To select a solar regulator you need to know the following:

1. The total solar array output voltage
   If two similar 12V solar panels are connected in series then their combined output volts going to the regulator will be doubled but their output current will not double. That requires a solar regulator that can operate on 24V. Some solar regulators can operate on both 12V and 24V.
2. The total solar array output current
   If two similar 12V solar panels are connected in parallel then their combined output amps is doubled but their output voltage remains the same. Solar regulators have a maximum amps rating and the current from the solar panels must  not exceed that rating.

Please note that some of these solar regulators do not have lighting timer controllers.