Working Principle of Solar LED Street Light

Working Principle of Solar LED Street Light

This article introduces the working principle of solar LED street lights in detail and deeply analyzes the problems and solutions of each part. I believe it will be of great help to those who want to understand LED solar street lights.

1. System Introduction

1.1 Introduction to the basic components of the system

The system consists of a solar cell assembly (including a bracket), an LED lamp holder, a control box (with a controller and a battery inside) and a lamp pole. The solar panel has a luminous efficiency of 127Wp/m2, which is highly efficient and is very beneficial to the system's wind-resistant design. The lamp holder is composed of 1W large white light LED particles or small white light LED particles, which are integrated on a printed circuit board and arranged in a dot matrix with a certain spacing as a planar light source.

The control box is made of stainless steel, which is beautiful and durable; maintenance-free lead-acid batteries and charge-discharge controllers are placed in the control box. This system uses valve-controlled sealed lead-acid batteries, which are also called "maintenance-free batteries" because they require little maintenance, which helps reduce system maintenance costs; the charge-discharge controller is designed with both full functions (with light control, time control, overcharge protection, over-discharge protection, and reverse connection protection, etc.) and cost control, achieving a high cost-effectiveness.

1.2 Working Principle

The working principle of the system is simple. The solar cell is made by the principle of photovoltaic effect. During the day, the solar panel receives solar radiation and converts it into electrical energy output, which is stored in the battery through the charge and discharge controller. At night, when the illumination gradually decreases to about 10lux and the open circuit voltage of the solar panel is about 4.5V, the charge and discharge controller detects this voltage value and acts, and the battery discharges to the lamp head. After the battery discharges for 8.5 hours, the charge and discharge controller acts and the battery discharge ends. The main function of the charge and discharge controller is to protect the battery.

2. System design ideas

Compared with general solar lighting, the design of LED solar street lights has the same basic principles, but there are more aspects to consider. The following will take the solar LED high-power street light of Hong Kong Zhenmingli Group Co., Ltd. as an example and analyze it in several aspects.

2.1 Solar cell module selection

Design requirements: In Guangzhou area, the load input voltage is 24V and the power consumption is 34.5W. The daily working hours are 8.5h, and the continuous rainy days are guaranteed to be 7 days.

⑴ The average annual radiation in Guangzhou over the past 20 years is 107.7Kcal/cm2. After simple calculation, the peak sunshine hours in Guangzhou are about 3.424h;

⑵ Daily power consumption of load = = 12.2AH

⑶ The total charging current of the solar panel required = 1.05×12.2×÷(3.424×0.85)=5.9A

Here, the designed shortest number of days between two consecutive rainy days is 20 days, 1.05 is the comprehensive loss coefficient of the solar cell module system, and 0.85 is the battery charging efficiency.

⑷ The minimum total power of solar panels = 17.2×5.9 = 102W

The use of standard battery modules with a peak output power of 110Wp and a single 55Wp should be able to ensure the normal operation of the street lighting system in most cases of the year.

2.2 Battery selection

The calculation of battery design capacity is simpler than the peak wattage of solar panels.

According to the above calculation, the load daily power consumption is 12.2AH. When the battery is fully charged, it can work continuously for 7 rainy days, plus the work of the first night, the battery capacity is:

12.2×(7+1) = 97.6 (AH), choosing two 12V100AH ​​batteries can meet the requirements.

2.3 Solar cell module support

2.3.1 Inclination design

In order to allow the solar cell module to receive as much solar radiation as possible throughout the year, we need to select an optimal inclination angle for the solar cell module.

In recent years, there have been many discussions on the optimal tilt angle of solar cell modules in some academic journals. The street lamp is used in Guangzhou. Based on the information in the relevant literature [1], the tilt angle of the solar cell module bracket is selected to be 16 degrees.

2.3.2 Wind resistance design

In the solar street light system, one of the structural issues that needs to be paid great attention to is the wind resistance design. The wind resistance design is mainly divided into two parts, one is the wind resistance design of the battery component bracket, and the other is the wind resistance design of the light pole. The following is an analysis of the above two parts respectively.

⑴ Wind resistance design of solar cell module support

According to the technical parameter data of the battery module manufacturer, the windward pressure that the solar cell module can withstand is 2700Pa. If the wind resistance coefficient is selected as 27m/s (equivalent to a level 10 typhoon), according to non-viscous fluid mechanics, the wind pressure that the battery module can withstand is only 365Pa. Therefore, the module itself can fully withstand a wind speed of 27m/s without being damaged. Therefore, the key consideration in the design is the connection between the battery module bracket and the light pole.

In the design of this street lamp system, the connection between the battery assembly bracket and the lamp pole is designed to be fixed with bolt rods.

⑵ Wind resistance design of street light poles

The parameters of the street light are as follows:

Solar panel inclination angle A = 16o Light pole height = 5m

The design selects the bottom weld width of the lamp pole δ = 4mm and the bottom outer diameter of the lamp pole = 168mm

The surface where the weld is located is the failure surface of the lamp pole. The distance from the calculation point P of the resistance moment W of the failure surface of the lamp pole to the line of action of the solar panel load F on the lamp pole is PQ = [5000+（168+6）/tan16o]× Sin16o = 1545mm = 1.545m. Therefore, the moment of wind load on the failure surface of the lamp pole is M = F×1.545.

According to the design maximum allowable wind speed of 27m/s, the basic load of the 2×30W double-lamp solar street light panel is 730N. Considering the safety factor of 1.3, F = 1.3×730 = 949N.

Therefore, M = F×1.545 = 949×1.545 = 1466N.m.

According to mathematical derivation, the resistance moment of the circular failure surface is W = π×(3r2δ＋3rδ2＋δ3).

In the above formula, r is the inner diameter of the ring and δ is the width of the ring.

Failure surface resistance moment W = π×(3r2δ＋3rδ2＋δ3)

=π×(3×842×4+3×84×42+43)= 88768mm3

=88.768×10－6 m3

Stress caused by moment of wind load on failure surface = M/W

= 1466/（88.768×10－6） =16.5×106pa =16.5 Mpa＜＜215Mpa

Among them, 215 Mpa is the bending strength of Q235 steel.

Therefore, the weld width selected in the design meets the requirements. As long as the welding quality can be guaranteed, there will be no problem with the wind resistance of the lamp pole.

2.4 Controller

The main function of solar charge and discharge controller is to protect the battery. The basic functions must include overcharge protection, over-discharge protection, light control, time control and reverse connection protection.

The general parameters of the battery overcharge and over-discharge protection voltage are shown in Table 1. When the battery voltage reaches the set value, the circuit state changes.

In terms of device selection, there are currently microcontrollers and comparators. There are many solutions, each with its own characteristics and advantages. The corresponding solution should be selected based on the needs of the customer group. I will not go into details here.

2.5 Surface treatment

This series of products adopts new electrostatic coating technology, mainly FP professional building materials coating, which can meet customers' requirements for product surface color and environmental coordination. At the same time, the product has high self-cleaning properties, strong corrosion resistance, and aging resistance, and is suitable for any climate environment. The processing technology is designed to be coated on the basis of hot-dip galvanizing, which greatly improves the product performance and meets the most stringent requirements of AAMA2605.2005. Other indicators have reached or exceeded the relevant requirements of GB.

3. Conclusion

The overall design basically takes all aspects into consideration; the peak wattage selection design of photovoltaic components and the battery capacity selection design adopt the most common design method at present, and the design concept is relatively scientific; the wind-resistant design is analyzed from the two aspects of the battery component bracket and the lamp pole, and the analysis is relatively comprehensive; the surface treatment adopts the most advanced technology and process at present; the overall structure of the street lamp is simple and beautiful; and the actual operation proves that the matching between each link is good.

At present, the initial investment of solar LED lighting is still a major problem that bothers us. However, the light efficiency of solar cells is gradually improving, while the price will gradually decrease. Similarly, the light efficiency of LEDs in the market is rapidly increasing, while the price is decreasing. Compared with the renewable, clean and pollution-free solar energy and the environmental protection and energy saving of LEDs, conventional fossil energy is becoming increasingly scarce, and its use will cause increasingly serious pollution to the environment. Therefore, as a burgeoning outdoor lighting, solar LED lighting will show us infinite vitality and broad prospects.