You can make this Solar Power supply as your work bench power supply for testing prototypes. It delivers variable voltage from 1.5 volt to 12 volts with a current up to 300 milli amperes. It can also be used to charge batteries during day time. By using the Pot, it is easy to set the output volt from 1.5 to 12 Volts.
A 12 volt 5 Watt Solar panel is sufficient for the power supply. It gives around 18 volt DC in good sunlight and around 350 mA current. So without using electricity, you can run low power devices also. In the circuit, diode D1 is connected to the +ve terminal of the Solar panel and the negative terminal of the panel directly goes to the circuit negative. The high value capacitor C1 acts as a buffer, so that the circuit gets a steady voltage. Variable voltage regulator IC LM317 is used to give a variable output voltage. This IC can give output voltage from 1.5 volt to maximum voltage of the input. Its Adjust pin (pin1) is connected to the negative rail through a 4.7K pot so that, by using this pot, it is easy to adjust the output voltage. Capacitor C2 again acts as a buffer to give steady output voltage.
After connecting the Solar panel in good Sunlight, measure the output voltage using a Multi meter. Then calibrate and mark the voltage level near the pot .