Excel Services and PowerPivot for SharePoint

http://blogs.technet.com/b/excel_services__powerpivot_for_sharepoint_support_blog/archive/2013/11/06/excel-services-2010-amp-2013-kerberos-configuration.aspx

Configure Excel Services in SharePoint Server 2013

http://technet.microsoft.com/en-us/library/jj219698.aspx

Configure Excel Services for Kerberos

http://blogs.technet.com/b/excel_services__powerpivot_for_sharepoint_support_blog/archive/2013/11/06/excel-services-2010-amp-2013-kerberos-configuration.aspx

Identity Delegation for Excel Services

http://technet.microsoft.com/en-us/library/gg502605(v=office.14).aspx

Administer Excel Services in SharePoint 2013

http://technet.microsoft.com/en-us/library/ee681487%28v=office.15%29.aspx