If you plan to line up all the solar panels on the long side then you have two options. Either you take solar panel holder part 1 and part 2 or 2 times part 2. See pictures on annex. If you plan to line up two solar panels (as I have built it up, see picture on annex) on the short side then you need solar panel holder Part 1 and Part 2 2 times. The best is, two screw at first the two solar panel holder inside, then slide the panels into the solar holders and the screw the holders outside. See pictures on annex. If you live on the 49 degree latitude, you can use part 3 for the 49 degree slope.