As your colony grows and you claim more territory and build more bases, this growth will put a strain on your economy. This strain shows up as inefficiency, which can cause you to lose some of your energy production each turn.
The farther a base is away from your Headquarters base, the more inefficiency it will experience.
Inefficiency can be mitigated at all of your bases by making social engineering choices which increase your EFFICIENCY value. Democratic politices and Green economics each increase efficiency.
Inefficiency can be mitigated at a particular base by building a Children's Creche there.