We recommend using a 100W or larger solar panel and a minimum 40Ah battery like the Dometic PLB40. You need a battery with the panel to store the energy coming from the solar panel and then adjust it to the correct voltage for the CFX3.
To determine how long the battery will power a CFX3 for, review the CFX3’s average energy consumption per hour (Ah/h). This is the amount of energy the cooler will use in 1hr for the given internal and ambient temperature. Divide your battery’s usable capacity (Ah) by the CFX3’s average energy consumption (Ah/h) to get the number of hours of run time.
To determine the solar panel’s power input back into the battery, review the solar panel manufacturer’s Amp Output specification to calculate how much input back into the battery you will generate for a given length of time. This is usually between 4-8A max per hour depending on the panel. Plan on roughly 6 hours of sun per day to do your calculation.