A method of customizing a wind turbine for a site-specific condition, comprising: establishing a design environmental condition for a wind turbine blade with a first annual energy production of the wind turbine when operating under the design environmental condition; determining a site-specific condition that changes a wind loading condition on the blade compared to the design environmental condition; determining a second annual energy production for the wind turbine using the blade under the site specific condition; and providing an add-on device for the blade that establishes an increased annual energy production of the wind turbine under the site-specific condition; wherein the blade comprises a coefficient of lift and a corresponding optimum blade tip speed ratio that establishes a first annual energy production of the wind turbine when operating under the design environmental condition, wherein a site-specific control parameter responsive to the site-specific condition is provided, wherein a control device monitors environmental conditions and controls the add-on device responsive to the site-specific control parameter to optimize annual energy production, and wherein the control device comprises a control logic that varies the coefficient of lift of the blade according to the site specific condition by controlling the add-on device, characterized in that the add-on device comprises a plurality of vortex generators mounted on a track that provides movable positioning of the plurality of vortex generators mounted on a suction side of the blade, the plurality of vortex generators being moved forward to increase the coefficient of lift and backward to reduce the coefficient of lift responsive to the site-specific condition, and wherein the site-specific condition reduces a maximum aerodynamic load or a fatigue load in comparison to the design environmental condition, leaving a load margin for the blade, and the add-on device increases the lift coefficient of the blade, increasing the blade load within the blade load margin under the site-specific condition, reducing the corresponding TSR of the blade and establishing the increased annual energy production. establishing a design environmental condition for a wind turbine blade with a first annual energy production of the wind turbine when operating under the design environmental condition; determining a site-specific condition that changes a wind loading condition on the blade compared to the design environmental condition; determining a second annual energy production for the wind turbine using the blade under the site specific condition; and providing an add-on device for the blade that establishes an increased annual energy production of the wind turbine under the site-specific condition; wherein the blade comprises a coefficient of lift and a corresponding optimum blade tip speed ratio that establishes a first annual energy production of the wind turbine when operating under the design environmental condition, wherein a site-specific control parameter responsive to the site-specific condition is provided, wherein a control device monitors environmental conditions and controls the add-on device responsive to the site-specific control parameter to optimize annual energy production, and wherein the control device comprises a control logic that varies the coefficient of lift of the blade according to the site specific condition by controlling the add-on device, characterized in that the add-on device comprises a plurality of vortex generators mounted on a track that provides movable positioning of the plurality of vortex generators mounted on a suction side of the blade, the plurality of vortex generators being moved forward to increase the coefficient of lift and backward to reduce the coefficient of lift responsive to the site-specific condition, and wherein the site-specific condition reduces a maximum aerodynamic load or a fatigue load in comparison to the design environmental condition, leaving a load margin for the blade, and the add-on device increases the lift coefficient of the blade, increasing the blade load within the blade load margin under the site-specific condition, reducing the corresponding TSR of the blade and establishing the increased annual energy production.