Jan 3rd 2017, 01:38 PM
Join Date: Jun 2010
Location: Naperville, IL USA
I'm not aware of anyone doing this, but I think it's less an issue of it being too difficult than it is an issue of not being economically practical. It seems like such an obvious thing, there must be a reason no one's doing it, and so ran a few back-of-the envelope numbers:
The energy that could be captured through a controlled descent of going down hill is:
Delta PE = mgh
If we assume the average person is 80 Kg and the height of the escalator is 50m then the energy that could be captured (if the machinery is 100% efficient) is
Delta PE = 80 kg x 9.8 m/s^2 x 50 m = 39,200 N-m = 39,200 watt-seconds.
If there were 10,000 attendees at the ball game, the total energy produced would be 3.92 x 10^8 watt-seconds. Which sounds like a lot, but convert to kilowatt-hours and it's only 109 kWh. The price of electricity varies, but a reasonable average number is 20 cents/KWh. So in theory the baseball stadium could sell the energy from one ball game for about ... $22. Obviously the investment for the special machinery to make this happen would be in the tens of thousands of dollars, so unfortunately this wouldn't pay off. That's why no one does it.