Partially, the future of mobile and cellular networks will be about energy consumption savings, at the network infrastructure side. In the heterogeneous cellular networks environment, these can be achieved based on bandwidth adaptation, discontinuous transmission, relays, or even Base Stations (BSs) shutdown when possible. This paper proposes an approach for power savings using Vertical Handovers (VHOs) among different Radio Access Technologies (RATs), based on Radio Resource Management. The presented solution use a utility function focused on the energy efficiency of a given BS and RAT. An active VHO trigger mechanism is also proposed to provide RF power savings by handover mobile terminals to the most efficient RAT. Based on a power model proposed by the ICT-EARTH project, it is possible to translate RF power savings into system level ones. Results show that VHOs RF power gains range up to 46%, and up to 13% at the BS system level.