I mean, let’s be honest: People do crimes even when they have no material need to do so, so you will always need some form of law enforcement, how should a solarpunk society handle this?
The same is true for a military: As long as there is no world peace or some magical way to shut the outside world out, and as long as other societies exist somewhere nearby (and in today’s world this means somewhere on the same planet), a society needs the means to defend itself… what would this look like?
I think there’s a difference between law enforcement and police, though the word “enforcement” does stick in my craw a little. I don’t know if it’s what the OP was getting at, but there does need to be some way to ensure that people don’t abuse others even in an anarchist society.
That could be community intervention in the moment and social services in the long term, with cessation of community support as a last resort for people who simply will not cooperate with the community.
Of course, there would be a lot less crime in a supportive society, but it wouldn’t disappear entirely.
The law part sucks too.
The law is impartial, which is to say it does not care for the wishes of the victim. The law is blind, meaning anyone who finds a loophole is in the clear. The law asks whether people are guilty or innocent, meaning complex situations have to be assigned a binary label.
You’ll want some way to protect people who are in danger from others, whether that’s warning them of others’ selfishness or violent mutual aid. But you don’t need a rigid law for that. Situations can get messy and benefit from things being cleared up, but that’s closer to investigative journalism than to courtrooms referencing obscure clauses written by lawmakers who never conceived of this situation.
Laws were made by centralized states to enforce the wishes of the central authority on its behalf. They are shaped like authority, not justice.