It's complicated for a number of reasons. One issue is that the vanilla heat exchanger is tuned for use with nuclear, not solar thermal. And the Nullius heat exchanger only makes sense for Nullius's different fluids. For vanilla water I'd need to implement a new lower temperature version and make it visually distinct from vanilla, perhaps just by tinting it.
Vanilla heat pipe is a little too high tech because it's meant for nuclear, but I guess we could just have it be unlocked with solar thermal tech too without much trouble. It also doesn't really make sense to have multiple tiers of solar collector in vanilla like it does in Nullius. But someone using it in another mod pack might want tiers. There's a significant amount of adaptation that would be required for it to be standalone.
Also the collector graphics are kind of placeholder graphics that could use proper 3d artwork, and having it be a standalone mod would really put those front and center. It seems a bit unfinished to promote it as it's own feature without more polished art.
