Anything early game to throw energy credits at? I haven't met any other species yet, so can't trade it. I am a bit low on minerals, so that's my limit on clearing tile blockers. Likewise for building anything to raise the maintenance. However, even at just +8 energy I am quickly approaching cap.
Energy is mainly used for ongoing maintenance of buildings, ships, armies, stations etc.
It's main "spending" uses are: removing tile blockers (very useful) and building robotic pops (very useful)
Keep that in mind, you wanna have an energy surplus while colonizing planets.