Research and Application Analysis of Solar LED Street Light System

LED semiconductor lighting Reuters With the improvement of the quality of human life, the consumption of energy has also increased rapidly, the depletion of oil resources, the Earth's ecological environment is deteriorating, lack of energy and environmental pollution has become an important issue facing the sustainable economic development, causing People's widespread concern.

According to relevant statistics, lighting accounts for about 20% of global energy consumption. China's annual electricity for lighting is more than 300 billion degrees, of which road lighting accounts for about 30% of total lighting. The effective use of natural energy is the focus of technology research. By effectively collecting and recycling solar energy, it can save nearly 1/3 of lighting power every year, equivalent to the annual power generation of the Three Gorges Project with a total investment of more than 200 billion yuan.

Some barren areas are still using non-renewable candles, wood and kerosene lamps and other biofuels to illuminate, effectively utilizing the characteristics of solar energy sources without pollution and never exhausting, combined with LED lighting, high efficiency, energy saving, environmental protection, long life and easy control of light color. Through the application of solar LED street lamps to improve energy efficiency and ease the energy crisis, and promote the development of China's energy reuse technology, it is of great significance to improve lighting quality and adjust the social and economic structure.

1. Solar LED street lighting system

1.1 Solar LED street light scheme

Solar LED street lights are made up of solar cells (physically called photovoltaic photovoltaics, PV), wind turbines, storage batteries, controllers, inverters, LED street lights, mounting brackets and lights The components such as poles are divided into wind-solar complementary, commercial complementary and independent types according to the structural combination.

Constrained by factors such as distribution density, illumination time, continuous cloudy weather and snow and rain weather, the PV or battery capacity is usually accurately calculated, and the complementary lighting or power supply is used to ensure the lighting requirements of the project.

Shenzhen Spike Optoelectronics Technology Co., Ltd. has accumulated years of experience in the project and developed independent solar LED street lights as shown in Figure 1. The products are not affected by geographical restrictions and power installation conditions, and there is no need to excavate the road surface for wiring and pipe construction. It can be adjusted according to the geographical conditions. The battery and controller are installed in the box and fixed on the pole. The controller can also be installed in the inspection port at the bottom of the pole and buried in the battery.

Figure 1 independent solar LED street light

1.2 Product Standard

Checking the current standards in China, the safety of solar LED street lamps should meet the requirements of GB 24460-2009 "General Technical Specifications for Solar Photovoltaic Lighting Devices". The overall structure has sufficient strength to withstand 10 wind load tests. The protection level is not less than IP54, 4m or more. The height of the pole should have good lightning protection and grounding protection measures. The grounding resistance should be less than 30 Ω. The insulation resistance between the charged body and the metal parts should be greater than 2 MΩ. The cabinet should be designed to be opened with special tools.

When designing or determining the product, the components shall meet the requirements of the corresponding national standards. When there is no corresponding national standard, it shall be implemented in accordance with IEC standards, industry standards, alliance standards or enterprise standards to ensure that the safety and performance of the products meet the standard requirements.

PV should meet the requirements of GB/T 9535-2006 "Design and Identification of Crystalline Silicon Photovoltaic Modules for Surfaces". Fixed-type valve-regulated lead-acid batteries should meet the corresponding requirements of GB/T 19638 series standards, general-purpose valve-regulated lead-acid batteries. Should comply with the corresponding requirements of GB/T 19639 series standards, controllers and inverters should meet the requirements of GB/T 26849-2011 "Performance Requirements for Electronic Control Devices for Solar Photovoltaic Lighting", LED street lamps should meet the requirements of GB 7000.1 and GB 7000.5 Parts such as poles and mounting brackets shall comply with the requirements of Article 6.5 of the GB 24460-2009 standard.

1.3 Solar cells

PV is a kind of optoelectronic semiconductor component that converts light energy into electric energy through photoelectric effect or photochemical effect, and can output voltage and generate current when there is a certain light, and has certain anti-corrosion, rainproof and anti-icing And wind resistance.

According to the crystal state, PV can be divided into two types: crystalline thin film type and amorphous thin film type. The former is divided into single crystal silicon and polycrystalline silicon. The conversion efficiency of industrialized N type single crystal PV is about 21%-24%, P type. The conversion efficiency of single crystal PV is about 18.7% - 19.2%, and the conversion efficiency of polycrystalline PV is about 17% - 17.5%. The newly developed ultra-efficient silicon PV of the University of Delaware uses a new type of lateral optics. The focusing system increases the conversion efficiency to 42.8 %, which is about 1 times higher than the P-type single crystal PV.

PV open circuit voltage, short circuit current, maximum output power, fill factor and conversion efficiency are the benchmarks for measuring performance. To prevent the hot spot effect of the shielded PV in the series, a bypass is connected in parallel between the positive and negative electrodes. The diode prevents the energy generated by the light-receiving component from being consumed by the shielded PV.

1.4 Battery

As the energy storage unit of the solar LED street lamp, the PV converts the received effective light energy into a power input battery for storage, and supplies power to the LED street lamp when the lighting needs.

Generally, the single battery has protection against overvoltage, undervoltage and overtemperature, as well as protection functions such as overcharge, overdischarge and overcurrent. When charging, the internal active material of the battery is regenerated (storage energy is stored as chemical energy), and when it needs to be discharged, Convert chemical energy into electrical energy.

From the point of view of the use and maintenance cost, the sodium-sulfur battery needs continuous heating, and the vanadium redox flow battery needs fluid control, which undoubtedly increases the cost, and the two kinds of batteries are not industrialized, and the lithium-ion battery has Strong competitiveness but expensive, almost no maintenance advantage is widely used in high-end projects. According to the current status and cost considerations of solar LED street lamps at home and abroad, the solution usually uses a cost-effective and maintenance-free lead-acid battery. The brand lead-acid battery has a service life of about 3 years under frequent charge and discharge.

1.5 controller

The controller is the core component of the solar LED street lamp. On the one hand, it controls the charging and discharging of the battery to protect the battery from overcharging. On the other hand, according to the change of the solar receiving intensity and the load of the PV, the working mode of the battery pack is switched and adjusted, and the battery is replaced. The constant current of the electrical energy is distributed to the load LED lamp.

The controller plays a key role in the continuity and stability of the system operation and should comply with the current national standard GB/T 26849 for low power consumption requirements that the maximum no-load current should not exceed 1% of its rated current. The controller and coordinator with intelligent control function use wireless communication (WC) or power line carrier (PLC) technology to form a system network, real-time control of LED street lights and environmental conditions, and data analysis and processing, and According to the LED street lamp and electric energy status, the control command is sent to realize the intelligent monitoring and control of the illumination and electric energy distribution after the LED street lamp is set up, and the current situation of the discrete independent control of the solar LED street lamp is changed. The system using the wireless networking and the intelligent control is shown in FIG. 2 .

Figure 2 Solar LED street light system

(1) Operation processing: The controller uses an advanced RISC machine (ARM) to perform operational analysis on the data transmitted by the acquisition module and issue appropriate decision commands. ARM's charge and discharge control between the battery and the PV, when the PV can not normally supply power to the load, maintains the stability of the power supply to the load through the charge and discharge and power supply switching, voltage regulation, short circuit protection and soft start control on the controller. The control center will master the operating status of all terminals in the system, and can use the remote control to set various operating modes and data.

(2) Control data acquisition: The data acquisition of the controller includes the collection of the working state of the PV, the storage data of the battery, and the working status data of the LED street lamp. The controller's acquisition module collects voltage, current, temperature, and ambient illumination in real time and provides it to the microprocessor for computational analysis and processing. The circuit of voltage and current acquisition is controlled by the ARM processor, which can control the equalization circuit to enter the working state. The important data such as system operation mode and parameters can be saved in the data storage, and will not be lost after power failure.

(3) Load control: The controller controls the LED street lamp to control the brightness of the time zone to achieve the second energy saving. The system designs multiple load outputs, and the output of the circuit has independent control and detection functions. When P0.6=1, the triode is turned on and the relay is closed. When the MOS tube is turned on, the battery supplies power to the LED street light. When the night is controlled after 12 o'clock. The LED street light is reduced by half, and when the PV output voltage is higher than 8 V (according to the project requirements), the controller cuts off the power supply to the LED street light.

(4) Charge and discharge control: The controller controls the charging current according to the level of the battery voltage and whether it supplies power to the LED street lamp, ensures that the battery is full, and prevents the battery from overcharging, over-discharging and reverse charging to the PV at night. The controller uses the maximum power point tracking (MPPT) to quickly charge the battery. At startup, the MPPT control output is fixed at a fixed duty ratio D=1/2, and the output frequency is 200 K. The detection method changes the duty ratio by a fixed step. When the input power rises, the duty cycle continues to increase. When the power decreases, the duty ratio is reduced to find a neighboring point, and the step size is adjusted according to the rate of change of the power. The direct current generated by the PV is efficiently stored in the battery. The anti-back-charge Schottky diode is also arranged in the control circuit. When the PV voltage is lower than the battery voltage, the battery is prevented from being reversely charged to the PV, and the circuit is automatically disconnected to protect the battery when the battery is reversely connected.

1.6 LED street light

LED street lamp energy consumption is one of the important factors affecting system efficiency. With the advancement of technology, LED has exceeded 160 lm/W light effect. According to typical road lighting requirements, the lens is designed to have large angle, wide angle of view and batwing shape. The secondary optical light distribution system fully meets the lighting quality requirements of CJJ 45-2006 "Urban Road Lighting Design Standard". The LED street light adopts the fin natural convection heat dissipation structure design, so that the air flows through the heat sink ventilation channel to improve the heat dissipation of the LED module. The efficiency, waterproof and dustproof level of IP67 independent module LED street light is shown in Figure 3. The modular design of the product improves the reuse rate of key parts and is suitable for mass production.

Figure 3 LED street light

1.7 Light pole and structural parts

Solar LED street lamps may be used for a long time in coastal areas with high humidity and high salt content. The structural parts such as poles and mounting brackets should be made of Q235 steel. The surface is hot dip galvanized and then powdered to ensure that it can pass at least 72 h of salt. The fog test meets the warranty period of 5 years or more for outdoor use. Hot dip galvanizing shall comply with the requirements of national standard GB/T 13912-2002 "Technical requirements and test methods for hot-dip galvanizing of metal-clad steel parts", if the wind-proof coefficient of the lamp post and the bracket is selected to be 27 m/s ( Corresponding to the 10th typhoon), its structural design should be able to withstand the windward pressure of 2700 Pa, while considering the snow load and the need to withstand mild earthquakes. In addition, the PV mounting bracket should be designed for optimal tilt angle and adjustable structure in any direction to ensure maximum utilization efficiency of solar LED street lights.

2. Technical difficulties

2.1 Energy complementarity

In practical applications, due to the influence of natural conditions, a certain solar LED street lamp is in the shade or cloud cover for a long time.

The battery will be under voltage and cause the LED street light to illuminate to affect the lighting. Figure 4 Energy Complementary Solution In each LED street light, an intelligent control module is configured, and the LED street light is managed by WC or PLC technology. The coordinator sends the operation information of all LED street lights to the remote monitoring platform through various communication methods. After obtaining the energy balance control information of a certain two LED street lamps, the system sends an energy balance control signal to the relevant measurement and control module through the ZigBee wireless network intelligent management function, and the corresponding measurement and control module receives the command and then starts. Two power MOS tubes are connected to charge the high-capacity battery to the low-battery battery to achieve an intelligent management mode that fully and reasonably distributes energy, real-time monitoring and data collection and analysis of each LED street lamp, and solving the LED street light in the system. The allocation of electrical energy differences.

Figure 4 Regional Complementary Schematic

2.2 Specific sunshine

Because solar energy resources are affected by geographical environment and climatic conditions, solar energy resources are different in different regions, and accurate system configuration calculation is a key point in the design of solar LED street lamp control system. Therefore, Spike Optoelectronics has accumulated solar power through project experience. The calculation method of the system matching gives a formula for calculating the power generation amount more in line with the actual application.

The system uses the solar radiation meteorological data of the region to calculate the power generation of the PV group in 12 months, and performs system matching calculation with the energy balance of 12 months of the whole year to avoid the error introduced by human interpolation or discrete data, and build PV and control. Solar LED lighting system consisting of a battery and a battery.

The controllers are connected in a wireless manner, and a wireless data collection platform is built. The system data is used to complete the optical data collection by cycle. According to the data analysis, the power generation power distribution curves under different illumination conditions are plotted, and the corresponding software is configured to accurately evaluate the project. [6]

2.3 Battery Optimization

When the battery is in a low battery state for a long time, it will cause irreversible capacity drop. Usually, the controller adjusts the charge and discharge time to ensure the service life by detecting the internal resistance of the battery, but the internal resistance of the battery changes with the capacity. Large differences often affect the accuracy of the measurement results.

The test proves that the controller has two storage units of current and voltage, record the current and voltage of charge and discharge at any time, and detect the capacity of the battery by means of integration. The deep cycle charge and discharge once every three months, the controller on the battery The actual capacity is corrected and adjusted, and different control modes are adopted according to the working state of the battery. When the voltage is lower than the lower limit, the protection mode is directly entered or the output power is adjusted to protect the battery.

2.4 Reliable operation

The components of solar LED street lamps are made of high-quality industrial-grade components and manufactured according to strict production processes, which are suitable for reliable operation under harsh conditions. The controller is equipped with dedicated remote monitoring software and remote control, which can set and modify the operating mode according to the current geographical environment. The controller has perfect protection function to prevent PV reverse connection and overcharge, discharge and reverse connection of the battery. , load short circuit overload, lightning protection, etc. At the same time, the PV is controlled to safely and efficiently charge the battery, and an adaptive constant current output is provided for the LED street lamps with different characteristics.

3. Marketing and application

The distribution of solar energy resources is closely related to the altitude, geographical conditions and climatic conditions of various regions. China is one of the countries with abundant solar energy resources. The total radiation is about 930-2330 MJ/m2, and the total area of ​​the country is 2/3. The annual sunshine time in the above areas is greater than 2000 h. In most places, more than 2/3 of the weather in the whole year can use solar energy.

The sustainable use of green and environmentally-friendly solar energy resources, together with the energy-saving and environmental protection of LEDs , and the independent solar-powered LED street lamps, do not require wire-laying and other features, and have significant energy-saving and emission-reducing effects, and have been widely used at home and abroad.

Solar LED street lamps are receiving more and more applications and attention. The characteristics of high efficiency and energy saving and green environmental protection will become the best choice for more urban road reconstruction and expansion projects. They are good in remote areas such as squares, campuses, parks, streets and power shortages. Promotion and application space.

In December 2015, Spike Optoelectronics undertook 2000 sets of solar LED streetlight projects donated by the Chinese government to Antigua and Barbuda. Figure 5 shows China’s Ambassador to Antigua and Barbuda, Prime Minister of Antigua and Barbuda. Representatives of Gaston Brown and Spike Optoelectronics President Wu Feng attended the handover ceremony of the project. Antigua and Barbuda Prime Minister Gaston Brown said that more energy-efficient solar LED lighting products will be introduced and strengthened with China. Cooperation in the use of green energy.

Figure 5 China's donation ceremony for solar LED street lights in Antigua and Barbuda

Conclusion

Recycling of renewable energy is the benchmark for energy conservation and emission reduction. It is also an important measure for China's new energy industry to implement the national policy. While actively promoting the application of solar LED street lamps, it should combine the local solar energy resources and design the system according to the working characteristics and operating rules of PV. Avoid that the system does not function as expected. China is a densely populated energy-consuming country. It should combine the structural hardware and control software of the project plan to properly optimize the design in combination with the seriousness of the current energy problem. Use intelligent control technology to optimize control management to achieve secondary energy conservation and promote new energy and The application of renewable energy.