Jed Rothwell wrote:
Robin van Spaandonk wrote:
They have to be tethered, or they won't harvest energy. Free flying craft don't stand still in the wind without expending energy, not what you want.
I figured. I suppose that when a hawk hovers, it is in an updraft or thermal.
Still, I do not understand how to calculate the strength of the tether. It seems to me it must be enough to overcome drag only. The Skypower people are talking about building 20 MW units. Obviously a tether could not withstand the force of wind that creates that much energy! The physics are unclear to me, but the wind energy that goes to spin the turbines does not pull on the tether.
Yes it does, but you need to disentangle the notions of "energy" and "force".
See other posts.
Simple mechanics can be used to put a lower bound on cable tension at a given wind speed and power generation rate in the absence of any drag at all. A precise value for the needed cable tension requires substantial knowledge of aerodynamics and rotor and kite design.
So what does?
- Jed
