In today's world energy shortage and increasingly serious environmental pollution, the full development and utilization of solar energy is a sustainable energy strategy decision for governments around the world. Solar street lights are not required to be managed and controlled by special personnel. Installation of one-time investment does not require future electricity bills. It is not necessary to set up transmission lines or trenches to lay cables. It can be easily installed in squares, campuses, parks, streets, etc. Pay attention to it.
The solar street lighting system usually consists of a solar cell module, a battery, a light source, and a controller (the AC source also requires an inverter). This article from: 1 light source selection; 2 control circuit; 3 solar panel optimal tilt angle determination; 4 solar cell components and battery capacity determination and other aspects of the design of solar street lighting system operating in Zhuhai.
Unlike ordinary street lamps, solar street lamps use solar cells as the only power source. Because the cost of solar cell modules is still relatively high, in order to reduce system cost, efficient light sources must be used. LED is a kind of semiconductor light-emitting device capable of converting electric energy into visible light. In recent years, LED technology has made a key breakthrough, and its performance price ratio has also been greatly improved. Compared with the traditional street light source, the LED light source has high light efficiency. Close to twice the incandescent lamp, the long life can reach more than 105h; the traditional light source consumes a lot of power, and most of them work under high voltage. The use of the boost inverter reduces the energy utilization, and the LED uses low-voltage DC power supply. Safety and low cost control of the light source make it possible to adjust the brightness and darkness and switch frequently.
Solar streetlight systems are generally small photovoltaic systems. The World Bank's standard is that small-scale photovoltaic system controllers consume less than 1% of the rated operating current. Therefore, the design of the controller circuit and the choice of low-power devices are very important. The solar street lamp adopts a voltage comparator composed of an integrated operational amplifier as a control circuit. This circuit is completely composed of a hardware control system, which is simple and reliable, easy to maintain, low in cost, and extremely low in power consumption of the circuit itself. A well-matched circuit. The key of this kind of circuit is to design a better voltage difference for the charge and discharge characteristics of the battery. At the same time, the selection of the device should be reliable. Together with the charge and discharge state indicating circuit formed by the LED, it becomes a practical function control. The circuit has anti-battery over-discharge and over-charge functions. The system adopts a direct-coupled charge-discharge controller circuit. According to the matching characteristics of the LED and the battery, the power can be adaptive. In the few months when the solar radiation is insufficient, the battery is discharged due to the low state of charge of the battery. The terminal voltage is also low, so that the load operating current is small, the power is small, and the system can work for a longer period of time. On the other hand, when the solar radiation is sufficient, the load operating current is large, the power is large, and the light is brighter.
Determine the optimal tilt angle of the solar panel
In an independent photovoltaic system design, the solar cell assembly plane is generally oriented toward the equator with a certain angle of inclination relative to the ground plane. Since the amount of solar radiation varies with seasons and climate, the inclination angle is different, and the solar radiation received in each month varies greatly, and since the battery is limited by its rated capacity when charging, the discharge is limited by the depth of discharge, so In the optimization design of solar street lamps, the optimal tilt angle should be determined according to the load situation, local climate conditions and geographical conditions, so that the solar radiation on the square plane should satisfy the continuity, uniformity and maximum requirements, and reduce the system. cost.
Load situation
Solar street light products mainly have two working modes of timing and light control, which are actually balanced load mode and seasonal load mode T. Timing control: no external influence, time switch light, there is a problem that the black light is not bright or the day light is still bright. The light-controlled solar street light automatically turns on when the outdoor light is dark to a certain extent (200 lx), when it is dawn The function of automatically turning off the light is that the light source can be automatically controlled according to the lighting condition. There is no case where the black light source is working and the black is not working, and it can work normally all year round. The working time of the light control method is related to the local latitude and the sun declination of the day. Formula by time angle of sunrise and sunset:
COs= COS L- tan ~tan8o ] (1),
J6-latitude; a declination, the declination of the day is the noon at the sun, the angle between the light and the equatorial plane.
Under normal circumstances, 0.5 h before sunrise and 0.5 h behind the mouth, although there is no sunshine, but there is still light in the sky, which is not necessary to turn on the lighting, so the working time of the solar-controlled solar street lamp is reduced.
For less than 1 h, you can use the following formula to calculate the working time of the street lamp:
T= 23—2/15cos one [one tan~tan8] (2)
Calculated by formula (2), the annual working time change of light-controlled solar street lamps installed in Zhuhai is shown in Figure 1. It can be seen from the figure that the longest working time of light-controlled solar street lamps is 12.35 h in the winter solstice and the shortest in summer solstice. j second time 9.65 h; due to the relatively low latitude of Zhuhai area, the annual working time of light-controlled solar street lights is not very large, so although the light-controlled solar street lights are seasonal unbalanced loads, the load changes are not very large. The load condition is not a major factor affecting the optimum tilt angle of the solar module. Taking into account the reliability of the control switch lamp and the cost of the controller, the solar street light designed in Zhuhai is operated in a light control mode.
Climate situation
Zhuhai City is located in the south of the Tropic of Cancer. It belongs to the south subtropical maritime monsoon climate with sufficient sunshine. The total annual solar radiation is 4 651.6 MJ/n~, which is one of the regions with abundant solar energy resources in Guangdong Province. It can be seen from Figure 2 that the least amount of total radiation in the Zhuhai area during the year is spring, with more rainy weather and poor atmospheric transparency. The towel and low clouds are often covered with sky, and the amount of time is scattered.
The proportion of total irradiation is very high. It can be seen from Table 2 that the proportion of scattered radiation in February is 65.6% of the highest value in the whole year; the summer is mainly sunny and hot, sunny, and the sun is irradiated on the horizontal surface.
The degree is the largest in the whole year, and the proportion of direct irradiation in the solar radiation is very high; the autumn in Zhuhai is high in the autumn, and the sky is clear, although the solar elevation is gradually decreasing, the solar radiation is still relatively high; In the sunny days, there are many but many winters, and the rainfall is scarce.
Inclined surface solar irradiance calculation
The solar radiation calculation on the inclined plane is generally based on the meteorological data of the past 10 to 20 years. Based on the provided solar radiation data of the horizontal plane, the model of sky scattering radiation anisotropy proposed by Hay_I can be used to calculate the equator. The amount of solar radiation received by the square faces of different dip angles.
Its expression is:
HT: H R8+Ho I_R H }H +0.s , ~HB|Ho)
(1+cosf1)J+0.5pH (1 one cosp) (3)
R : cos0 /cos0
Angle of incidence: =COS [cos0 cosfl+sin0 sinflcos
(y a y JJ
Zenith angle: =c0s [sinasin~+c0s c0s c0s∞][3
Solar azimuth: ys = d * dy . +
F_l 1* *180. _3
Hot n [ ={ . }'
Fl ≯ (≯一 01 fl ∞ 01
I-l other 'I-l otherã€'
=ar~cos(tan3/tan~) Lu is the slope angle, f0 is the surface reflectivity of the object, is the incident angle, 臼 is the solar zenith angle; a is the solar elevation angle;), is the surface azimuth, y is The azimuth of the sun. Through the calculation of the above Hay model, the monthly average solar radiation amount variation of the different inclination planes of FIG. 3 is obtained. It can be seen from Fig. 3 that during the period from February to April, the solar irradiance is the lowest during the dip plane, and the solar irradiance obtained by several dip planes is not much different during this period. The reason for the analysis is mainly due to 2-4. The month is the rainy season in Zhuhai. The weather is cloudy and rainy. The amount of scattered radiation is very high in the total amount of radiation. It can be seen from Table 2 that the proportion of scattered radiation in these 3 months is above 55%. Since changing the dip angle has a large effect on the direct radiation of the solar cell module, but the effect on the scattering radiation is not large, the difference in solar radiation received by the plane of different inclination angles of 2-4 in 3 months is not very large; In the summer of 5-8 months, to 0. The plane receives the largest amount of solar radiation, 15. And 22. The sun irradiance received by the inclined plane is very close, however 40. Compared with the other three kinds of dip angles, the amount of solar radiation received by the plane is much lower than that of the other three kinds of dip angles. In the autumn of Zhuhai, the autumn weather is high and the air is clear, and the sun's elevation angle is gradually reduced. The solar radiation is still relatively high, 15°. The solar radiation doses obtained by 22° and 40° tilt angle planes are very close, and 0 after September. The amount of solar radiation received by the plane is rapidly reduced, and the decline is very large. In winter, the number of sunny days is mostly, especially in the early winter, the rainfall is scarce. In the winter of 1 and 12 months, the elevation angle is the lowest period of the year, as seen from Figure 3 On the inclined surface of the angle, the amount of solar radiation varies greatly. At 40o, the maximum solar radiation can be obtained, and the solar radiation on the horizontal surface is seriously reduced. At the same time, the working time of the solar control system before and after the winter solstice is the whole year. The longest, therefore the angle of inclination should be properly taken care of the solar radiation in winter.
By analyzing the monthly average solar radiation variation of different dip planes in Figure 3, combined with our load situation, in the design of solar street lighting system, we must first consider the system in February-April low solar radiation.
According to the normal working demand of the illuminance situation, the light-controlled solar street lamps used in Zhuhai area are seasonal loads with large power consumption in winter, but the load changes are not very large, and the load situation is not a shadow.