Michael is one of only two angels named in the Hebrew Bible, and everything he does there is national rather than planetary. Daniel calls him one of the chief princes, then your prince, then the great prince who stands over the sons of your people. He is a guardian assigned to a nation, and he appears in the middle of a conflict between such guardians.
The New Testament adds two scenes. Jude has him disputing with the devil over the body of Moses and declining to bring a railing accusation, a passage that quotes a text no longer in the canon. Revelation has him leading the armies of heaven against the dragon. The Qur'an names Mika'il once, alongside Jibril, in a warning to those who set themselves against God's angels.
From those few verses grew one of the largest cults in Christendom, and it settled on high and remote places. The shrine on Monte Sant'Angelo in the Gargano is the oldest in the Latin West; Mont-Saint-Michel in Normandy, St Michael's Mount in Cornwall and the monastic rock of Skellig Michael off Kerry repeat the pattern along the Atlantic. His feast on 29 September became Michaelmas, one of the English quarter days, which is how a warrior angel ended up governing rents and the start of the legal and academic year.
The Latin requiem asks that the standard-bearer Michael bring the souls of the dead into the holy light, so he weighs and escorts as well as fights, and medieval judgement scenes hand him the scales.
None of that is solar. The attribution of Michael to the Sun is a later overlay, laid by the magical literature onto a figure who already had scripture, a cult and several hundred churches.