Wind power. Modern wind generators or Vertical Axis Wind Turbines (VAWT). Two catenary-shaped aluminium blades are fixed along a rotating column giving the structures their distinctive 'eggbeater' appearance. Despite the fact that these turbines are not self-starting even in high winds, they do have a number of advantages over the conventional horizontal axis aerogenerators; the axial symmetry of their design obviates the need for re-alignment in response to shifting wind direction and there is no need for the generator itself to be mounted at the top of the tower. Photographed at Altamont Pass, California, USA.