The maximum input wattage of S1500 is 300W MPPT(12V-65V). Please choose a solar panel in this voltage range.you could chooe ALLPOWERS 400W solarpanel, 1pcs to 2pcs 200W solar panel or multiple 100W solar panels in series or in parallel.Please remember that use the solar panels within the range(12V-65V).If you have any questions, please feel free to contact us.