Two elevators in side by side columns, their tops connected to each other via a chain over a pulley.
Such that when one is at the top the other is at ground.
Because the elevator cabins themselves are so heavy, a lot of energy is wasted in carrying them up and down.
If a pair of them could counterweight
each other, the actual energy spent will just be in moving the difference of their weights, which in the worst case equals the actual weight of people travelling.
In the best case, if the weight of people travelling down is the same as weight of people travelling up, will consume near-zero energy.
On days of normal routine traffic-pattern they would be constantly & alternately going up and down, making stops based on a simple algorithm in the contol panel.
On any floor whether you want to go up or down at least one of the elevators will be heading that way, which then stops to pick you up.
Of course the other elevator will also make an unnecessary stop , but the advantage of energy saved offsets that, I suppose.
Please comment, elaborate, question or enhance, any way you feel.
Thanks ---- Hemant@Sonawane.us