The 2200PRO has an input operating voltage range of 18-100V, and you can freely combine solar panels based on your requirements and the installation area's size. If the solar panel was purchased with the 2200PRO from LANPWR, we recommend the following combinations: 1. Using 4 pcs of 30V/180W solar panels 2 in parallel and 2 in series. 2. Using 4 pcs of 30V/180W solar panels in parallel. If the solar panels are not purchased from LANPWR, we recommend the following combination: 1. Using 4 pcs of 18V/200W solar panels in series. 2. Using 3 pcs of 22V/200W solar panels in series. 3. Using 2 pcs of 36V/550W solar panels in series. Note: No matter how many solar panels are connected in series, the total open-circuit voltage when connected in series must be less than 96V.