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?
A self-ruling community is not a lawless place, you don’t need to be under government control to set up a police. An example where that is the case is Cherán, where until the 2011 uprising cartels had cut down 60,000 acres under the cover of bribed politicians and a corrupt police. In 2017 Cherán may have had the lowest homicide rate in the entire country of Mexico.