If you want to charge the battery, you must ensure that the voltage provided by solar energy is greater than 12V
After meeting the above conditions, the easiest way is to add a Zener diode with a stable voltage of 12V to the circuit. The circuit is as follows: (You can't just download it from the Internet and search for a Zener diode voltage stabilization circuit)
You can also go to the market to buy an adjustable circuit. Built-in voltage stabilized power supply (adjustable range includes the value you need)
Yes This can be done via a 3.0V or 3.3V Zener diode As for the power, it depends of the size of the solar. sign ? How much?
You can use 0.5W 1.0W 2.0W 3.0W 4.0W 5.0W Zener diode