How to make a small solar panel

The basic principle of solar power is: the collected light energy is converted into electrical energy and stored, and the stored electrical energy is released when the load is turned on. A typical example of solar power is solar street lights: when there is sunlight during the day, the battery is charged, and at night, the battery is used to supply power to the light bulb (mostly low-power high-brightness LED) for lighting. Many urban trunk road lights have begun to use this solar power source. An actual solar power source is relatively complex, but no matter how complex it is, its principle is the same. Of course, there is no need to make a miniature solar power source so complicated.

The principle and design of solar power panels

After understanding the actual solar power source, the author began to design a solar power panel. My overall idea is: charge and store energy for 1.2V rechargeable batteries through solar panels, and then use the boost circuit to boost 1.2V to more than 3V for load use. Some people may say: Why not just use several rechargeable batteries in series to store energy and output, so that the boost circuit can be omitted? Why do we have to take such a detour in the middle? Because we are going to use solar panels to charge batteries. After all, solar panels have few opportunities to generate higher voltages . If the battery's own voltage is too high, charging will not be possible. For this kind of solar panel I have, the output voltage can reach more than 1.2 volts in a place with good light near the window indoors (when connected to the circuit, not in an unloaded state), so it starts to charge a battery with a rated voltage of 1.2V, but if it is to output a voltage of more than 3V, it may have to be taken out of the sun. The advantage of using a battery to store energy is that it can greatly reduce the light intensity requirements for charging and extend the time to charge the battery.

The circuit of the solar panel is shown in Figure 1. The solar charging circuit of the system is composed of D1 and BT. Usually, as long as a certain light intensity is reached, the solar panel will charge the rechargeable battery BT through the diode D1 until it is saturated. In addition to the solar charging method, I also designed a backup external DC power charging interface in case of emergency. The external charging circuit is composed of R1, DS1, D2, and BT. R1 uses a 1W resistor . When R1 is 10 ohms, the optimal external charging voltage is 3-4 volts. DS1 is an external charging indicator light, which is lit by the voltage drop on the resistor R1. The following boost circuit uses the fast shutdown (cutoff) characteristics of the intermittent oscillator to achieve boost. S1 is the power switch. When S1 is closed, the boost circuit starts to work, and the solar panel can drive the load. J1 is the output interface and DS2 is the output indicator light.

Component Selection

The price of commercially available solar panels is generally high, but we don't need to buy a large solar panel, a moderate one will do. According to actual measurements, the open circuit voltage of a single solar panel used by the author in this production can reach 4.2V, and the short circuit current can reach 38mA. The entire system is built on a universal circuit board (commonly known as a "perforated board"), so a universal circuit board is required. Figure 2 shows the two prepared solar panels and the perforated board. The battery can be a regular No. 5 nickel-hydrogen rechargeable battery with a rated voltage of 1.2V. The boost circuit can use the ready-made boost circuit board in a single-battery high-brightness LED flashlight. The author dismantled the boost circuit board in a discarded single-battery high-brightness LED flashlight. If you need to make it yourself, use Φ0.4mm enameled wire to wind 15 and 9 turns of inductor T1 on a Φ8mm small magnetic ring. The small magnetic ring can be removed from a discarded energy-saving lamp. If you can't find the diode IN5819, you can use IN4148 instead. C1 uses a 100uF tantalum capacitor . If you don't have it, you can use an electrolytic capacitor of the same value instead, but the efficiency is slightly lower.

Production process

First, cut a small piece of metal wire and weld it to the two electrodes of the solar panel as pins (Figure 3) to facilitate connection and fixing on the circuit board. The two solar panels are connected in parallel with positive poles facing positive poles and negative poles facing negative poles (with markings on them) , which can effectively enhance the ability of the solar panel to provide current . After the solar panel is installed, it is shown in Figure 4.

When installing a rechargeable battery for energy storage, you can also connect the positive and negative terminals of the battery to the circuit board as shown in Figure 3 , that is, solder pins on both poles of the battery to the circuit board. For stability, you can use a pointed metal tool to drill holes in the circuit board and then use nylon strapping to reinforce it (Figure 5).

Next, connect the small boost circuit board removed from the waste single-cell high-brightness LED flashlight to the circuit board. The positive pole of the two wires connected to the battery in the removed boost circuit board is connected to point a in Figure 1, and the negative pole is connected to point b; the positive pole of the two wires connected to the LED light is connected to point c, and the negative pole is connected to point d. When I made it, the boost circuit board was connected to the main circuit board below through the DuPont pin header (Figure 6). You can use your own method as long as it is easy to make. If you make the boost circuit yourself, you can directly route it on the perforated board. The selection of components has been explained in detail above and will not be repeated. The circuit is not complicated, you can play freely on the perforated board.

Figure 7 shows the finished solar panel, which can be used to power small items such as flashlights, radios, etc. Connecting a few high-brightness white LEDs will make it a solar LED flashlight. Figure 8 shows the solar panel lighting up the high-brightness LEDs.

Since the volume issue was not taken into consideration during production and there was a lack of experience in this area, the circuit board was a bit large and there was no casing, making it very inconvenient to carry. Therefore, it is hoped that enthusiasts will use their imagination when making it and design the appearance to be exquisite and compact, so that it will be more beautiful and easier to carry, thereby increasing its practicality.