Like millions of Americans, I use machines in the gym that turn a wheel of one sort of another. And like many others bored to tears while working out, I wonder why all that the human energy exerted on a tread mill or elliptical trainer couldn't be converted into electricity.
To a small extent, the machines I use already produce electricity. At my Planet Fitness, the TV channel changer and volume affixed to the machine runs off the exertion of the user. But that module draws milliamps.
What about harvesting the human toil for the gym's lights, HVAC and TVs?
But it might not be worth much more than a green feel good proposition: the school estimates if 3,000 people a day used the machines, the yield would only be 6,000 kilowatt hours (kWh) or enough to supply my home for about 8-9 months.
That's measly production for $14,000 worth of retrofitting! At what I shell out for residential electricity, payback at the implausible maximum output of electricity wouldn't be at least for 17 years!
I was surprised not only by the small amount of electricity, but the required usage. Twenty machines in non-stop use with each person taking 15 minutes amounts to 1,920 persons a day. Number of people sounds like a fishy calculation.
Why not just say all 20 machines must be used 7x24 to produce 6,000 kWhs? Factor in breakdowns and people getting off and on the machines, true 7x24 use is probably impossible.
The generating equipment comes from a Florida company named ReRev, which boasts about a dozen mostly college and university customers. ReRev's rule of thumb metric is a bit more understandable: a 30-minute workout produces about 50 watts or enough to power a light bulb. Another ReRev metric is that an elliptical trainer in regular use over two days produces one kilowatt hour (1,000 watts produced for an hour).
"ReRev™ retrofits cardio equipment to reroute the energy that is being emitted as a heat by-product. Instead of the equipment raising temperatures inside the facility, causing the air conditioning units to work harder, the energy is delivered to a central processing unit which converts the human power to utility grade electricity. Each retrofit has a controller box which feeds back through a processor and into a central-grid tied inverter, tapping directly into the building’s electrical system -- creating free electricity with no maintenance required" according to ReRev's web site.
Even if the economics don't work, I like the idea of capturing physical energy. It gives one insight into how much power we use everyday and of course, the electricity is carbon free. For a place like my gym, such power-producing machines would also be a sign-up enticement for new customers who want to be greener.