Interresting that energy wise it is feasible to transport a whole lot of items that are not being used to the picker and back. But I am pretty sure that this has been taken into account when designing the size of the storage pods.
Pretty impressive!
I imagine that the cost of energy is minimal compared to the cost of labour in this case. But even if it wasn't, you still have 60-100kg people walking all over the FC so the difference in energy usage is minimal... but Amazon doesn't (directly) pay for the calories that their employees burn walking around the FC.
However one could imagine a Kiva v2 that figured out some way to not move whole racks at a time. The only reason they move the whole rack is to avoid having to build a robot that can pick individual items off of the shelf individually.
"We go around with a little cart to a conveyor belt and grab 2 plastic tubs. With a scanner in one hand and pushing the cart in the other your job is to go around to wherever the scanner tells you and "pick the items" This involves scanning the tub, then the location bar code, searching for the right item (which most of the time is easy to find but sometimes hard) and scanning it. Then doing the same thing for the next 10hours of your day minus the 2 15minute breaks and the 30min lunch break."
The people are just peripheral devices of the computer systems that run the distribution center.
Presumably they could make the stacks shorter and have more "floors" to increase efficiency of each trip.