Not sure where to ask, /sci/inteists, but is there any way to harness energy from a change in altitude?
E.g. if a helicopter goes up to an altitude of 2000 feet and then down again and repeats, is there any way to harness some sort of energy, by placing some sort of contraption in it?
You could use a piston and push it using the pressure difference (meh), or you could have something like a windmill to slow down your descent and use the relative air speed to create some power, but it would be just like an "aerial kers", the power you'll recover is negligible.
The biggest problem with generating electricity like this is that maximally you will use the same amount of power raising some mass as you will get from that mass descending. What you need is something which doesn't take electrical energy to raise the mass for you.
And that thing is evaporation.
Hydroelectric dams generate electricity by converting the gravitational potential energy of water into mechanical energy (by turning turbines), and then that mechanical energy into an induced electrical current because magnets ( / Faraday's Law).
This only works because the water is already above the dam; if we had to raise it ourselves then dams wouldn't be worth a damn (only replied so I could make that pun).
I suppose in theory you could generate electricity from anything that's already pretty high up, but other than water you're pretty much limited to kicking rocks down mountains and trying to run them into a mechanical spring (i don't think that trees really go up high enough to use).
Of course, every time you go up the mountain you have to push down ≥ your mass in rocks to come out ahead energy-wise, and that's assuming 100% efficiency in your stupid contraption.