As the wind energy penetration increases, it is becoming more important for wind farms to contribute to frequency regulation, i.e. active power control on the power grid. However, before such controllers can be widely used in industry, they need to be thoroughly validated. This paper contributes to this task by presenting an experimental setup suitable for validation of wind farm control algorithms in wind tunnel experiments. A model free closed loop active power control is implemented on model wind turbines, and tested in a wind tunnel at University of Oldenburg under different operating conditions. Obtained results show that the proposed controller is sufficient for following power references, which is in accordance to numerical studies available in the literature. It is also verified that the controller can react to different disturbances, including variations in the wind farm power reference, and shut-downs of certain turbines in the wind farm. Furthermore, the possibility of coupling the proposed controller with control algorithms for reduction or fairer distribution of structural toads in the wind farm is also demonstrated.