It's an aesthetic. And yes aesthetics are political, but I think this is one of those ones that can go either way, in fact I feel that way about most "Punk" genres. There's been progressive and reactionary cyberpunk, steampunk, whatever.

Some of solar punk seems to be "hey what if we did Soviet brutalist commie blocks but with more greenery", so a more naturalistic and whimsical version of dense, organized, urban-proletariat society, which I think is kinda cool. Other times it looks more like an idealized version of what "techno-feudalism" would look like, a quaint, pastoral, sustainable version of being petite-bourgeois.