In this study, the analysis of energy and exergy of a horizontal axis wind turbine based on blade element momentum (BEM) theory is presented. The computations are validated against wind tunnel data measured in the MEXICO wind turbine experiment. Blade roughness as one of the important environmental parameters is considered in the computations. Results show that the blade element momentum (BEM) theory has good ability to predict the energy and exergy efficiencies. The computation of energy and exergy exhibits that with the increasing the roughness from 0 mm to 0.5 mm, 2324 W of the output power is reduced. Roughness of 0.5 mm at the wind speed of 16 m/s reduced exergy and energy efficiencies 5.75% and 5.83%, respectively. It is also found that the roughness in the first four months of the operation has a more negative effect on the wind turbine performance.