Got this on another site.
Has to be enabled first, start by connecting the Keyboard dock and then pressing Windows + R keys to get “run” window and then type “powercfg.cpl” and hit enter...
This will quickly bring up the power options, then click on “Choose what power buttons do”... From there, click on “Change settings that are currently unavailable”... Scroll down, there you can able to see “Hibernate” option which is not ticked.
So tick it and then click "Save Changes"... Hibernation option should then be available...