How much do you know about the configuration of solar LED street lights?

How much do you know about the configuration of solar LED street lights?

At present, the most widely used products in China’s photovoltaic small and micro power systems are LED street lights, garden lights, lawn lights, landscape lights, roadway lights, traffic lights, beacon lights and portable energy-saving lighting devices that use solar photovoltaic cells as energy sources. Various types of photovoltaic power utilization devices. The photovoltaic power generation of this type of lighting device is generally between 1W-200W, and the light-emitting components are basically LED lights. The so-called LED (Light-Emitting-Diode) lamp is a “light-emitting diode”, and its light-emitting principle is different from the commonly used incandescent lamps, tungsten lamps and energy-saving lamps with three primary color powders. “Electroluminescent solid-state semiconductors” that convert to visible light.

The spectrum of LED lights is almost all concentrated in the visible light band, which can radiate various colors and white light, without ultraviolet (UV) and infrared (IR) radiation output; its luminous efficiency can reach 80%-90%, which is a high-brightness point light source. The LED lamp is shock-resistant, anti-vibration, highly reliable, low maintenance cost, driven by a voltage regulator, and its working life has nothing to do with the grid voltage; Layer damage and failure: so “heat dissipation” is the primary problem of LED lamps. For high-power LED lights, as long as the operating temperature is well controlled, its lifespan can reach more than 50,000 hours.

Solar LED street light is composed of encapsulated solar photovoltaic cell (panel) components, LED lighting fixtures, batteries, electronic controllers (including charge and discharge controllers, light control and time control; or electronic switching systems with time-based power control) and Light poles, etc.; miniature solar photovoltaic power generation-storage-supply and power consumption systems (devices) combined with five components. Figure 1 is a structural diagram of a basic solar street light system.

Figure 1 – Block diagram of solar street light structure

If we want to design or install an LED street light, the first thing we need to confirm is “where is the street light installed”? It is necessary to propose the preliminary design requirements for the configuration of the street light system according to the installation and use conditions such as the width of the road width of the installation site, the traffic flow and the illuminance required for lighting. The key to determining the illuminance of LED lights is the power of the lighting components; in addition, there are related factors such as the height of the pole and the distance between the poles. A few years ago, when the Kunming Science and Technology Bureau carried out the “Green Lighting Project” in Kunming, in order to help the counties and towns to correctly select the power and illuminance of LED street lights, they organized the municipal street lighting management department and experts in solar energy to discuss together. A technical specification for solar street lights in Kunming has been formulated.

According to this “standard”: the main road with a road width of 8m-12m, the lighting components can be configured with a maximum of 100W light source, and the solar street light in the 12h lighting period: the secondary road with a road width of 5m~9m, the light source power is configured according to 60w/2h: For secondary roads or rural roads of 5m-7m, the light source power is configured according to 30W/12h; or 20W/12h; as for garden lights, lawn lights, landscape lights, and roadway lights in residential areas, solar energy is generally configured according to 4W/12h lighting requirements The power consumption of LED street lights.

After determining the power consumption required for the illumination of the LED street light, we also need to base on the meteorological conditions and geographical latitude of the installation site of the street light. Through the comprehensive balance, the generated power of the solar photovoltaic cells that the system needs to be configured is finally determined. In general, after determining the power (Pi) of the solar street lamp: the daily working time of the street lamp (hi), we can calculate the daily load power (Li) required by the solar street lamp on a certain day according to the formula: Li=ΣPihi; Then according to the daily average solar irradiation hours (HL) of the installation site; and the relevant selected empirical coefficients, such as: controller power loss coefficient (1.05); photovoltaic module system loss coefficient (0.55); the following empirical formula can be used (Fig. 2) Calculate the power generation (L) of the required solar cell modules:

Why is it necessary to multiply a 1.05 controller power loss coefficient on the basis of the average load daily power of solar LED street lights? This is because: first, the automatic controller system of solar LED street lights also consumes energy in the uninterrupted program control work around the clock; second, there is also an efficiency loss during the charging and discharging process of the system controlled conversion. Accordingly, we estimate its “empirical data” to account for about 5% of the total system labor consumption.

As for the denominator part of the formula (Fig. 2), why should the system loss coefficient of photovoltaic modules be set to 0.55? It is due to the safety precautions that have to be taken for the following series of influencing factors that may affect the power generation of the system:

First, silicon solar cells have an obvious negative temperature effect when generating photovoltaic power under sunlight; that is, as the temperature of the solar panel increases, the open-circuit voltage will decrease significantly with the increase of light intensity, that is, power generation. Efficiency decreases as the temperature of the solar panel itself increases.

Second, the power generation capacity of solar cells is related to the solar radiation intensity that can be received; generally, solar panels that are installed at an angle are fixed, and the solar radiation intensity that can be received varies greatly in different seasons within a year. It may be fully calculated, so the possible losses due to changes in solar radiation intensity must be deducted.

Third, in the system combination and daily operation of solar cell modules, there are several environmental factors and system matching losses: including the loss of solar radiation caused by dust and haze generated by the external environment; In addition, there must be a certain margin for system security; all in all, it is necessary to ensure the long-term safe and normal operation of the system without causing a substantial increase in costs. After synthesizing various influencing factors, classical data collection calculation and case analysis, 0.55 is selected as the system loss coefficient of photovoltaic modules based on empirical data.

The above “empirical data” can be provided for reference applications of small power supply systems that are used in street lamps and do not require very strict system configuration accuracy.

After the matching power generation of solar cells is selected, the functional components closely related to this need to be considered, that is, the energy storage device of the system – the battery pack. All the electric energy produced by the solar cell modules during the day is effectively stored. In addition to meeting the premise of lighting at night, it is also necessary to reserve enough energy to meet the requirements of the longest continuous cloudy and rainy days in the future according to the stability rate of the local sun. required power. Therefore, the capacity of the battery is too small; but the capacity of the battery is too large, so that it is always in the “over-discharge” working state of power loss, which will also affect the service life of the battery. Moreover, the selection of an excessively large battery will also cause inconvenience. Necessary cost wasted.

The capacity of the battery should match the power generation capacity of the solar cell and the electricity load of the street lamp for several consecutive days. Under normal circumstances, the capacity of the battery we choose should be about 6 times the daily power consumption of the street lamp. That is, when the battery is fully charged at one time, it can ensure the lighting power consumption of the system for 5 to 7 consecutive rainy days and nights. All in all, we require the battery configured for the street lamp: the self-discharge rate should be low, the deep discharge capacity should be strong; the charging efficiency should be high, There can be no memory effect; the operating temperature range should be wide; the battery life should be long; the price should be cheaper. What capacity (M) battery does the specific system actually need to configure? According to the formula (Figure 3), the calculation selection can be made:

In the formula: M——battery capacity
P1—the power of lighting street lamps
hi—street light daily working hours
d—the maximum number of consecutive rainy days at the installation site of the street light;
V—battery rated voltage:
1.1—The battery needs to increase its capacity by 10% as an insurance factor;

C—the maximum discharge depth of the battery, generally the battery is 50%-80%; we take 70%.
In order to ensure the performance and service life of the battery, for solar street light products, we prefer to use colloidal sealed lead-acid batteries. Because the electrolyte of this colloidal battery adopts fumed silica; the separator adopts advanced PVC-SiO2 colloidal battery special separator. The colloidal sealed lead-acid battery has the functions of waterproof, moisture-proof, anti-corrosion, thermal insulation and ventilation. The operating temperature range is -20°C-55°C: good low temperature performance, discharge at low temperature -20°C (60% C10), the discharge capacity of the colloidal energy storage battery is 80% of the normal temperature capacity. The high temperature characteristics are stable and can meet the requirements of high temperature environment of 55 °C. The service life of charge and discharge cycles is as long as 2000 to 3000 times, and there is no memory effect. The average service life of colloidal sealed lead-acid batteries can reach more than 5 years.

For the same level of solar LED street lights, only solar cells or batteries with the same power generation and capacity; it is almost impossible to distinguish the level of technical performance; the core component that can effectively distinguish the performance of solar street lights is the controller.

Solar charge and discharge controllers generally use single-chip microcomputers to achieve charge and discharge protection of batteries. The basic functions of the controller include: overcharge protection, overdischarge protection, light control, induction control, anti-reverse connection, charging trickle protection, undervoltage protection, overvoltage protection, short circuit protection, waterproof protection, etc. When no one or a car passes, the controller can automatically reduce the power to less than 50%; or control it through a time program, and within 1h~2h before entering the midnight to the sunrise, the street lamp works in half-power state to save energy. The chip control system of street light control appliances has a shielding device inside; it is generally installed in the light pole at the bottom of the light pole, and is fully sealed to prevent moisture and theft; the controller works continuously for 24 hours, and its own power consumption is less than the rated power 5%; service life of more than 10 years. To choose a controller with higher charging efficiency, it should have the MPPT function that automatically tracks the maximum power output of photovoltaic modules.

Due to the relatively harsh working environment of street lamps, they must be placed in the wilderness all year round, and subjected to the test of wind, sun, rain and ice, snow and frost. , to have more stringent requirements. Conical single curved arm light pole, the material is generally Q235 carbon steel: wall thickness ≥ 4mm, top diameter 60mm, bottom diameter 154mm, light pole chassis thickness 22mm; no cracks, pores, undercuts, incomplete welding and other defects on the surface of the weld ; The width of the weld is 4mm~9mm, and the height of the reinforcement of the weld is 0mm~3mm; the lamp pole is hot-dip galvanized with anti-corrosion treatment on the inner and outer surfaces, in line with the GBT3912-92 standard, and the zinc layer on the galvanized surface should be uniform, smooth, free of burrs, For drip tumors and excess agglomeration, the zinc layer should be firmly combined with the steel rod, the zinc layer should not peel off, not bulge, and be smooth and beautiful; the thickness of hot-dip galvanizing should be 65μm~90μm. After hot-dip galvanizing, it is generally necessary to spray plastic. The spray powder should be used for outdoor special powder, and the coating should not be peeled off or cracked. After spraying, the anti-corrosion performance of the steel pole can be improved, and the aesthetics and decoration of the lamp pole can be greatly improved. The color can also be selected in a variety of ways; the service life of the street lamp pole is generally required to reach more than 20 years.

The biggest difference between solar LED street lights and general street lights is that there are 1 to 2 large-area solar panels installed at the top of the pole anchored at the top of the pole. While increasing the wind resistance of the system, the components of the whole pole will also follow the wind direction. From the normal stress state, various nonlinear stress changes occur.

For example: the solar panels installed obliquely in the south will generate upward lift when the north wind blows; and when the south wind blows, it will generate a great reverse pressure; these forces increase with the length of the light pole, which will affect the foundation of the light pole. In different directions, it will produce a great overturning destructive force; the higher the light pole, the longer the force arm, and the greater the prying moment. Therefore, when designing and constructing street lamps, it is necessary to carry out careful wind resistance design for the maximum seasonal gust that may occur locally, possibly to the strength of the support system of solar panels and lighting fixtures and the embedded foundation of light poles. In order to ensure the absolute safety of the street light system. In addition, since street lamps are metal objects that exist independently in the wild, effective lightning protection measures must be taken for electrical equipment such as metal lamp poles, solar cell components, lamp brackets, and metal chassis: the connection of the grounding body should be welded firmly, and necessary Anti-corrosion treatment; when the ground wire connected to the electrical equipment cannot be welded, it should be connected with galvanized bolts to ensure that the entire system is in a reliable lightning protection grounding protection state.

The anti-theft treatment of solar LED street light control box and battery pack is an indispensable and important part. It is an effective anti-theft measure to bury the control box and the battery pack in the ground and pour it with cement, and it can also play the role of constant temperature protection. However, such anti-theft measures have advantages and disadvantages, because no matter what advanced technology we adopt to prolong the service life of the battery, we cannot make the battery and other components of the street lamp have the same lifespan. During the whole life of the street lamp, it is necessary to update the battery more than 2 to 3 times, which is an unavoidable problem. This contradiction needs to be further developed and innovated, and be seriously reflected and implemented in the system design and construction, otherwise there will be endless troubles.

It should be said that the biggest problem in the use of small and micro photovoltaic appliances such as solar LED street lights and garden lights is the life of the battery. Generally, the normal service life of lead-acid batteries is 3 years to 5 years; the advantage of lead-acid batteries is that floating charge has no memory effect, but excessive charging or discharging will accelerate the loss of the battery. Lead-acid batteries have a wide range of adaptability. Although the system can work under the conditions of -40℃~60℃, in fact, only when the temperature is constant below 50℃, the service life of lead-acid batteries can be extended accordingly. Lead-acid batteries are inexpensive, but still have a shorter overall lifespan than cadmium-nickel and iron-nickel batteries. To this end, in line with the principle of saving electricity, it is necessary to automatically control the time and brightness of street lighting (power consumption) and the ambient temperature of the battery working: to protect and prolong the service life of the battery as much as possible, It has become the focus of photovoltaic application enterprises to exert their professional expertise, show their magical powers, and compete in the product market. In this regard, Kunming Tuori and Kunming Interpretation Co., Ltd., based on their own technical strength, took corresponding measures and achieved good results. Kunming Tuori uses computer chips to specially design and develop the state data storage function of the solar DC street light system controller.

The controller adopts tact switch, easy to complete all operations and settings. The controller has short-circuit, overload, unique anti-reverse protection, full-charge, over-discharge automatic shutdown, recovery and other full measures; as well as detailed charging instructions, battery status, load and various fault instructions. The controller samples the battery terminal voltage, discharge current, ambient temperature and other parameters related to the battery capacity and service life through the computer chip, and calculates through the special control number model to realize the discharge rate and temperature compensation and correction in line with the characteristics of the battery. High efficiency, high efficiency Accuracy control, and high-efficiency PWM battery charging mode is adopted to ensure that the battery works in the best state for a long time, so as to greatly prolong the service life of the battery.

The controller has a variety of working modes and output mode options, which can meet the various needs of users and the storage function of data status. Intelligent detection and data storage of battery voltage and current when the switch state of the street light changes: the daily charge and discharge of the solar street light system, extreme voltage and current records and other state data collection and storage; the collection and storage of the above data, the fault identification and stability of the street light Sexual determination provides powerful analytical data. The controller is equipped with a convenient output interface, and can use the RS232 and USB interfaces to read data on site for quick analysis. In addition to taking technical measures to greatly prolong the deep cycle of the battery, Kunming Chuanyi also introduced nanotechnology into the battery to make it breathable and waterproof. The anti-theft safety is effectively achieved, and the working temperature of the battery is stabilized in the best state of 20 ° C ~ 25 ° C for a long time, thereby effectively prolonging the service life of the lead-acid battery.

It can be said that the current competition in the street lamp market is nothing more than: first, the protective extension of the life of the lead-acid battery; second, the intelligent monitoring and maintenance of the control system; of course, it also includes perfect and timely after-sales service. We have long said that due to the particularity and harshness of the working environment of solar equipment, any solar equipment has the problem of “three-point construction and seven-point management”: after the street lights are lit, after-sales maintenance and maintenance services for several years. In this long period of responsibility, every manufacturer of solar photovoltaic application equipment is also faced with the test of excellent product quality and severe after-sales service reputation; whoever can obtain an innovative credibility record in this regard can account for Take the lead in a large market with inexhaustible product demand.

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