Diagram of solar panels connected in parallel
The diagram shows two solar PV panels connected in parallel so the voltage is the same. To calculate the power rating for a solar charge controller we need to calculate the current flowing in the circuits. Current is always Power (Watts) divided by voltage (Volts) so in this example solar power system it's 120 / 12 = 10 Amps. The Steca PR1515 is fine for this purpose as it is a 15Amp solar charge controller.
Connecting solar panels in series