well we went through the entire winter with only one string of panels working. not actually quite sure how much we'd have available. we can only guess based on the fact that right after we fixed it (at the tail end of this winter), we immediately had more than enough! we designed it to grow into it without having to replace major parts. so far so good! (and all that was wrong this winter was a broken mc4 connector on the roof- gah!! haha)