The maximum input wattage of S2000 Pro is 650W MPPT(18V-70V) . Please choose a solar panel in this voltage range.you could chooe ALLPOWERS 400W solarpanel, multiple 200W solar panels or multiple 100W solar panels in series or in parallel.Please remember that use the solar panels within the range(18V-70V).If you have any questions, please feel free to contact us.