I use the Power = Power Coefficient x 0.5 x Swept Area x Air Density x Velocity3 to do the calculation which has the different answer from what I get from HOMER.  If you use the same formular, could you please tell me what value of the Power Coefficient do you take?

HOMER does not use that approach to calculate the wind turbine output because the power coefficient changes with wind speed.  Every wind turbine has a power curve specifying power output versus wind speed.  HOMER just refers to the power curve when calculating wind turbine power output.  Please look up ‘wind turbine power output’ in the index of the help file for details.