Analysis of the design of solar high power LED street light

In recent years, with the development of solar photovoltaic technology and LED lighting technology, solar LED street lamps have entered the field of urban lighting. LED is the abbreviation of Light Emitting Diode. LED as illumination source has DC low voltage drive compared with traditional illumination source; low power consumption; anti-vibration; long life; nanosecond response speed; large design space ;Environmental protection; continuous switching flash, easy to achieve 0-100% dimming function and other outstanding advantages, is considered a new generation of green lighting. Solar LED street lights use solar energy as an energy source. Each street lamp is independent, easy to install, no need to lay cables and wires, no need to exchange electric energy and electricity, DC power supply, light control timing control, safe and reliable, energy saving, economical, environmentally friendly, practical.

In this paper, for the purpose of practical application, the principle of solar cell power selection and the matching method of battery capacity are briefly introduced. The LEDs are analyzed and configured in terms of chip power selection, combination mode and driving mode, and designed to meet the road lighting use in Taiyuan. Solar LED street lights required.

Selection of solar panels and batteries

1, solar panel selection

At present, silicon-based solar cells are classified into three types: single crystal silicon solar cells, polycrystalline silicon solar cells, and amorphous silicon thin film solar cells. At present, the photoelectric conversion efficiency of monocrystalline silicon solar cells is about 15%, and the highest is 24%. Currently, all kinds of solar cells have the highest photoelectric conversion efficiency and the most mature technology. The service life is generally up to 15 years and up to 25 years. The photoelectric conversion efficiency of polycrystalline silicon solar cells is much lower than that of monocrystalline silicon solar cells. The photoelectric conversion efficiency is about 12%, and the service life of polycrystalline silicon solar cells is also shorter than that of monocrystalline silicon solar cells. The photoelectric conversion efficiency of amorphous silicon thin film solar cells is low. At present, the international advanced level is about 10%, and it is not stable enough. As time goes by, its conversion efficiency is attenuated, which directly affects its practical application. Therefore, solar cells are currently used in monocrystalline silicon solar cells.

According to the principle of solar radiation, the amount of radiation obtained on the solar array is related to many factors: local latitude, altitude, atmospheric pollution or transparency, changes in the four seasons of the year, changes in one day, reaching the ground. The ratio of the direct and scattered components of the solar radiation, the reflection coefficient of the ground surface, the operation mode of the solar cell array or the inclination of the fixed square matrix, and the cleanliness of the surface of the solar cell array. The charging and discharging efficiency of the solar lighting system is 0.75, the loss correction coefficient of the solar battery module group is 0.95, and the dust shielding and other loss correction coefficient is 0.90. After the query data and unit conversion and simplified processing, the formula for calculating the total solar cell consumption P(Wp) can be obtained[1]

Where, QL is the daily power consumption (Wh) of the load, HL is the annual average daily radiation amount of the horizontal plane (KJ/m2·d), Kop is the optimal radiation coefficient of the slope radiation, and A is the safety factor, generally taking A=1.1-1.3 .

Battery selection

Since the input energy of the solar photovoltaic power generation system is extremely unstable, it is generally necessary to configure the battery system to work. The selection of the battery capacity generally follows the following principles: First, the energy of the daytime solar battery module is stored as much as possible while meeting the night illumination. At the same time, it is also necessary to be able to store the electrical energy needed to meet the nighttime lighting of a continuous rainy day (seven days). If the battery capacity is too small, it can not meet the needs of night lighting. The battery capacity is too large. On the one hand, the battery is always in a deficient state, which affects the battery life and causes waste. At present, the valve-controlled sealed lead-acid battery is often used in conjunction with solar photovoltaic cells. Because of its low maintenance and reliable performance, it is also called "maintenance-free battery", which has the superiority that other batteries can't match.

The capacity of the battery should be determined according to the power of the solar panel and the power of the LED street lamp and the lighting time. The battery should be matched with the solar cell and the LED street lamp. A simple way to determine the relationship between them. The solar cell power must be more than 4 times higher than the load power for the system to work properly. The voltage of the solar cell should exceed 20~30% of the working voltage of the battery to ensure normal storage of the battery. The battery capacity must be more than 6 times higher than the daily load of the load.

The calculation of the capacity Bc of the battery can be calculated by the following formula:

Bc=(PL*10*D)/(Kb*V)

Where: PL - average daily power consumption

D—the number of rainy days

Kb—safety factor = 1.1-1.4 (including temperature correction factor To = 0 for 1 degree, -10 for 1.1, -10 for 1.2, and depth of discharge for cc = 0.75)

V—operating voltage

According to the above formula, the capacity of the battery can be estimated, and the charging efficiency of the battery depends on the charging method. For charging the battery, the method is usually to charge quickly in the initial and middle stages to restore the capacity of the battery. At the end of charging, a small current is used to supplement the battery for the loss of self-discharge. After the battery reaches the state, PWM (pulse width modulation) is adopted. Charging method to increase the conversion efficiency of solar energy and ensure the charging effect of the battery. During the initial discharge of the battery, the voltage drops rapidly; the mid-term voltage drops slowly and lasts for a long time; at the end of the discharge, the discharge voltage drops sharply, and the discharge stops immediately, otherwise the battery will be irreversibly damaged. In the charging and discharging process of the battery, in addition to setting a proper charging and discharging threshold, it is necessary to perform appropriate temperature compensation on the charging and discharging threshold and perform necessary overcharge and overdischarge protection. According to the system requirements and the verification of various indicators, 12V/100Ah valve-regulated sealed lead-acid batteries are selected.

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