Does Cybertron have a sun or a star possibly capable of producing solar energy nearby? I don't remember anymore... Sorry to bother you :(
Alright anon, I’ve looked into it and the answer is: it depends on the continuity. In some continuities Cybertron has apparently drifted from it’s star and floats about the galaxy, in others (and you can see in many pictures of Cybertron (Beast wars, Bayformers, Animated) ) that the sun is clearly there, it’s just far away.
Provided whichever Cybertron you’re writing for hasn’t drifted (I believe it’s g1 that’s drifted, and I am not sure of the aligned continuities status) then however far from the sun Cybertron is, it would still be capable of harnessing solar energy. I’m basing this off the fact that; a) Cybertron’s sun does not appear as small as our sun does from Pluto, and b) Our sun (which is by no means an exceptionally powerful one) is so bright that Pluto’s daytime is still 600 times brighter than Earth’s nighttime.
So I think there’s a lot of variables you can work with to get the answer you’re looking for :3 Maybe Cybertron has a really bright star, maybe the metal surface contains natural pockets that retain heat and energy so well that it naturally harvests solar energy, it’s up to you!