[hinkley]

If memory serves, the resonance problem with 3 blade turbines is when the blade passes in front of the pylon. But with the VAWT the blades instead pass into the shadow of every other blade, which is twice per revolution?

Does a VAWT behave better or worse in this regard with an even number of blades? Seems like with an even number multiple blades would occlude each other at the exact same time.

[jacquesm]

It is the tower occlusion that sets off the problematic resonance, which ends up eating the base bearings.

[bigiain]

There are a couple of (small, obviously academic/experimental) vertical axis wind turbines near me which both have helical blades. I wonder what the tradeoffs for that design are?

Here's a picture (not mine) one of them: https://www.flickr.com/photos/nicephotog/25044930672/

[hasmanean]

For very tall VAWTs in a grid, could you dampen the resonances by tying the tops of the masts together with guy wires?

[jacquesm]

That will make it worse, not better. You want to decouple as much as you can so you don't end up creating a giant resonant structure.

[jacquesm]

They're sexy toys, not turbines.

See also: Windtree and other scams.