Does anyway use escalators to generate electricty

[DTM]

I was at a large baseball stadium today and they had escalators to bring everyone up to the upper levels at the beginning of the game. At the end of the game, when everyone was leaving, the escalators were shut off and blocked off and everyone was walking down ramps to exit. I was thinking it should be possible to have everyone take the escalators down and the motors could be used as generators to generate electricity to sell back to the electric company. Does anyone do this? Is there a practical reason why this wouldn't work?

 

[rbelli1]

I would assume that under normal static powered off conditions the escalators would be designed so that even at full load no movement would occur. This would be a safety feature. If there is a power outage you don't want them to accelerate and injure anyone. In order to generate power you would need to maintain constant speed under some sort of electric and/or mechanical control. If that mechanism fails people die. See the accidents that plagued China for a while where the tracks came undone and thousands of pounds of people and machinery came crashing down.

BoB

 

[DTM]

Bob, Thanks for the response. Good points about the safety. I was thinking if you used a DC motor, battery and inverter, the speed would not need to be constant. You would also need to have an auxiliary brake to control the maximum speed. I'm thinking this could work very similar to how hybrid electric cars work, using the motors as generators to apply regenerative braking, but having additional brakes kick in when needed.

 

[rbelli1]

You need to control the speed for rider comfort. If you make it run normal speed during full load it will barely move with one person. Having it change speed mid ride would cause panic. I'm not saying you couldn't make it work but it would be unsafe.

With the hybrid design you will always get normal braking when pressing hard on the pedal. Industry standard automotive safety practices will apply. In a total power loss situation you will get a bog-standard un-assisted hydraulic brake.

I suppose you could design an emergency stop into to escalator but that adds cost and a point of failure.

Lets assume you have one 100kg person and they are at the top of a 10m escalator. The total energy you have available is 9.81kJ or 2.73Wh. Now you empty 100000 people from that arena. You have a total of 273kWh. At 100% efficiency you are talking about $20 of electricity. Probably a lot less at the rate that a stadium would get power but a ballpark estimate. You will get a lot less than 100%. Let's assume 50% (probably still very generous). Those 100000 people will be riding many escalators. Let's assume Shea stadium ratio of riders to escalators and you need 38 of them. Now you have about a quarter's worth of electricity. Your system needs to recoup its total cost over the lifetime of the device. Each game day it gives you a quarter. You will need to make your add-on fairly inexpensive or your power much more expensive to make this work.

BoB

 

[DTM]

Good calcs Bob. I hadn't bother to due the basic energy calculation, it just seemed like a lot of energy. The stadium I was at had about 30m of escalators, but still that's a puny amount of energy. Totally not worth the capital investment.
Dan

 

[rbelli1]

It might be economical if you could get everyone out on one escalator. However I don't think anyone would come back.

BoB

 

[Vanadium 50]

stadium would get power but a ballpark estimate

No pun intended?

 

[jim hardy]

An induction motor when driven by its mechanical "load" will return power to its source.
So what you propose should happen naturally.

Might be another reason though for shutting them off. A Bottleneck.
Is there another set of doors through which people must pass after exiting those escalators? If so, can people get out through those doors faster than the escalators can deliver them there? If not, you have an escalator-fed pileup right there at bottom of escalator.
People on a stairway can stop but on the escalator that's not an option.
I was once caught in such an escalator fed bottleneck pileup, was able to duck out a side exit before it got bad.

That's how the small things of the Earth confound the mighty.

 

[DTM]

I don't think there were any doors near the bottom of the escalators. But that would indeed present a danger.