First wind turbine without blades nor gears
vortexbladeless.com
vortexbladeless.com
A conductive grid stretched between buildings or bridge uprights, or even between wind turbine towers (with or without operating turbines), with a streamer at each intersection made of slightly conductive material that sheds electrons to passing wind, builds up a voltage relative to ground that can do work.
A lightweight grid carried aloft on a kite would extract power proportional to the 4th power of altitude, with the restoring electron current running up the (conductive) kitestring.
Such a system was patented in the '80s by Alvin Marks, holder of the patent on polarizing sunglasses, shortly before he died.
There is no upper limit on the practical size of such a grid, and construction is extremely cheap. Attached to existing structures, it would be designed to extract only a small fraction of available power so as not to exceed the design limit of the structures.
On kites, the sky is the limit. A stacked series of grids could extract up to the theoretical maximum of 30% of incident power. A good place to fly such a kite is in an existing nuclear power plant overflight exclusion zone, where they might extract more power than had been (or is still being) generated below. This also provides convenient access to an existing regional power distribution grid.
Thus far people seem to have been making cathodes like in vacuum tubes, using heat or high voltage to drive electrons out of emitters like you see in ion-generator room-air cleaners.
That might be a dead end, from a complexity, cost, and power waste standpoint. On the other hand, maybe maintaining a second grid at high voltage relative to an emitter array could be simple enough, with just one charge pump for the whole system that need not burn much power.
But a purely passive, air-friction driven system ought to be more foolproof.
Probably either would work, so it just comes down to cost and extraction efficiency. A single active grid that can capture a high fraction of the available power (up to theoretical maximum around 30%) might end up better that a whole bunch of stacked, cheap, passive grids.
The materials science needed to make the somewhat-conductive, hydrophobic, passive-grid streamers that readily give up electrons to colliding air molecules seems within reach, but that is not a thing I know enough about.
Come back when you've demonstrated it.