Hi I’d love some feedback on some magical mechanics I was thinking about to add flavour.

It seems like it could be balanced... but the system strikes me as rather unfun to build an RPG narrative around.

A system such as this will run into problems because it requires you track otherwise unimportant details more closely, and punishes or rewards players based on a factor which generally only the GM can control; when an encounter takes place.

Such systems work best in cinema and literature where the author controls the flow of the story, and can use such mechanics to justify a sudden reversal. For example, when a nearly defeated fire-bender is revitalized by the rising sun just in time to turn the tide of a battle.

Narratively, you don't need to assign mechanics to it to have the system add flavor. You can add a lot of narrative flavor to your system simply via framing and nomeculture.

For example, Solar Magic might be 'weaker at night'; but that doesn't mean any given solar mage's spells have to be (especially if they're a PC). Heroes are often the exception to the rule anyway. When they fail during the day, it can be 'because of the sun being blocked at an inopportune moment', meanwhile when they succeed at night it can be 'in spite of using the weak light of distant stars'. Neither of these checks need to have modifiers assigned to them in order to frame their results in a flavorful way. Similarly, magic implements for Solar Magic would work the same as any other; but they'd typically be giant lenses, light-sources, or else common implements decorated with thematically appropriate sun & star motifs.

I like your point in just using it narratives to save on adding rules

You can also introduce a wonderous event (such as a comet passing or proximity to a natural mana-source) when you need to justify an encounter in which a particular kind of spellcaster gains bonuses or suffers penalties. Usually it is simpler and fairer if only NPCs can take advantage of it though, unless all of the PCs benefit.