590
'Windmill': China tests world’s first megawatt-level airship to capture high winds
(interestingengineering.com)
This is a most excellent place for technology news and articles.
I could have stated it better. What I meant was that the fraction of kinetic energy that is taken from the wind is so small that the total kinetic energy in the wind is probably not the important factor that changes with wind speed. The dynamics of how the lift depends on wind speed is probably much more important.
It is actually a notable fraction (~60%) and more importantly constant.
Meaning if your wind has 27x more energy, you can also capture 27x more energy.
This is the energy taken from the wind passing through the disk the turbine spins in, so turbines are placed in spaced out rows to let the wind mix with all the air that didn't pass through a turbine and pick up speed again.