There are literally thousands of grows in rural Northern California. You have to either be in an area where they're specifically cracking down, or have a neighbor complain, or be tweeker trash where the cops are coming out every week, before they care enough to shut it down. They only "know" in the sense that they fly over sometimes and say "I guess that guy has weed", otherwise they know as much as anyone on google satellite view. A couple hoops and some full sun isn't really cause for concern, they're mostly looking for cartel grows with thousands of plants.