[jacquesm]

The big problem is resonances. A VAWT has various modes of resonance that are very hard to engineer against due to some of their basic properties. The largest of these, the one at Cap Chat in Quebec ended up being scrapped after an embarrassingly short period of operation.

There are some VAWTs in the rockies that lived for more than a decade but they made really little power compared to the amount of money that went into them.

But they look nice and are deceptively simple on paper (one less parameter to deal with due to the fact that you don't need to steer them, and the generator stays at ground level). So likely people will keep trying but it almost certainly isn't going to move the needle in the longer term.

[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.