In order to run PowerShell cmdlets in SharePoint 2010/2013, user should have necessary privileges to SharePoint object model and to SharePoint databases. Even if a user is added as farm admin, he necessarily do not have access to run powershell cmdlets unless user is having SPShellAdmin access.
Adding users to this access level, provides the ability to run farm level powershell cmdlets in SharePoint
Add SPShell administrator
Add-SPShellAdmin -UserName Domain\username -Database databasename
If -Database attribute and database name are not provided, user is provided access on all the databases in the farm.
Remove SPShell Administrator
Remove-SPShellAdmin -UserName Domain\username -Database databasename