1. Power Rating (Wattage Of Solar Panels; 100W, 300W, etc) The first factor in calculating solar panel output is the power rating. There are mainly 3 different classes of solar panels: Small solar panels: 5oW and 100W panels. Standard solar panels: 200W, 250W, 300W, 350W, 500W panels. There are a lot of in-between power ratings like 265W, for ...