Design of solar street lighting system for coal entering the market

1 Overview
As a new renewable energy source, solar energy has gradually entered various industries. In particular, solar power generation systems are in a booming stage. Many coal research institutes and factories are currently studying how to apply solar cell systems to traditional coal enterprises. Technology, cost and many other issues, the application of solar street lamps in China is still in a sluggish state.

In the long run, the future of solar lighting systems is broad. Solar lighting will become popular in the next decade and become the development trend of the lighting industry in the future. In cities with energy shortages, power cuts, industrial and mining enterprises, and remote areas where electricity is difficult, they have strong promotion.

The article will introduce the solar cell-driven new LED street light system applied to the traditional coal approach street lighting system to achieve the perfect combination of new energy and traditional energy.

The street lighting system uses SPCE061A single-chip microcomputer as the control core to control the battery charging and discharging of the solar street lamp system, and drive the LED street lamp to meet the night lighting requirements.

2 system design
The solar street lighting system is a small solar power system with μA SPCE061A microcontroller as the control core. It is mainly composed of solar panel, battery, single chip microcomputer and LED driver. It can realize real-time monitoring of battery charge and discharge and accurate A/D sampling. It ensures the timely response to the battery condition and fully guarantees the service life of the battery, thus making the system run for a long time and stably. In the system, the single-chip microcomputer detects the voltage of the solar panel at any time, and charges the battery when the predetermined value is reached. When the voltage is insufficient, it is disconnected from the battery; the single-chip microcomputer simultaneously detects the battery voltage to ensure that the battery is not overcharged or over-discharged.

At the same time, the battery supplies the power of the single chip system and the LED system. The LED is driven by the PT4115 chip, which can simultaneously drive the 30W LED lamp to work normally, and can achieve the predetermined illumination. Under normal lighting conditions, up to 12h of night illumination can be maintained. The system block diagram is shown in Figure 1.

2. 1 Control chip selection SPCE061A is a 16-bit single-chip microcomputer with high cost performance. The chip has 8 10-bit precision ADCs and two 10-bit precision DACs.

SPCE061A also integrates an ICE (in-circuit emulation circuit) interface, which makes programming and emulation of the chip very convenient, while the ICE interface does not occupy hardware resources on the chip. Users in the integrated development environment (unSP IDE) It can be used to simulate the chip; the download (program) of the program is also downloaded through this interface.

2. 2 Solar panel power determines that the load power in the system is 30W, the system requires 12 hours of night work, and the required energy is 360Wh.
The watts of the required power of the panel is 5. 3W, which is calculated according to the illumination.

2. 3 Energy storage system Small independent photovoltaic system is useful for lead-acid batteries, but also for nickel-cadmium batteries, but large and medium-sized systems generally use lead-acid batteries. Because in the independent photovoltaic system, since the output power of the solar cell varies with the sunlight intensity, when the input power of the solar cell is zero or small at night or rainy days, the load of the solar cell is not satisfied, so the independent photovoltaic system needs an energy storage device. When the light is strong, store the excess energy for use when the light is weak.

For the selection of lead-acid batteries, the main consideration is the capacity and working voltage of the battery. The capacity of the battery refers to the sum of the energy that the battery can continuously supply under certain discharge conditions. The choice of this parameter is mainly related to the average intensity of solar radiation under the working conditions of the solar photovoltaic system and the time and power required to continuously supply the load. The working voltage is the voltage that appears on the load when the battery is switched on and the load is discharged. The magnitude of the voltage is mainly determined by the rated operating voltage of the later load.

In the design of this solar photovoltaic streetlight system, it is proposed to use 12V/30W LED energy-saving lamps, so the selected battery operating voltage is 12V.

The calculation of the battery capacity is to ensure that the night illumination of three consecutive days of rainy weather can be maintained after a full-scale charging. The calculation formula is: battery capacity = daily power consumption of the load × days. The calculation of the daily power consumption of the load is: Load daily power consumption = load current × hours

2. 4 Lamp selection At present, most solar lamps use LED as the light source. The LED has a long service life and can reach more than 100000h, and the working voltage is low, which is very suitable for application in solar street lamp system. In particular, LED technology has achieved a key breakthrough, and its characteristics have been greatly improved in the past few years, and the performance price ratio has also made a big breakthrough. It has the advantages of energy saving, longevity, good color rendering and safety.

Because the working voltage of the LED street lamp is generally 12V or 24V, it is a safe voltage and can be grounded without electrical protection. However, the LED street lamp metal pole should be grounded and the grounding resistance is not more than 10Ω. As for the light pole and the lamp housing, the height of the pole should be determined according to the width of the road, the spacing of the lamps, and the illumination standard of the road. Between the aesthetics and energy saving of the lamp housing, most of them choose energy saving, and the appearance requirements of the lamps are not high, so it is relatively practical. At present, the standard of the LED street light is generally the average illumination of the uniformity of road surface illuminance of 0.48. The spot ratio is 1: 2, which is in line with road illumination. (The actual 1 /2 center spot reaches 25 LUX, the 1 / 4 center light intensity reaches 15 LUX, the lowest light intensity 4 LUX at 16 m, and the overlapping light intensity is about 6 LUX). At present, the market street lamp lens material is an improved optical material, the transmittance is ≥93%, the temperature resistance is -38 to +90 °C, and the anti-UV ultraviolet yellowing rate is unchanged at 30000h. It has very good application prospects in new urban lighting. Dimming of depth, and color and other characteristics do not change due to dimming. The power requirement of the system for the street lamp is 150W high-pressure sodium lamp illumination requirement. Based on the introduction of the advantages of the above LED lamp, and compared with the conventional lamp source, the LED lamp has a brighter application prospect. At the same time, the 30W LED lighting effect is equivalent to the 150W conventional lamp. The lighting effect of the source, for the practical application and cost consideration of the street lamp, the circuit designed by the system is intended to adopt 12V/30W LED lamp, and finally the LED with model GP-FH is adopted as the street light source of the system.

3 control circuit
3. 1 control circuit scheme The system uses PWM (Pulse Width Modulation) modulation method to control the control circuit for charging the battery. The switching device uses MOS tube. The control circuit has temperature compensation, overcharge, over discharge, load short circuit, overload protection, etc. The function greatly extends the service life of the battery and ensures the normal operation of the entire street lamp system.

3. 2 Software design The software design part is mainly the detection of the battery state, and the control scheme of the circuit is determined according to the voltage state. The LCD display program is mainly responsible for the display of a series of parameters such as current and voltage. The keyboard is controlled by a keyboard to save power. The keyboard control program uses interrupt control to ensure accurate control of the system by external operations.

Because SPCE061A can't perform multi-channel AD conversion at the same time, the program uses time-sharing method to detect and use limited resources to complete system tasks. The PWM wave is generated by Timer A according to the current parameter to accurately control the current. At low voltages, the relay is controlled by the IOB1 output level to control the output circuit.

4 Benefit Analysis:
At present, most of the street lamps are still powered by AC. On the one hand, the technology of AC circuit lights is very mature, and there are many uncertain factors in solar street lights. On the other hand, the main consideration is still that the initial investment of solar energy is too large, thus ignoring Many advantages of solar power supply. It is well known that the most important advantage of solar energy is that it is an inexhaustible and cleanest renewable energy source. It can effectively slow down the problem of global warming, and it will gradually replace some traditional energy sources. Decision makers have now realized that the replacement of high-pressure sodium lamps by LED street lamps is a trend. At the same time, solar-powered LED street lamps have also replaced the trend of AC drive.

1) The replacement of all street lights in the country into solar street lights can save the power generation of a Three Gorges hydropower station. LED street lamps are more energy-efficient than high-pressure sodium lamps and have long been recognized. However, there may be some quantitative concepts. It is now recognized that a 100W LED street light can replace a 250W high pressure sodium lamp, so it can be simply assumed that each LED street light can save 150W. However, if it is changed to solar power, then even this 100W of electricity can be saved, that is, each street lamp can save 250W. According to statistics, the total number of existing street lamps in China is about 100 million baht. If the 100 million street lamps can be converted into 60 million 盏250W high-pressure sodium lamp street lamps, and then assume that all 60 million street lamps are converted into solar LED street lamps, then a total of Save 15 million kW of power. Assuming that every street lamp works 12 hours a day, it will save 65.7 billion kWh in one year. The total power generation of the Three Gorges Hydropower Station in 2007 was 61.603 billion kWh. Therefore, the energy saved after changing all the street lamps in the country to solar street lamps will exceed the annual power generation of a Three Gorges hydropower station. This is an extremely amazing number.

2) The efficiency of solar power supply will be 15% higher than that of AC power. Because it is powered by AC, it must be converted to DC by switching power supply. The efficiency of a typical switching power supply is about 80%. So for a 100W LED street light, the AC input power will need about 120W (120W in the comparison table below). When using solar power, the DC/DC constant current source is used, and its efficiency is as high as 95%. Therefore, the total efficiency of using solar energy after totaling is about 15% higher.

3) The overall cost of solar-powered LED street lights is much lower than that of AC-powered LED street lights. The cost of LED heads and poles for both systems is roughly the same, with the main difference being solar panels. Typically, solar panels are about three times the power of LED luminaires. If the LED is 100W, then a 300W solar panel is required. At present, the price of solar panels has been reduced to below 23 yuan / W, 300W is 6900 yuan. In addition, solar systems require batteries, but their cost is equivalent to the cost of switching power supplies in AC power. So the two can be offset. Therefore, the difference in cost of the lamps themselves is mainly solar panels.

The maximum cost of an AC-powered LED street light during initial installation is the laying of the cable. It is generally believed that the cost of the cable itself is mainly, but in addition to the cable itself, its laying, auxiliary facilities (inspection wells, power distribution equipment), etc., are much more expensive than the cable itself. Now suppose that a mine entry road is taken as an example: the length is 10km and the road width is 18m. Now every 30m, the opposite side, a total of 666 盏 LED street lights are needed. If solar street lights are used, the cost can be recovered by 610,000 yuan within five years. After five years, the annual electricity bill can save 1.22 million yuan. The price of solar panels continues to drop, and the cost savings are even greater. The cost comparison of AC-powered LED street lamps and solar-powered LED street lamps is shown in Table 1.

5 Conclusion:
The paper analyzes the charging mode of the solar charging control circuit, the functional requirements of the control circuit and the practical application, completes the hardware circuit design, realizes the scientific management of the battery, and applies it to the coal entering solar street light system. in.

There are still many areas for improvement in the design of this paper. The most important one is how to maximize the efficiency of solar energy. The most important method at present is to control the position and height of the sun and the maximum power point of the solar cell. Tracking to achieve. Solar cells are devices that rely on solar radiant energy to generate electrical energy. The same solar panel has different optical radiant energy due to different angles of placement, and the generated electrical energy is different. Therefore, in order to increase the output of solar cell power, the solar panel can be automatically tracked according to the change of the orientation and height of the sun in the sky; in order to maximize the output power of the solar cell, in addition to the technology of using solar height and azimuth tracking, There is also a solar cell maximum power point tracking. Due to the non-linear characteristics of the PV array's output characteristics, it must be considered that the photovoltaic system can work at or near the maximum power point of the PV array output characteristics under different sunshine, temperature and different load characteristics, so as to fully utilize the solar energy absorbed by the solar array. .

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