Energy cells for extrapower. Doesn't make regen faster. EXTREMELY hard to make.
Or some type of engine upgrade where you just go a tiny bit faster or something idk
base: add biodomes, or some sort of solar absorbment for energy, if you're closer/more of a 'victim' to sunlight you can generate some energy for the station
or base types when you are constructing them..
eg battlestations
outposts
depots