The solar panel selection is decided by the following two factors:

1) The quantities of electricity spent over your system, at the average shining sunlight during one day, you have to consider that the solar panel can fully charge your battery to compensate the electricity consumption, if the power of solar panel is insufficient, it will make the battery at under-charge statue on certain time, If the battery can not get fully charge for long term, the battery is easier to be sulphated and shorten life even damaged; If the battery is always fully charged, it will prolong the battery life, that is to say, there is a relationship of direct proportion between the battery life and its fully charge acceptance.

2) The specification of solar panel, except the difference of wafer type with monocrystalline silicon, polysrystalline silicon or amorphous in a solar panel, for a PWM type solar controller, firstly, you must select the proper output voltage of solar panel,

For example: in a 12V battery system, you have to select 36 cell solar panel with 17~18V output voltage; in a 24V battery system, you have to select 72 cell solar panel with 34~36V output voltage, there are many 60 cell solar panels for other on-grid application in the market, it is not suitable for using the PWM solar charge controller.