A Network on Chip (NoC) provides the interconnection among Processing Elements (PEs) through routers, which permit hop-by-hop communications between PEs. To cope with higher traffic demands, PEs and routers are running at increasingly higher clock frequencies. Thus the chip power consumption grows rapidly and limits NoC scalability. This paper considers a Manhattan-like mesh (grid) NoC topology. We show how to leverage the traffic unbalancing within the topology to fully exploit the classical technique of Dynamic Voltage and Frequency Scaling (DVFS) to minimize the power consumption. We model the optimal NoC power control problem, and we evaluate the maximum achievable power reduction. Furthermore, we propose three different load-balancing routing schemes, simple to implement, that approximate quite accurately the optimal solution. Simulation results show that, in most of the cases, it is enough to consider only two paths among PEs to balance the traffic and to approach the minimum possible power consumption.