The rising energy costs for keeping up large-scale server clusters is becoming an increasingly important concern for many businesses. In this paper, we present a dynamic configuration model for consolidating multiple services or applications in virtualized server clusters aimed at optimizing power consumption. Dynamic configurations in the cluster include turning servers off in periods of low activity and turning them back on when the demand increases. In our model, we incorporate the often ignored switching penalty in order to avoid frequent and undesirable turning servers on/off. In addition, our model takes advantage of the dynamic voltage/frequency scaling capability of current processor architectures to further optimize power consumption. We present simulation results that to evaluate the quality of the solutions and the scalability of the proposed model.