A solar cell power system can be built using this electronic scheme. This electronic circuit is composed of three parts: a diode, solar cell panel and a rechargeable battery. Diode prevents battery discharge through the solar panel in the absence of sunlight or low light. Although diode is usually Schottky type, the direct voltage it can produce a considerable energy loss. Circuit uses a specials diode with low direct voltage.
To adjust the circuit, replace solar panel with adjustable stabilized voltage source, with current limiter set at a level which is not dangerous to the battery. Adjust power supply output at a level higher than 0.1 V than battery voltage. Then, adjust P1 until the point where IC1's output went into logical "1". Finally, with an ammeter if the battery is discharged when the source voltage is below the current battery voltage.