1、System introduction
1.1 Introduction to the basic composition of the system
The system consists of solar cell module part (including bracket), LED light head, control box (with controller, battery) and light pole parts; solar panel luminous efficiency of 127Wp/m2, high efficiency, very favorable to the system’s wind-resistant design; light head part to 1W white LED large particles or white LED small particles integrated in the printed circuit board arranged as a certain spacing of the Dot matrix as a plane light source.
The control box is made of stainless steel, which is beautiful and durable; the maintenance-free lead-acid battery and charge/discharge controller are placed inside the control box. The system uses valve-regulated sealed lead-acid battery, which is also called “maintenance-free battery” because of its low maintenance, which is conducive to the reduction of system maintenance costs; the charge/discharge controller is designed to take into account both functional (with light control, time control, overcharge protection, over discharge protection and reverse connection protection, etc.) and cost control to achieve high cost performance. The design of the charge/discharge controller takes into account the full functionality (with light control, time control, overcharge protection, discharge protection and reverse connection protection, etc.) and cost control to achieve high cost performance.
1.2 Working Principle Introduction
The working principle of the system is simple, using the photovoltaic effect of solar cells made of solar panels during the day to receive solar radiation and converted into electrical energy output, after the charge and discharge controller stored in the battery, at night when the illumination gradually reduced to about 10lux, solar panels open circuit voltage of about 4.5V, the charge and discharge controller detects this voltage value after the action, the battery to the light head discharge. After the battery is discharged for 8.5 hours, the charge/discharge controller will act and the battery discharge will be finished. The main role of the charge and discharge controller is to protect the battery.
2、System design idea
LED solar street light design and general solar lighting compared to the same basic principles, but the need to consider more links. The following will be taken as an example of this solar LED high-power street light of Hong Kong Zenith Group Limited, in several aspects to do analysis.
2.1 Solar cell module selection
Design requirements: Guangzhou area, load input voltage 24V power consumption 34.5W, daily working hours 8.5h, to ensure the number of consecutive cloudy days 7 days.
(1) The average annual radiation in Guangzhou area in the past 20 years is 107.7Kcal/cm2, and the peak sunshine hours in Guangzhou area is about 3.424h by simple calculation.
(2) The daily power consumption of the load = = 12.2AH
(3) The total charging current of the solar module required = 1.05 × 12.2 × ÷ (3.424 × 0.85) = 5.9A
Here, the design minimum number of days between two consecutive cloudy days is 20 days, 1.05 is the solar module system integrated loss factor, and 0.85 is the battery charging efficiency.
(4) Minimum total power number of solar modules = 17.2 x 5.9 = 102W
The selection of a standard battery module with a peak output power of 110Wp and a single 55Wp should ensure the normal operation of the street light system under most circumstances in a year.
2.2 Battery Selection
Battery design capacity calculation is simpler compared to the peak wattage of solar modules.
According to the above calculation, we know that the daily power consumption of the load is 12.2AH. In the case of a full battery, it can work continuously for 7 rainy days, plus the first night’s work, the battery capacity.
12.2 × (7 + 1) = 97.6 (AH), the choice of two 12V100AH battery will be able to meet the requirements.
2.3 Solar cell module bracket
2.3.1 Tilt angle design
In order to let the solar module receive as much solar radiation as possible in a year, we have to choose an optimal tilt angle for the solar module.
The discussion on the best tilt angle of solar cell modules has appeared in a number of academic publications in recent years. This street light use area is Guangzhou area, according to this design reference in the relevant literature, selected solar cell module bracket inclination angle of 16o.
2.3.2 Wind-resistant design
In the solar street light system, a structural issue that needs to be paid great attention is the wind resistance design. The wind resistance design is mainly divided into two blocks, one is the wind resistance design of the battery module bracket, and the other is the wind resistance design of the lamp pole. The following is an analysis of the above two blocks respectively.
(1) Wind resistance design of solar cell module brackets
According to the technical parameters of the module manufacturer, the solar module can withstand a wind pressure of 2700 Pa. If the wind resistance factor is selected as 27m/s (equivalent to a ten-step typhoon), according to non-viscous fluid mechanics, the wind pressure on the module is only 365 Pa. Therefore, the module itself can fully withstand a wind speed of 27m/s without damage. Therefore, the key thing to consider in the design is the connection between the battery module holder and the light pole.
In the design of this set of street light system, the connection between the battery module bracket and the pole is designed to be fixed with a bolted rod.
(2) Wind resistance design of the street light pole
The parameters of the street light are as follows.
Battery plate inclination angle A = 16o Light pole height = 5m
The width of the weld seam at the bottom of the lamp pole is selected as δ = 4mm The outer diameter at the bottom of the lamp pole = 168mm
As shown in Figure 3, the weld seam is located on the damaged surface of the pole. The distance from the calculation point P of the resisting moment W to the line of action of the battery load F on the lamp pole is PQ = × Sin16o = 1545mm = 1.545m. Therefore, the moment of the wind load on the damaged 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-head 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 the mathematical derivation, the resistance moment W = π × (3r2δ + 3rδ2 + δ3) of the circular breaking surface.
In the above equation, r is the inner diameter of the ring and δ is the width of the ring.
The moment of resistance of the breaking surface W = π× (3r2δ + 3rδ2 + δ3)
= π × (3 × 842 × 4 + 3 × 84 × 42 + 43) = 88768 mm3
= 88.768×10-6 m3
Stress caused by the moment of wind load acting on the damage surface = M/W
= 1466/(88.768×10-6) = 16.5×106pa = 16.5 Mpa＜＜215Mpa
Where, 215 Mpa is the bending strength of Q235 steel.
Therefore, the width of the weld selected for the design meets the requirements, and as long as the welding quality can be guaranteed, the wind resistance of the lamp post is not a problem.
2.4 Controller
The main role of the solar charge and discharge controller is to protect the battery. The basic function must have overcharge protection, over discharge protection, light control, time control and anti-reverse connection, etc..
Battery anti overcharge, over discharge protection voltage general parameters such as Table 1, when the battery voltage reaches a set value to change the state of the circuit.
In the selection of devices, there are currently using a single-chip computer, there are also comparators, more programs, each with its own characteristics and advantages, should be selected according to the needs of the customer base characteristics of the corresponding program, not detailed here.
2.5 Surface treatment
The series of products adopt new technology of electrostatic coating, mainly FP professional building materials coating, which can meet the customer’s requirements of product surface color and environmental coordination, while the products are highly self-cleaning, corrosion resistant, aging resistant and suitable for any climatic environment. The processing process is designed to be painted on the basis of hot dip zinc, which makes the product performance greatly improve and meet the most strict requirements of AAMA2605.2005, and all other indicators have reached or exceeded the relevant requirements of GB.
3、Conclusion
The overall design basically takes into account all aspects; the peak wattage selection design of PV module and battery capacity selection design adopt the most common design method, and the design idea is relatively scientific; the wind resistance design is analyzed from both battery module bracket and lamp pole, and the analysis is relatively comprehensive; the surface treatment adopts the most advanced technology; the overall structure of the street light is simple and beautiful; the actual operation proves that the links The matching between them is good.
At present, the initial investment problem of solar LED lighting is still a major problem that plagues us. However, solar cell luminous efficiency is gradually improving, while the price will gradually reduce, similarly the market LED luminous efficiency is rapidly improving, while the price is reducing. Compared with the renewable, clean and non-polluting solar energy and LED’s environmental protection and energy saving, conventional fossil energy is becoming more and more nervous, and the use of the environment will cause increasingly serious pollution. Therefore, solar LED lighting as a kind of emerging outdoor lighting, show us will be endless vitality and broad prospects.