We have a community for that: !music@slrpnk.net but I don't think there really is a specific music genre for Solarpunk.

Seconding !music@slrpnk.net but in general I'd associate folk and punk rock because of their protest roots.

Folk? Neofolk? Omnia? Faun?

Thinking Omnia's I Don't Speak Human.

Mad Routine is incredibly climate conscious. They regularly upcycle thrifted finds and handmake the majority of their merch. They're also 100% indie, so they avoid these rich corpo labels that prop up industries that are ruining everything. Their fans also care deeply about climate responsibility and hold anti-corporate beliefs, so it's a fun group of people!

I think what's now known as Utopian Scholastic has a particularly solarpunk-y vibe, IMO. You can hear an example here.

GLOBAL PATTERN released several exploratory compilations around solarpunk: https://globalpattern.bandcamp.com/album/solarpunk-a-possible-future

For me it's Bob Marley, of course.

for some reason marimbas or similar?

Interesting question. In a solarpunk world I can imagine every type of music but if I have to find a genre with the vibe I'm thinking about indietronica.

For festivals, Electric Forest and Tomorrowland feel the most solarpunk to me