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Powering the World, One Gym at a Time

My blog handle is "The Mathlete" because in addition to physics, I love working out, often to the point of obsession.  Recently we've had a lot of rain here and I've been inside in the gym running on the treadmill and using the stationary bikes (aka torture devices).  I'm sure everyone that has been in a gym has at one point thought that it might be a good idea to take the power people are generating from using these machines and using it to power their house.  Two groups have decided to do just that, use the power from the exercise machines to power parks and houses.  A group in the UK recently created an outdoor gym that uses the workout equipment to light the park lights and a homeless shelter in Detroit has built a "green gym" that recycles the energy back into the power grid.  But how efficient is this type of power really?  Could hooking up every exercise bike to the power grid save our energy crisis? 

The Cass Green Gym for the homeless boasts that if they have 4 hour-long classes a day on their 10 exercise bikes for a year they could power 36 houses for a month each.  Now, the irony of having homeless people power homes is not lost on me.  Frankly, this reminds me slightly of The Matrix and using people for batteries.  But, I couldn't resist a Fermi problem like this.

40 bike-hours a day for a year would power 36 homes for a month.  That means that roughly the power produced by one person in a year of evil spin classes would power a house for a month.  It would take 12 people toiling away for an hour a day on a bike to power a house for a year.

There are roughly 100 million occupied homes according to the US Census Bureau .  That means that to power those homes for one month would take 100 million bike-hours a day for a year to power all those homes for a month.  To power all US houses for a year would take over a billion people peddling an hour a day for a year.

But what could we do with the power produced by people that already workout?  About 45 million people own gym memberships yet only 33% of people use them.  That would mean that about 15 million people use the gym in the US.  Assuming "using the gym" means that you go for an hour a day as recommended by the CDC this would mean that the US is working out for around 15 million hours a day.  If we make the grand assumption that every one of these people is riding an exercise bike for that hour (which would be horrible) that would mean that 15 million homes could be powered for a month, or around 1 million could be powered for a year.

Honestly, that's not too shabby.  Maybe we should look into this, at least we would be getting something out of those horrible hours and painful chaffing.  I think next we should talk about hamsters and wheels....


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