Ordinary users cannot alter the Power Schemes settings on their PC.

To allow them this privilege, grant them Full Control permissions on the following registry keys and sub-keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Controls Folder\PowerCfg\GlobalPowerPolicy

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Controls Folder\PowerCfg\PowerPolicies

NOTE: You can do this remotely using SetACL.