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 lot of colonial American power structures fit the intent of what you’re describing. For law enforcement, the local government would usually designate someone to be the head of law enforcement for day to day activities and there would be a communal drawing of manpower from the local community if the need arose. For the military, you had local militias which had elected officers and would vote on strategic actions if time permitted.
You’re likely going to see a lot of people here completely reject these forms of local communal government because communal doesn’t mean equal. For instance, the enforcement of slavery was a communal action in the South; free whites gladly assisted in the capture of escaped slaves.