Ask the EcoGeek: Muscle Power
by EcoGeek.org 
on 07. 5.07
Instead of solar and wind power to supply to your own house - which are both weather dependent - has anyone thought about systems that might require some actual work, but provide a usable amount of power?
I was thinking, what if each member of my family carried a 40lb bag up 3 floors an hung it on a hook that was connected to a generator; would an effort like that actually provide a significant amount of energy? Just a thought.
Regards,
Jens, London
Oh Jens...you don't even know what you've done! Your question is totally a word problem from a physics exam. And as much as this will likely frighten most people reading this, I'm going to treat it as such.
If 120 lbs is lifted thirty feet and then allowed them to drop slowly over twelve hours, how much energy will be produced?
120 lbs * 30 ft = 3600 ft/lbs = 4880 joules = 1.356 watt hours / 12 hours = 0.113 watts.
So, in answer to your question, no, that would not provide a significant amount of electricity. In fact, in order to power one 60 watt equivalent CFL for twelve hours, each member of your family would have to march up the stairs about ten times.
But that doesn't mean that you don't have an excellent point. Every person is a magical little energy factory. Whataburgers go in...watt hours come out, and it is possible to harness that energy.
Some schemes in converting muscle power to electric power even seem pretty intelligent. A gym in Hong Kong has hooked its treadmills to a battery bank, using the energy of its clients to power the lights. A subway in Japan harnesses the energy used by people walking through turnstiles to power lights. And we've all seen various gadgets that can be shaken, squeezed, cranked or yanked to generate the juice that makes them work.
But a more personal and powerful option for a muscle-powered home is a pedal generator. Basically, it's just your average exercise bike, except there's a generator on the inside. The maximum output for a toned adult would be about 500 watts, but a sustainable level for someone like me (who's eaten his share of Whataburgers) is more like 150 watts. Amazingly, this would be enough to power both of my laptops, two CFL light bulbs and my cell phone charger for as long as I kept pedaling.
There are two problems though. First, no one can pedal forever. And second, they're not yet selling pedal generators at your local hardware store. But if you can get your hands on one, like the $230 pedal-a-watt bike-to-generator conversion kit, you could easily lower your electric bills, or charge an emergency backup battery, and become a healthier EcoGeek at the same time.
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every office building should only have rotating doors in the front so everyone who passes through them will be helping to power that building.
but if you're looking for exercise, surely using your pedal power for transportation is the more efficient way to go, no?
When I put my Whataburgers towards getting me to work every morning, it lets me avoid operating an enourmous, polluting hunk of metal and toxic materials. When you pedal for this fraction of your home electricity use, you're not able to kill a power plant as a result as you're not generating enough to take your home off-grid.
The real advantage lies in flipping the math you just did. While 0.113 watts of electrical energy is not worth much to us, we frequently use electricity to reduce physical effort.
Doing physical tasks physically rather than using electricity can save useful amounts of electricity. Push mowers, transportation, cleaning by hand treadle sewing machines, and treadle anything are all great examples of technologies that use human energy to do useful things.
Add to this the increased energy and health that comes from physical work and yes human energy is a great alternative to electrical energy.
No, you won't be able to remove yourself from the grid with pedal power alone. But, if this means of generation we're taken to the next level, and consumers we're able to combine this into their home energy, as solar panels augment out use, then this would be a great way for additional power. This assumes that in the next ten years solar, wind, and morning cycle power would feed into a home battery bank.
What if you threw gears and/or flywheels into the equation??
I think they used to call it Elbow Grease...
I think there's a gym in LA which also uses the bikes to power the lights, a bit like the gym in Hong Kong. Not sure how the treadmills work though as they move whether you're on them or not - you're not actually moving with resistance it like with the bikes.
I think the problem with the rotating door and some other suggestions for harnessing power is that the copper and magnets used to make generators and motors are a semi-limited resource. It seems like by the time we made enough small scale generators to really make a difference we would have seriously impacted the cost of large scale wind farms and electric cars.
Also, every time you convert energy from one form to another, you get loss. For example, translating mechanical to electrical to mechanical (ie ride a bike generator to charge a battery to power a blender) causes huge losses. So look for ways you can simply translate mechanical to mechanical. (Using a hand-powered grinder or ricer instead of a blender.)
This is an extreme example, but it leads to ideas. Why not a refrigerator where the compressor gets its energy not from an electric motor run by a pedal generator, but rather the bicycle runs the compressor shaft directly?
I was just thinking of this the other day at the gym. All those bicycles burning only calories. If they could at least power the TV's and fans, or those tanning booths!