This paper applied balanced truncation based model order reduction of wind farms. Starting from a simplified and linearized model of a variable speed wind turbine generator, operating under maximum power tracking, the state space representation of a wind farm is considered. With wind velocities as input, and farm power as the output, the Hankel singular values are computed. These indicate the likely order to which the farm may be reduced to. It is found that reduced model matches well with the initial cluster centers of the distribution of inertia of the WTGs present in the original wind farm. The reduced order model retains the dynamic relationship between the variation in wind speed and consequent power output variations accurately over a wide range of frequencies. (C) 2013 Elsevier Ltd. All rights reserved.