How did you find HGEs in an uninhabited system?
There's some Systems that the Galaxy Map thinks are Federation (edited)
and have an Economy - all while having 0 Population and additionally having no assets whatsoever.
The Signal Source Generation mechanic, however, is producing a reliable and quite high amount of HGEs in such Systems.
(use EDDB to filter for Federation -> Population 0 Systems)
Hence, they're a good TipOff for more quickly filling up on Core Dynamics Components for example.
Be aware, though, that there's some "depletion" of such Systems, so they can't be used nonstop. After clearing out HGEs in such a System, I found it's best to re-visit them the next day if required.
PS.
Such Systems are not to be confused with Detainment Centers, which will have a perfectly normal Signal Source distribution.