actually the "Power" tab under "System" is missing altogether). Another dead end...
I had the same issue - the Microsoft driver that was installed by Windows update for the graphics card is... less than current.
Went to Intel, downloaded the drivers directly, and Microsoft had, of course, blocked them from being installed - had to download the .zip, go to device manager, update manually, then I got the power options - however, for me anyway, the Panel Self Refresh option only shows up in the 'On Battery' section - I switched it anyway, and gave a reboot - I still ran into the issue, but this at least gets me closer.