The rated voltage of the 17.5V solar panel is 17.5V. When the 17.5V solar panel charges the corresponding battery, it can only charge the battery when the rated voltage of the battery is lower than the nominal voltage of the 17.5 V solar panel. When the battery is charged normally, the battery's rated voltage is between 15 and 16 volts, so a 17.5V solar panel can charge batteries with a rated voltage between 15 and 16 volts.
I used a 5W solar panel. The output current is theoretically 833mA. The voltage regulator and diode are too big.
First determine what the output voltage of your solar panel is. The output is DC17-18V, resistor 10K, current 100MA, so the power consumption on the resistor is 100W, it would be weird if it doesn't burn! If you want to charge 3.6V battery, it is better to use 7812 plus 7805 to produce 5V to charge the battery.
The easiest way to confirm is that the diode is usually marked, just connect it to the battery in the direction shown. Simply connect the negative terminal to the battery and the positive terminal to the solar panel. The diode is anti-reflux. If the connection method is correct, it will not conduct in the reverse direction and cannot form a loop. Therefore, simply connect a diode to the positive electrode of the solar panel. Otherwise, do not connect it backwards. , there will be no output and it will not work. Acts like a reverse cutoff.