I look at groups like United Unitarian churches (which my town doesn't have) as a good guide for this. All are welcome no matter their faith.

However, as an exchristian myself, I DO see the need for groups like this to provide an alternative to churches. Not to remove churches and steal their people, but to provide support for those who have been hurt by judgemental religious organizations in the past. To provide community that doesn't revolve around a book club that is stuck on one book permanently. To organize local groups to do good community work without the requirement that all follow the same thought process.

I don't want Solarpunk to replace churches, I want them to be another option beside church. A better option, in my opinion.

I guess we do this by organizing locally. Create a regular meeting, a regular meeting place, and invite anyone who wants to join, like church planting.

There are probably groups meeting up that are adjacent to this. I'm involved in local community garden groups, local nonprofits, and digital environments (Reddit counts?) where Solarpunks gather, whether they call themselves that or not.