Our electric coop billing is set up to take advantage of user solar production.  

You have a solar array that produces 10 kw between 3 and 6 pm and you use 5 kw, the coop now has 5 kw more electric production to charge some else for at a rate of $10 per kw.  The coop peak demand will likely occur when the sun is shinning and your panels are producing electricity.  The coops peak demand on the hot sunny day is what their peak demand charge will be based on(what they pay).  During one day in July it is cloudy between 5 and 6 pm, you do not shut off your AC and use 5 kw and now have a demand charge of $50 for that month and also have set your monthly minimum demand charge for the next 10 months.  Cloud cover cooled off everyone's black roofs enough that coop did not experience peak demand.   

I believe we are a very long ways from our coop having too much of our electricity coming from solar on coop lines.  Our coop has actually built some of their own solar to help reduce their peak demand.