Design ideas for solar street lights

Solar module conversion efficiency and production technology are constantly improving, and solar photovoltaic power generation application is becoming more widespread. In the lighting field, solar street lights have become the primary application mode of PV power generation systems and are becoming more and more recognized and accepted. We have analyzed the solar street light information of many companies and found that many people consider more partial in the design of a solar street light system, for example, the consideration of peak time, the choice of battery capacity and the understanding of continuous cloudy and rainy days.

This paper combines the actual experience in work and the design points of solar street lights for further discussion and analysis.

1 The basic structure and working principle of solar street light

1.1 Basic structure of solar street light

Solar street light is mainly composed of solar cell modules, components, brackets, light source, controller, battery, light pole, and other parts.

1.2 Working Principle of Solar Street Light

Solar street light uses the photovoltaic effect principle of solar cells. During the day, solar cells absorb solar photon energy to produce electricity, which is stored in the battery through the controller, and when night falls or the light level around the lamps is low, the battery supplies power to the light source through the controller until the set time and then cut off.

2 Data required for street light design

2.1 Find the longitude and latitude of the place of use by knowing where the solar street light is used.

Determine the tilt angle and azimuth of the solar cell module and calculate the solar standard peak sunshine time in the area by using the solar radiation database on different tilt surfaces.

2.2 The power (W) of the light source selected for the street light.

The size of the light source power directly affects the stability of the parameters of the whole system.

2.3 The working time (H) of the solar street light every night.

This is the core parameter that determines the size of the components in the solar street light system. By determining the working time, the daily power consumption of the load and the charging current of the solar cell module corresponding to it can be calculated initially.

2.4 The number of consecutive cloudy days (d) that the solar street light needs to maintain.

This parameter determines the size of the battery capacity and the solar cell module power required to restore the battery capacity after a cloudy day.

2.5 Determine the number of days between two consecutive cloudy days.

This determines the battery module power required to fill the battery after one consecutive cloudy day.

3 Solar street light system design ideas and key points

The basic principle of solar photovoltaic power generation system is the same, so the design idea of solar street light can also be based on the general solar power generation system. First, determine the power of the light source and the daily working hours to ensure a few cloudy days, and then calculate the capacity of the battery and the power of the solar cell module. But solar street lights have their own special characteristics and need to ensure the stability and reliability of the system work, so the design needs special attention.

3.1 Solar cell module

The voltage of the solar cell module will decrease as the temperature rises. Due to the high temperature, the voltage loss of the module is about 2V, while the voltage drop of the diode on the charging process controller is 0.7V, so the module with an operating voltage of 18V is selected. Due to the special nature of solar street lights, solar panels are generally installed on the poles. For street light poles, generally more than 5 meters, the center of gravity is higher, and most of the solar panels are suspended. In order to enhance the wind resistance of the whole set of equipment, we generally choose multiple solar panels to form the required component power.

3.2 Battery (group)

In the selection of the battery, one must consider the discharge rate of the battery capacity, the temperature of the battery capacity, the depth of discharge of the battery capacity, and several other aspects. So be sure to use a deep-cycle solar battery. When the battery is connected in parallel, it is necessary to consider the impact of the imbalance between the individual batteries; usually, the number of parallel groups should not exceed four groups.

3.3 Selection of light source

The selection of a light source for solar street lights is the most critical step. At present, for solar street lights, the dedicated light source is less. In order to reduce the loss of limited energy, the light source try to choose DC light source. LED, as a semiconductor light source, its development momentum is strong and is the most ideal light source for solar street lights. LED street light source is a multi-functional, environmentally friendly energy-saving street light source, suitable for use in a variety of lighting occasions. LED street light driver is a product developed specifically for the LED street light system, used to provide a stable power supply for LED lamps and lanterns. Using advanced electronic power technology, it is designed with two output modes: high-efficiency enhancement and super energy-saving pulse width modulation (PWM).

For time control, it can light up LED lamps in high-efficiency enhancement mode when needed (the first half of the night when it is dark and there are many people and cars) to provide good lighting working results and in other times (the second half of the night when there are few people and cars) in super energy-saving mode to save the battery’s power consumption. In addition, most of the solar street light project lighting brightness needs to meet the city road lighting standards.

3.4 Controller

The controller is a key component of the whole street light system, acting as a manager, and its most significant function is overall battery management. A suitable controller should set each key parameter point according to the characteristics of the storm, such as the battery overcharge point, over-discharge point, recovery connection point, SOC discharge control, etc. In the choice of street light controller, one especially needs to pay attention to the controller recovery connection point parameters because the battery has voltage self-recovery characteristics. When the battery is in the over-discharge state, the controller cuts off the load, and then the battery voltage recovery. If sometimes the controller parameters are not set properly, there may be flickering lamps and lanterns, which shorten the life of the battery and light source.

4 Conclusion

The solar street light design needs to be scientific and reasonable, in addition to the above points, but also needs to consider the overall structure of the street light, especially the calculation of the wind resistance of the street light and the overall aesthetics of the street light design combined with urban roads, In short, the solar street light performance of many factors, not to repeat, some people in the design of solar street light system often take the sunlight hours as the peak hours of solar energy, in fact, this is incorrect. The result of such a design will lead to the instability of the whole system. Only after mastering the detailed meteorological resources and conditions of use, combined with practical experience, can we optimize the system design to ensure that solar street lights can work properly.

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