The cost electricity from wind turbines is still too for most situations and the cost of electricity has fallen very slowly over the last 30 years (about 2% a year). Even worse, the costs have risen over the last two years. These slides show that the falling costs of electricity from wind turbines are primarily from increases in the scale of wind turbines and that the recent increases are probably from increasing the scale of the rotor diameter too much. Increases in the rotor diameter and the height of towers have directly and indirectly led to reductions in the cost of electricity from wind turbines. They have directly led to reductions in cost because the output of a wind turbine is a function of diameter squared and they indirectly led to reductions in cost because output is a function of wind speed cubed and larger wind turbines can handle higher wind speeds. The major challenge for further increasing the scale of wind turbines is finding materials for the turbine blades that have higher strength to weight ratios. Finally, several new wind turbine designs may also lead to lower costs of electricity from wind turbines.