Thirty-five kilowatt hours of electricity per day requires the design of 50.4 square feet of solar panels. According to the relevant public information request, assuming that 35 kilowatt hours of electricity are required per day, if the solar panel voltage is 12 V, then the current required per day is 2.92 A (35÷12) , and assuming that the conversion efficiency of the solar panel is 20%, then the required area of the solar panel is (2.92÷0.2)×24=350.4 square feet.
How to design a 400W, 72V solar panel, folks.
Working principle
Due to significant changes in sunlight and the relatively high internal resistance of solar cells during use, the output voltage is unstable and the output current is also low. This requires a DC conversion circuit to convert the voltage needed to charge the cell phone battery. ThisDC conversion circuit is shown in Figure 1. It is a single-tube DC conversion circuit in the form of a single-ended flyback converter circuit. When the switch VT1 is turned on, the induced voltage of the primary coil NP of the high frequency transformer T1 is 1 positive and 2 negative, the secondary coil Ns is 5 positive and 6 negative, and the rectifier diode VD1 is cut off -off state. At this time, the high frequency transformer T1 passes through the primary coil Np and stores energy when the switching tube VT1 is turned off, the secondary coil Ns is 5 negative and 6 positive, and the energy stored in the high. -the frequency transformer T1 is rectified by VD1 and filtered by the capacitor C3 before being sent to the load.
The working principle of the circuit is briefly described as follows:
Transistor VT1 is a switching power tube. It forms a self-excited oscillation circuit with T1, R1, R3. , C2, etc. After adding the input power, current flows to the base of VT1 through the start resistor R1, causing VT1 to conduct.
After VT1 is turned on, the input DC voltage is applied to the primary coil Np of the transformer, and its collector current Ic increases linearly in Np. The feedback coil Nb generates an induced voltage of 3 positive and. 4 negative, which causes VT1 to obtain the base voltage. The positive feedback voltage is extremely positive and the emitter is extremely negative. This voltage injects a base current into VT1 via C2 and R3 to further increase the collector current of VT1. avalanche process, causing saturation and conduction of VT1. During the saturated conduction period of VT1, T1 stores magnetic energy through the primary coil Np.
At the same time, the induced voltage charges C2. As the charging voltage of C2 increases, the base potential of VT1 gradually decreases when the change of the base current of VT1 cannot satisfy its continuous saturation. VT1? exits The saturation zone enters the amplification zone.
After VT1 enters the amplification state, its collector current decreases from the maximum value before the amplification state, and an induced voltage of 3 negative and 4 positive is generated in the feedback coil Nb, which reduces the base current. of the VT1 and its collector. The current decreases accordingly, positive feedback occurs again through an avalanche process and VT1 is quickly cut off.
After VT1 is cut off, the energy stored in transformer T1 is supplied to the load. The 5 negative and 6 positive voltages generated by the secondary coil Ns are rectified and filtered by the diode VD1, then one. A DC voltage is obtained on C3 to charge the cell phone battery.
LWhen VT1 is cut off, the DC power supply is input. The 3 negative and 4 positive voltages induced by the voltage and Nb reversely charge C2 through R1 and R3, gradually increasing the base potential of VT1, making it cycle back, turn around and reach the saturation, and the circuit will oscillate repeatedly.
R5, R6, VD2, VT2, etc. form a voltage limiting circuit to protect the battery against overcharging. Here, taking a 3.6V mobile phone battery as an example, the charging limit voltage is 4.2V. During the battery charging process, the battery voltage gradually increases. When the charging voltage is higher than 4.2V, the voltage regulator diode VD2 starts to conduct after being divided by R5 and R6, causing VT2 to conduct. reduces the base voltage of the pole current of VT1, thereby reducing the collector current Ic of VT1, thereby limiting the output voltage. At this moment, theThe circuit stops charging the battery with high current and uses low current to maintain the battery voltage at 4.2 V.
Component selection, installation and debugging
VT1 requires Icm>0.5A, hEF is 50-100, 2SC2500, 2SC1008, etc. can be used, VD1 is a Zener diode with a stable voltage value of 3 V.
The high frequency transformer T1 must be homemade, using an E16 ferrite core. Np is wound with 26 turns of φ0.21 enameled wire, Nb is wound with 8 turns of φ0.21 enameled wire and. Ns is wound with φ0.41 enameled wire over 15 turns. When winding, pay attention to the starting ends of each coil so as not to cause the circuit to vibrate or the output voltage to be abnormal. During assembly, a layer of plastic film with a thickness of about 0.03mm is placed between the two magnetic cores to serve as the core air gap.
The solar panel uses four solar panelssilicon ires with an area of 6 cm × 6 cm. Its no-load output voltage is 4V, and when the operating current is 40mA, the output voltage is 3V. Since the working efficiency of the DC converter increases with increasing voltage input, four solar panels are used in series. At this point, the input voltage of the circuit is 12V. Readers can decide how many and connection methods to use based on the specifications of the solar panels you can buy.
See Figure 1 for parameters of other components.
The printed circuit is shown in Figure 2, the size is 45×26 mm2.
After installation is complete, connect the solar panel and place it in the sun. At no load, the output voltage of the circuit is about 4.2V. When the no-load output voltage is greater than 4.2V, it can be appropriately reduced the resistance of R5, otherwise atincrease the resistance of R5. The operating current of the circuit is related to the intensity of sunlight. Normally it is around 40 mA. The charging current is approximately 85 mA.
The average maximum power of this solar panel is 280 W and the corresponding maximum voltage is 31.5 volts. Theoretically, let's take this card as an example:
3 cards in series: 31.5×3=94.5V
Maximum output power: 280×3=840W
Here, the result is only an instantaneous state rather than a stable state.
It is only an ideal state, and there is a large distance between the ideal and reality.
Parallel or mixedThe joint calculation is also based on the performance of solar panels
For reference only