That picture is really poor, but it was handy. I suspect it would be shaped more like one of Colani's three-blade windshield wipers that sweep closely over the zenith. Else...
Flow – Wind Solar Energy System | Tuvie
I now understand these are fixed vanes with a Darius rotor concealed underneath.
Then there's also R B Fuller's rotating ventilator with it's wind powered vacuum cleaner.
