# Converting human energy to electricity

#### MrSoftware

Joined Oct 29, 2013
2,117
There was a thread not too long ago about a hand crank generator, and part of the discussion was about how inefficient the conversion is, or how little electrical energy you get from human powered generators. Well, this popped up in front of me the other day and I can't think of a better example to sum it all up, and I thought it would be an interesting watch for many people:

#### Alec_t

Joined Sep 17, 2013
13,418
So, 0.021kWh used = 18 Calories.
One slice of toast contains ~75 Calories, so that should keep Robert going for a while .

#### mcgyvr

Joined Oct 15, 2009
5,394
This just proves that "Humans are basically powerless"

I bet he has trouble finding pants that fit without looking like M C Hammer 2 Legit to Quit..

#### Bernard

Joined Aug 7, 2008
5,784
He'll supply about one half of the energy required unless storage is involved ??

#### GopherT

Joined Nov 23, 2012
8,009
700W is just under 1HP. That guy is an Amazing athlete.

#### RichardO

Joined May 4, 2013
2,270
700W is just under 1HP. That guy is an Amazing athlete.
I remember a quote about Olympic track racer Nelson Vails having a "2 horsepower spring". Well, maybe he really did have that ability -- for very short intervals.

#### WBahn

Joined Mar 31, 2012
28,465
When I was in 8th grade we all measured our horsepower output by being timed as we ran up a tall flight of stairs (two stories in a string line). Mine came out at about 1.2 hp -- mostly because I was quite overweight and so my leg muscles had to be fairly strong just for everyday life and so they could put out quite a bit of power over the few seconds it took to climb the stairs. Had it been ten stories I image the average power output would have seriously tanked.

#### profbuxton

Joined Feb 21, 2014
421
Wasn't the Matrix powered by human energy? Not that it would be in any way efficient.

#### RichardO

Joined May 4, 2013
2,270
Helps to put this nonsense in perspective...

http://www.offgridquest.com/energy/an-hour-every-day-workout-can-power-your

This got monster traction on Facebook
"Having access to clean, free energy will enable poverty-stricken communities to not only light their homes but to connect to the internet and get educated. Bhargava says the reason the majority of those who are poor stay poor is because they have no power. He aims to fix this with the free energy bicycle."

Oviously food energy is free. What idiots.

#### WBahn

Joined Mar 31, 2012
28,465
So, 0.021kWh used = 18 Calories.
One slice of toast contains ~75 Calories, so that should keep Robert going for a while .
But that the amount of Calories of electrical energy he produced. What was the efficiency of the generator in converting mechanical energy to electrical energy? What was the efficiency of the bike in converting muscle energy to mechanical energy? What was the efficiency of his body in converting stored chemical energy into muscle energy? What was the efficiency of his body at converting food energy into stored energy? Even if we have just those four steps and even if they are all equally efficient (which, of course, they aren't), then that 75 Calories get chewed down to 18 Calories with an efficiency of 70%. Human efficiency in turning food into mechanical work is generally around 25%, so that right there completely accounts for the 75 Calories required to toast the bread. I'm not sure, but in most system the more intense the output the less efficient they are and I imagine human beings are no different, so a cyclist operating near their peak output is probably operating well below their peak efficiency. Any inefficiency in the mechanical/electrical chain just makes that worse. But those portions probably have pretty high overall efficiency.

#### joeyd999

Joined Jun 6, 2011
4,810
So, 0.021kWh used = 18 Calories.
One slice of toast contains ~75 Calories, so that should keep Robert going for a while .
Over unity with 57 calories to spare.

#### ktelectrician

Joined Jan 24, 2017
2
Really its very amazing Converting human energy to electricity.

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#### Alec_t

Joined Sep 17, 2013
13,418
so that right there completely accounts for the 75 Calories required to toast the bread.
It took 18 Calories to toast the bread (equivalent to the 0.021 kWh actually measured).

#### WBahn

Joined Mar 31, 2012
28,465
It took 18 Calories to toast the bread (equivalent to the 0.021 kWh actually measured).
Yes -- that is the electrical output that was actually measured. It is NOT the amount of food energy that needed to be consumed by the cyclist in order to produce that 18 Calories of electrical energy. The cyclist almost certainly burned more than 75 Calories of food in order to accomplish that.

#### joeyd999

Joined Jun 6, 2011
4,810
Yes -- that is the electrical output that was actually measured. It is NOT the amount of food energy that needed to be consumed by the cyclist in order to produce that 18 Calories of electrical energy. The cyclist almost certainly burned more than 75 Calories of food in order to accomplish that.

He was riding > 20MPH and weighs at least 185 lb. So, he was burning a minimum of 1,300 kcal/hr. or 21.6 kcal/min.

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#### WBahn

Joined Mar 31, 2012
28,465
I don't know how long he rode for, but about three or four minutes to toast a piece of bread doesn't seem too unreasonable. That is in rough agreement with an overall efficiency in the 25% range. I'd wager that he was putting out more than that at a lower efficiency, given how utterly exhausted he was at the end of the effort.

#### RichardO

Joined May 4, 2013
2,270
I don't know how long he rode for, but about three or four minutes to toast a piece of bread doesn't seem too unreasonable. That is in rough agreement with an overall efficiency in the 25% range. I'd wager that he was putting out more than that at a lower efficiency, given how utterly exhausted he was at the end of the effort.
... and that doesn't take into account the human energy used to plant, tend and harvest the "free" food. Never mind. He can't tend his crops since he is generating all of that "free" power.

Oh, and did you notice that the Olympic athlete wasn't reading a book or doing research on the Internet while toasting that slice of bread? He is such a slacker.

I will say it again about human power proponents. What idiots!!

p.s. I will add to this the fools that think they can get free energy by putting a generator in a backpack or shoes. Not only are you getting the energy conversion inefficiencies but you a wearing a backpack that rides like it is filled with rocks or shoes that feel like you are walking barefoot on cobble stones.

Why? Imagine for a moment that the padding in you backpack was perfect. No matter how much you jump up and down you would not feel the backpack. If you can't feel the backpack then you are not pushing against it to transfer energy. No energy transfer means no power generated. The only way to get motion to the backpack is to reduce the padding.

#### Tonyr1084

Joined Sep 24, 2015
7,353
Next test: Power a microwave oven. Boil a cup of water at sea level.

Water boils at 203.4˚F at my altitude, so higher would be easier. OR WOULD IT ? ? ? Less oxygen in the air.