# Do regenerative elevators exist?

**URL:** <https://boards.straightdope.com/t/do-regenerative-elevators-exist/304825>\
**Category:** Factual Questions\
**Created:** [May 21, 2005, 12:45am UTC](https://boards.straightdope.com/t/do-regenerative-elevators-exist/304825 "2005-05-21T00:45:52Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![OtakuLoki](https://avatars.discourse-cdn.com/v4/letter/o/ac8455/32.png) [@OtakuLoki](https://boards.straightdope.com/u/OtakuLoki)\
**Post date:** [May 21, 2005, 12:45am UTC](https://boards.straightdope.com/t/do-regenerative-elevators-exist/304825/1 "2005-05-21T00:45:52Z")

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I was just reading this [book](http://www.amazon.com/exec/obidos/tg/detail/-/0679734163/qid=1116636845/sr=8-1/ref=pd_csp_1/002-1840976-7052028?v=glance&s=books&n=507846). Anyone who’s interested in writing, SF, accidents, progress, technology, history of any of the above, or just plain likes reading will likely find it an interesting read.

Anyways, one of the ideas that sparked in my mind, while reading it, is, especially for multi-story office buildings and apartment buildings, realistically, over time the energy that the elevator’s motor adds to the things to be raised (in the form of potential energy) will be taken back from those same things - people, furniture, mail, etc. Why not use the braking effect that is being used to recover some of the kinetic energy of electric and hybrid cars during the braking phase to have loads being brought _down_ from a height contribute energy to the elevator’s motor?

Has anyone tried this and does it work?

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**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\
**Post date:** [May 21, 2005, 1:22am UTC](https://boards.straightdope.com/t/do-regenerative-elevators-exist/304825/2 "2005-05-21T01:22:51Z")

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Note that a lot of elevators use counterweights, cf. [this recent example](http://www.popularmechanics.com/science/extreme_machines/1280851.html?page=2&c=y). A typical counterweight system adds up to the car weight of 40% of the max load. (There are also hydraulic and other types.)

So if the elevator runs most often under 40% max load, it is actually gaining potential energy on the _down_ trip and losing it on the way up.

If the load is balanced, energy is lost mainly on starting and stopping the elevator + the usual friction losses.

Hydraulic systems are naturally “regenerative” if I understand the OP right.