The answer to this question relies on the type of appliances you wish to power using solar panels. Remember that all electric devices right from your portable chargers to refrigerators are measured in Amps. It denotes the fastness of the flow of the electric current into the device. It means that bigger power denotes more electricity. Calculate how much electrical load you will require. You should know the total amps that those devices will draw from the solar panels. You can get to know the amp capacity of each device right from the device body itself. Knowing the amperage will aid you with identifying just how big an auxiliary battery you will require. Further, decide on the size based on how long you will power the devices using the power generated by the panels. This is called amp hours or Ah. It is the total number of amps generated from the number of hours you should draw the electricity.