Vertical axis wind turbine spinner

Intended for 200x200mm printbeds
Wether one takes
a brushless motor or induction motor, and a rectifier,
or
a brushed DC motor
as a generator
This print, a motor + mount, M5 threaded rod and a motor-rod coupling, should get you started with generating electricity.
If one wants to store this energy into batteries, one can take a look at "solar charge controllers"