The solar panels that are sold as 12V don’t actually putout 12V. The output voltage varies between 16V to 20V depending on temperature, weather and location. This is because these panels are implemented to charge 12V battery where the charging voltage is around 14V and the voltage that is supplied by the panel has to be higher than 14V so it can force the amps in.
If we simply connect solar panel directly to battery, the battery will be cooked because the output voltage is way higher than the charging voltage. Regulators are there to regulate the voltage down to the suitable charging voltage. Some advanced model may let you to choose your battery type as the nominal charging voltage can be slightly different.
What size regulator should I use?
A solar regulator must be able to handle the maximum current that can be produced by the solar panels.
Reflected sunlight and specific temperature conditions can increase the output current of a solar panel by as much as 25% above it’s rated output current. The solar regulator must be sized to handle the increased current.
Solar regulators often short the solar panel input when regulating. This does not damage the solar panel, but it does mean that the solar regulator must be sized to handle 125% of the solar panel’s rated short circuit current.
A InstaPower 100W solar panel has a rated output current of 5.56 Amps and a rated short circuit current of 5.95 Amps.
Minimum solar regulator size for a single InstaPower 100W solar panel would be: 5.95 Amps x 1.25 = 7.4 Amps.
It is recommended that the regulator selected is even slightly larger than this figure to ensure that it is not constantly operating at 100% of its rating, particularly in regions with higher ambient temperatures.