At 0.5 FOM(lowest bound) ~1.1358 maybe 1300m
W=FV
You have 15211W, and gravity gives you 932N resistance for 16.32m/s ideal ascent
FOM(0.8)=9000m/16.32m/s=552s to reach alt
FOM(0.5)=1300m/16.32m/s=80s to reach alt
15211W*552s = 8,396,472J energy required
15211W*80s = 1,216,880J
Assuming...
The Power required might be decreasing, but so is the thrust, as it's also dependent on density, there is a differential in the rates, however.
Too tired to work it out properly, but using Momentum Theory
(hover)
T=2pAVi^2
P=T*Vi=sqrt(T^3/(2pA))
then rearranging
T^3/(2A*P^2)=p
p is...