Energy-Generating Floors to Power Tokyo Subways
Energy-Generating Floors to Power Tokyo Subways
Old, but I just came across it, so it's interesting to me.
The numbers don't make any sense.
A 100kg (220 lb) person whose steps compress the tiles by 1cm (0.01m) per step would be transferring 100 kg x 9.8 m/s^2 x 0.01m = 9.8 joules, or 0.00272 watt hours. That assumes 100% perfect efficiency in capturing that energy.
A watt is a joule per second, so someone who steps 1 step per second is generating 9.8 watts. That's not enough to light the station, much less run the computers and signs and the fare gates and escalators and elevators.
And of course it wouldn't come anywhere close to running the trains. After all, if it were easy to take people's biomechanical power to run trains, that would mean that humans could push the trains effectively.
Certainly you're right about the computers and gates and trains. But 9.8 watts per occupant may be enough to light the station when it's in use.
So even with those ultra unrealistic assumptions (100kg people, 1 step per second, 100% efficient energy capture), 9.8 watts just isn't enough.
Lighting needs about 0.6 watts per square foot (6.46 watts per square meter) in an office. That means you need someone like that generating 9.8 watts every 16.3 square feet or 1.5 square meters.
There's an inherent tension there, where sufficient density to make that work would require people to take fewer, shorter steps.
A basketball court is 4700 sq feet (436.6 sq meters). That means you'd need 288 big people stepping that fast, jammed into a single basketball court sized space, just to keep the lights on in that space. If any of the people stop moving even for a second, the system fails to keep up.