[BULK] Re: harvesting energy

Hal Murray hmurray at megapathdsl.net
Thu Oct 27 19:16:32 EDT 2011

> Has anyone estimated the work required to charge an XO? Mike Lee gave a
> demo some time back at the Washington D.C. Learner's Club which seemed  to
> show that it would be a difficult workload for an adult athlete to  charge a
> laptop. 

You don't have to estimate.  It's easy to measure.

If you are interested in things like this, you should get something like a 
Kill-A-Watt.  They are down to $20 (plus shipping and such).
There are other similar units.

It takes about 20 watts to charge an XO-1.  Running uses 5 watts.  The 
backlight is a few more.  I think the limit is the front end so it will take 
longer to charge the battery if you are also using the XO.

If it takes 2 hours to charge the battery, that's 40 watt hours.

World class athletes can put out close to a horsepower for an hour or two.  
To do that, you have to use large muscles, so think legs rather than arms or 
hands.  (Bicycles are really good at extracting energy from a human.)

A horsepower is 746 watts.  That's enough bigger than 20 that I think it 
would be reasonable for a normal person to charge an XO from a well designed 
setup.  It will take a while.

It might be hard work for a small kid, or take longer if they can't generate 
enough power.



  A good cyclist could generate .4 horsepower indefinitely.

If you like human powered flight, Morton Grosser's Gossamer Odyssey is a good 
read.  It's got a section on how much power you can get from a human but I 
don't remember any details.

Bicyclists probably have lots of good data.


There is a guy in Silicon Valley who runs most of his house from solar and a 
bicycle.  He's got a stationary bike setup to feed power into his system.
He gets 24 watt hours from his morning workout.  He didn't say how long it 

More data from the same guy:

Here are some more numbers:
Scroll about 1/3 of the way down and there is a picture of an XO.  


There is an old joke/story about how to cure couch potatoes.  Setup their TV 
so it is powered from a stationary bike.  If they stop pedaling, the picture 
goes away.

I have a couple of friends with their displays and keyboards setup so they 
can use their PC from a treadmill.  It's a standard treadmill rather than a 
power generating setup.

These are my opinions, not necessarily my employer's.  I hate spam.

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