A detailed explanation of solar street lighting design ideas and points

The application of solar street lights has important practical significance, especially in areas where small-scale thermal power generation or seasonal hydropower generation is used, and solar power should be vigorously developed. Solar street lights are popularized with their advanced, stable, intelligent, mature control technology, significant energy-saving features, and simple maintenance methods. With the popularity of solar lighting products, many applications have quality and after-sales service issues. Therefore, it is necessary to analyze the reasons in a timely manner, regulate the market, and make the solar street lamp market develop in a healthy and orderly manner. Solar energy is the most direct, universal, and clean energy source on the planet. As a renewable energy source, it reaches the earth's surface every day with about 250 million barrels of oil.

This article mainly explains the design of solar street lamps. First of all, it introduces the basic structure of solar street lamps, operation principles and data needed for the design of solar street lamps. Secondly, the design ideas and points of solar street lamps are described. Finally, a smart solar street lamp based on single-chip microcomputer is introduced. Detailed design plan.

1, the basic structure of solar street lights

Solar street lights are mainly composed of solar battery components, components, brackets, light sources, manipulators, batteries, and light poles.

2, solar street lighting operating principle

Solar street lamps use the photovoltaic effect principle of solar cells. Day solar cells absorb solar photon energy and generate electricity. They are stored in the battery through the controller. When the night comes, or when the ambient light is low, the battery is powered by the manipulator to the light source. Blocked after the set time.

1, through the use of known solar street lights to find the longitude and latitude of the application. After the solar radiation database on different slopes of China, the solar cell module's skew angle and azimuth angle were determined, and the solar specification peak sunshine time in this area was calculated.

2. The power of the light source selected by the street light (W). The size of the light source power directly affects the stability of the entire system.

3. Hours (H) for solar street lights to work every night. This is the central parameter of the component size of the solar street lighting system. After determining the operating time, it can begin to calculate the daily power consumption of the load and the corresponding charging current of the solar cell module.

4. The number of consecutive rainy days (d) for solar street lighting demand persists. This parameter determines the size of the battery capacity and the solar module power required for the recovery battery capacity in the rainy days.

5. Determine the number of days D between two consecutive rainy days. This is the battery module power required by the resolution system to flood the battery after a series of rainy days.

The basic principle of solar photovoltaic power generation system is the same, so solar street light design ideas can also be based on the general solar power generation system, first determine the power of the light source, daily working hours, to ensure a few rainy days and then calculate the battery capacity and the solar cell module power. However, solar street lamps have their own special characteristics and need to ensure the stability and reliability of the system. Therefore, special attention must be paid to the design of solar street lamps.

1, solar module

The voltage of the solar cell module will decrease as the temperature increases. Due to the effect of high temperature, the voltage loss of the battery module is about 2V, and the voltage drop of the diode on the charging process controller is 0.7V, so the module with an operating voltage of 18V is selected. Due to the special nature of solar street lights, solar panels are generally installed on the light poles. For street light poles, they are generally more than 5 meters with a high center of gravity, and most of the solar panels are suspended to enhance the entire set of equipment. Resistance to wind, generally choose a number of solar panel components required for component power.

2. Battery (Group)

When selecting a battery, it is necessary to consider the influence of the discharge rate on the battery capacity, the influence of temperature on the battery capacity, and the influence of the depth of discharge on the battery capacity. Therefore, we must choose a deep cycle solar battery. When batteries are connected in parallel, it is necessary to consider the unbalanced effects among the individual cells. Under normal circumstances, the number of parallel groups should not exceed 4 groups.

3, controller

The controller is the key component of the entire street lighting system as a manager. Its maximum function is to conduct comprehensive management of the battery. A good controller should set various key parameters, such as the overcharge point of the battery, according to the characteristics of the battery. Over-discharge, recovery of connection points and SOC discharge control. When selecting the street lamp controller, it is necessary to pay special attention to the controller to restore the connection point parameters. Since the battery has the voltage self-recovery characteristics, when the battery is in the over-discharge state, the controller cuts off the load, and then the battery voltage recovers, if the controller parameters Improper setting of the point may cause the lamp to flicker, shortening the life of the battery and the light source.

4, the choice of light source

The selection of light sources is the most critical step for solar street lights. At present, there are fewer light sources for solar street lights. In order to reduce the loss of limited energy, the light source should be selected as possible. Current common light sources include DC energy-saving lamps, high-frequency electrodeless lamps, low-pressure sodium lamps, and LED light sources. As a semiconductor light source, LED has a strong development momentum. It is the most ideal light source for solar street lights. LED street light source is a multi-functional, environmentally-friendly and energy-saving street light source suitable for lighting in various occasions. The LED street light driver is a product specifically developed for the LED street light system and is used to provide a stable power source for the LED lighting. Using advanced electronic power technology, two types of output modes, high-efficiency enhancement and ultra-energy saving pulse width modulation (PWM), have been designed. With time control, the time can be increased when needed (at the end of the day when many blacks are more cars). The efficiency enhancement mode illuminates the LED lamps and provides good lighting, while other time periods (when the rear of the vehicle is scarce) are output in a super energy-saving mode, saving the power consumption of the battery. In addition, most of the solar street lighting projects in China need to meet the city road lighting standards.

The following is an example of the design of solar street lighting system:

For example, it is necessary to install a batch of solar street lights in a certain city. The power of the light source is 30 W. The street lights are required to work for 8 hours every day to ensure that 7 consecutive rainy days can work normally. It is 114 degrees east longitude, 23 degrees north latitude, the annual average solar radiation is 3.82 KW.h/m2, and the average monthly temperature is 20.5 degrees. The interval between two consecutive rainy days is 25 days.

Based on the above data, the tilt angle of the photovoltaic module was calculated to be 26 degrees, and the standard peak hour was about 3.9 hours.

(1) Daily load power consumption

Q=W* H/U=30*8/12=20Ah

Where U is the nominal voltage of the system battery

(2) Charging current of a solar cell module meeting daily load

I1=Q*1.05/h/0.85/0.9=7.04A

In the formula 1.05 is the comprehensive loss coefficient of solar charging, battery charging efficiency, controller efficiency

(3) Determination of battery capacity

Satisfy the normal battery capacity for 10 consecutive rainy days

C=Q*(d+1)/0.75*1.1=20*8/0.75*1.1=235Ah takes 240Ah

In the formula, 0.75 is the battery discharge depth, and 1.1 is the battery safety factor.

Select two 12V120Ah batteries to form a battery pack

(4) Solar cell module charging current I2 that needs to recover battery capacity after continuous rainy days

I2=C*0.75/h/D=240*0.75/3.9/25=1.85A

0.75 for battery discharge depth

(5) The power of the solar cell module is (I1+I2)*18=(1.85+7.04)*18=160Wp

Where 18 is the operating voltage of the solar module

What is a solar street light design scheme based on the intelligent control of a single chip microcomputer? This scheme can not only achieve intelligent control, but also enable the street light system to operate in a state of energy saving and improve the utilization of energy.

1, hardware circuit design

Select DS1302 timer, AT24C02 memory, 4-digit display, over charge and discharge circuit, STC12C2051 microcontroller and other intelligent control system. According to the different functions of each part of the circuit, the overall circuit can be divided into the following parts: solar panel components, overcharge and overdischarge circuit, STC12C2051 microcontroller, battery, time-controlled light control circuit, lighting load and time display circuit.

1) Power Circuit Design

The power circuit is shown in Figure 1. The system is powered by a solar panel, and the 24 V battery voltage generates a 5 V voltage after being regulated by the 7805, which acts as the main power source for the controller. Capacitor C2 acts as a high frequency bypass capacitor, bypassing the high frequency signal to ground. The same capacitor C1 is a filter capacitor.

Figure 1 Power Circuit

2) Plan selection

DS1302 is a high-performance, low-power, real-time clock circuit with RAM introduced by Dallas, USA. It can time year, month, day, day, hour, minute and second, and has a leap year compensation function. For 2.5 ~ 5.5V using the three-wire interface and the CPU for synchronous communication, and can be used to send multiple bursts of clock signals or RAM data. The DS1302 has a 31x8 RAM register for temporary data storage. The DS1302 is an upgrade of the DS1202 and is compatible with the DS1202, but with the addition of the main power/back power dual power pins and the ability to charge the back power with a trickle current.

In the design of commonly used timing function circuit software timing, timer timing, but its disadvantage is that the timing error, need to be corrected once every other time; the other is the hardware timing, the popular serial clock circuit has DS1302, DS1 307, PCF8485, etc. These circuits are widely used because of their simple interfaces, low cost, and ease of use. In the design of hardware timing, clock chip DS1302. DS1302 is a kind of Dallas company's circuit with a trickle current charging capability, the main feature is the use of serial data transmission, can provide a programmable charging function for the power-down protection power supply, and can turn off the charging function.

The RST input has two functions: First, RST turns on the control logic, allowing the address/command sequence to be sent to the shift register. Second, RST provides means to terminate the transmission of single-byte or multibyte data. When RST is high, all data transfers are initiated, allowing the DS1302 to operate. If RST is driven low during the transfer, the data transfer will be terminated and the I/O pin will be in a high-impedance state.

The clock controller-type street lamp controller is used to set the switching time in advance so that the street lamp lights on time and turns off on time, thereby achieving the purpose of automatic control. The advantage is that the preset switching time of the timing switch is free from external interference, and no malfunction is caused except its own fault. The disadvantage is that it can not automatically change the switching time according to the seasonal changes and special weather conditions. It is necessary to manually adjust the switching time, which takes time and effort and is not conducive to energy saving. Time switch is divided into mechanical clock type and electronic clock type, mechanical clock type is mainly based on quartz clock, accurate travel time, but due to the use of plastic gear inside the movement will be deformed at high temperatures, resulting in shutdown phenomenon.

There are also many electronic clock-type time switches, commonly used electronic clock circuits such as LR6818, LM8650, and LM8561. Fig. 2 is the connection diagram with the one-chip computer, among them VCC1 is the main power source, VCC2 is the backup power source. Under normal circumstances, SCL, I / O, RST and microcontroller connected to achieve 1302 read and write control.

Figure two 1302 interface with the microcontroller

The AT2402's pins 1, 2 and 3 are empty, pin 4 is ground, pin 5 is data, pin 6 is clock, pin 7 is write-protected, and pin 8 is power.

The function of the AT24C02 in the design is the power-down memory, which is to prevent the user information from being lost when the power supply is suddenly disconnected, and to store the current setting information. AT24C02 is Atmel's 2 kB electrically erasable memory chip. Since AT24C 02's data line and address line are multiplexed, the serial port is used to transmit data, so only two lines SCL (shift pulse) and SDA are used. (data/address) and microcontroller transmit data. The voltage is as low as 2.5 V, the rated current is 1 mA, and the quiescent current is 10 μA (5.5 V). The on-chip data can be stored for a long time in the event of a power failure. The 8-pin DIP package is used for ease of use. Its connection with the microcontroller shown in Figure 3.

Figure 3 24C02 interface with the microcontroller

The functions of the solar street light and the ordinary street light control circuit are basically the same. They are all for completing the lighting in the evening, turning off the lights in the morning and charging the battery. The commonly used controllers at home and abroad have separate light control, clock control, and latitude and longitude type controllers, but due to their different working principles, each has its own advantages and disadvantages.

2, software design

The system software design mainly includes the program initialization, the time setting subroutine, the 1302 read/write program, the 24C02 read/write program, the time comparison subroutine, the key subroutine, and the display refresh subroutine. The program starts to initialize, call 24C02 internal storage switch lights time point, the program adjusts the time in 1302 at intervals. The time set by the program is compared with the current time of the system, and the set comparison interval is 1 s/time. When the time is the same, the control signal is output through the program, as shown in FIG. 4 .

The device parameters in the energy circuit part can be calculated. The driving circuit is a mature circuit and has been widely used. The algorithm program of the single chip has been successfully run on the development board. The device parameters can also determine that the algorithm program of the SCM is running on the development board to reach the intended purpose. Therefore, the solution is feasible. Figure 5 shows the part of the system simulation circuit diagram, Figure 6 is overshoot over discharge circuit diagram. The theoretical value of this system is 12 V, the actual measurement value is 9.4 V, there is a certain error.

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