The Solar Cell in our model consists of 4 cells and produces approx 2v with bright sunlight.
The short-circuit current produced is about 30mA and although this is not the correct way to determine the current capability of the cell, it has been given to help you select a suitable cell (or set of cells). The current will drop considerably when the solar cell is connected to a 1.2v battery via a diode and our project delivered 8mA.
The circuit consists of two stages. The first stage is a "switch" or cut-off device. It detects a voltage above 0.7v from the solar panel and the resistance between its collector-emitter terminals reduces to a very small value.
The purpose of the first transistor is to keep the second stage OFF when the solar cell detects sunlight. This allows the energy from the solar cell to be passed to the rechargeable battery. The second transistor is an oscillator. To see how it works we remove the first transistor. The second transistor works by itself. The components in the circuit are: the transistor, the two chokes, the 6k8 resistor, the 1n2 capacitor and the LED.
The main feature of this animation is to show an inductor effectively GROWS when an applied voltage is delivered to it by producing a back-voltage and thus the voltage at its other end does not change until the core is saturated. This understanding is most important in the circuit we are discussing as the top lead of the inductor is taken from a low-voltage to a high voltage by the action of the transistor when it is turning ON and OFF. As the top lead is taken from one voltage-level to the other, the lead connected to the capacitor does not see this rapid change, but continues in the cyclic process of charging and discharging the capacitor. That's why this circuit is so difficult to understand.