Energy efficiency on computer systems is a topic that is gaining a lot of interest. Even more in the cloud computing era, where data centres consumption corresponds to near 1.5% of total world wide power consumption. In this paper we present two novel approaches for virtual machines (VMs) placement consolidation. The two approaches aim to maximize the placed VMs on a host and therefore minimize the number of hosts used on a cloud computing environment. The first proposed approach is based on the Knapsack problem and the second one is based on an Evolutionary Computation heuristic. Both strategies have shown consumed energy reduction starting from 40.33% and up to 92.21% compared to a strategy that does not consider energy efficiency.