Just added another 8 panels to the system but will need to add 1 more so as to not have to use another charge controller..existing panels were 235watts each and the new one’s are 300 watts each.Will need to add another panel to match incoming voltage with the other 8..The first 8 are made up of 2 sets of 4 panels in series then paralleled. The new set will be 3 sets of 3 panels in series and then paralleled. This has to be done to almost match the incoming voltage to the charge controller.. Otherwise you would need 2 controllers, One for each set of panels and voltages, to keep maximum input from all panels. We will still be adding another 9 or 18 panels before the system is at capacity. This system is one of those that I have spoken about before. When possible we should build a system that will meet the needs for the home owner..If not affordable or warranted at time of start, then start and build as you go. just try to build with the products you want in your completed system. Try not to have to buy products twice to finish the system..Most systems can be built is such a way as to grow as you go, just start out with the right products. This set of panels will also get 1/2 inch hardware cloth added to keep down possible hail damage.