produce several hundred watts for up to a minute or two!

But the length of time you can exert yourself at such a high level is limited.
Your body gets it energy by breaking down the glycogen stored in your muscles. When exercising hard, your body cannot consume enough oxygen to fully meet its needs. As a consequence, your body breaks down the glycogen anaerobically (i.e., without oxygen), producing lactate as a byproduct. The lactate builds up in your muscles and causes a painful burning sensation, forcing you to stop exerting yourself so hard.

During longer, less intense periods of exercise, your body uses oxygen to breakdown glycogen and fats for energy. This aerobic ("with oxygen") metabolism does not produce lactic acid, so you don't feel as fatigued. However, the amount of power you can sustain is only about 25-35% of what you can produce anaerobically.

If you plot your average power output over different time periods, you'll get the following graph:

plot of human power output as a function of time during cycling
Human power output as a function of time during cycling (taken from Limits to sustainable muscle performance: interaction between glycolysis and oxidative phosphorylation)

The horizontal portion of this graph is the region you'll spend most of your time pedaling and generating electricity. I call it your sustainable power output level. It's the amount of power you can produce regardless of how long you pedal.

Fitness Level

Your sustainable power output depends on your fitness level. Some elite athletes can maintain 350 W or more for more than 30 minutes. A fit recreational cyclist, you can probably maintain about 200 W, while the average, untrained person can produce about 75 W.

Fitness Level Average Power Output
(> 30 min)
average, untrained person 75 W
"fit" recreational cyclist 200 W
elite cyclist 350 W

It should be noted that your fitness level responds to training. The more you exercise, the higher your sustainable output will become. This mean your average average power output will usually grow the more time you spend pedaling and generating your own electricity.

Age and Gender

Your power output also depends on your age and gender. It increases up to about age 20, plateaus until you're about 35, gradually declines to about age 50-60, then declines more rapidly after that. This is only a general rule, however; for elite athletes, power output appears to decreases gradually age 20:

plot showing how power output declines over time for both males and females
Power output of female (top) and male (bottom) of different ages of some elite cyclists, showing differences in power production by age and gender. From J Sports Sci Med. 2007 Dec; 6(4): 477–483.

Men, in general, can produce a little more power than women, due to the fact that men on average have more muscle mass than women.

Multitasking Ability

Using a pedal-powered generator with a bike desk is different from using one with a stationary bike. On a stationary bike, you often have nothing else to do but look at it's display and watch your RPM or total calories burned. As a result, you tend to ride hard to maximize those numbers.

When you're using a bike desk, you're focused on what you're trying to accomplish on your computer. The exercise benefit is secondary.

It's hard to sustain a high power output when you're focused on some other task. When you focus on your task, your power output tends to fall. If you shift your focus to maintaining a high power output, your ability to concentrate on the task declines, and you become less productive.

Based on my experience and those who have used my machine, along with researchers I have consulted with, the maximum power someone can sustain while engaged in a task is about 50-60 W. Anything above that amount will cause you to be significantly less productive in the task you're doing.

Environmental Temperature

Pedaling in a stationary position at room temperature will make you uncomfortably sweaty after a few minutes, unless you limit your power output by pedaling more slowly or take some other measures to keep cool.

Some of those measures may include:

  1. work in a cool room,
  2. wear cooler clothing (like shorts and a t-shirt), and/or
  3. use a fan

I find myself usually using needing to use a fan. If you plan to power it using the electricity you create like I do, you'll need to subtract it's power consumption from your power output. My small 12 V DC fan consumes about 5 W of electricity, which is typical for a fan this size. So, if your using a fan while producing 50 W of electricity, your useable amount of electricity will be about 5 W less, or 45 W.

If you work in an office environment where you can't control the room temperature, wear cooler clothing, or use a fan, your maximum power output will probably be much less--about 30-40 W--to keep from perspiring excessively.

Generator Efficiency

So far, we've assumed that all the power your body produces is converted to electricity. However, that is not true--pedal-powered generators are not 100% efficient at converting your power output into electricity. Some power is lost through the gears, chain(s), or belt(s) that drive the generator. Even more is lost converting the rotation of the generator shaft into useable electricity. A final loss occurs in any post-generator conversion, like converting DC electricity to AC. The overall efficiency of a pedal-powered generator is usually at best around 80%.

Conclusion

The amount of electricity you can generate using a pedal-powered generator depends on a number of biological factors, like your age and fitness level, as well as the efficiency of the generator you are using. An average person capable of producing a sustained power output of 75 W can expect to generate from 30 to 60 W, depending on the efficiency of the generator system and environmental conditions.

That may not sound like much, but it's enough to completely power a home office (if you have the choose the right equipment) while burning a significant amount of calories. I'll cover those topics later.

written by
Jim Gregory (contact)
published
2018-03-19


RSS feed