This is how we roll with SQL consolidation...

Mark Pohto, one of our Microsoft IT senior system engineer's, just published an excellent technical white paper SQL Server Consolidation at Microsoft on Technet. This paper describes how Microsoft approached the issue of consolidating thousands of SQL Server instances. It's good guidance for how you can save money by consolidating your SQL Server infrastructure. 

Here's the link: https://technet.microsoft.com/en-us/library/dd557540.aspx