Solar LED street light composition and characteristics
Solar LED street lights use the photovoltaic effect principle of solar cells. During the day, solar cells absorb solar photon energy to generate electricity. The electricity is stored in the battery through the control of the photovoltaic controller. When the night falls or the light around the lamp is low, the electric energy supplies power to the light source through the control of the photovoltaic controller, and the controller cuts off the power source of the light source after a set time. Solar LED street light consists of the following parts: solar panel, solar LED street light controller, battery pack, light source, light pole and lamp housing.
1. Solar battery
The solar battery is the core part of the solar LED street light, and it is also the most valuable part of the solar LED street light. Its role is to convert the solar radiation capacity into electrical energy. There are three types of solar cells, such as monocrystalline silicon solar cells, polycrystalline silicon solar cells, and amorphous silicon solar cells. In eastern and western regions with good sunlight and good sunshine, it is better to use polycrystalline silicon solar cells, because the production process of polycrystalline silicon solar cells is relatively simple and the price is lower than monocrystalline silicon. In southern areas where there are many rainy days and the sun is relatively inadequate, it is better to use monocrystalline silicon solar cells, because the performance parameters of monocrystalline silicon solar cells are relatively stable.
For silicon solar cells, under standard conditions (spectral illuminance: 100W / m2, spectrum: AM1.5, temperature: 25 ° C), its open circuit voltage is 0.48 to 0.6V. By connecting and encapsulating a plurality of single solar cells, solar cells with different areas and different powers can be formed, and can also be collectively referred to as solar panels. Monolithic solar cells are generally unusable, and the actual application is solar cell modules.
At present, there are mainly two types of packaging methods for solar cells: lamination process and glue-drop process. Solar cells packaged with the laminate process can guarantee a working life of more than 25 years, and its process characteristics and service life are better than the glue-filled form. No matter which type of solar cell has the following five electrical parameters: short-circuit current Isc; peak current Im; open-circuit voltage Voc; peak voltage Vm; peak power Pm = Im × Vm.
Peak power of solar cells is the maximum power output by solar cells (modules) under standard conditions (ie STC: 101 standard defined by the European Commission, radiant intensity 1000W / m2, atmospheric quality AM1.5, battery temperature 25 ° C), unit peak Watts, or with the symbol Wp. The output power of a solar cell (module) depends on the solar irradiance, the solar spectral distribution, and the operating temperature of the solar cell (module). The output power of the same solar cell is different at different times and in different places.
Calculated by area, the output power of a solar cell per square meter is about 120W; as the conversion efficiency increases, its output power also increases accordingly. The selection of the output power of the solar cell module should be determined according to the light source power of the solar lamp, the use time and the local climate and geographical conditions.
During the use of a solar cell module, if a piece of solar cell is alone blocked by leaves and other obstructions for a long time, the blocked monolithic solar cell will be heated and damaged under strong sunlight, and even the entire solar cell module will be damaged. It is the so-called heat island effect. In order to prevent the heat island effect, the solar cell is generally placed obliquely so that the surface of the solar cell cannot be blocked.
Since China ’s north-south latitude spans a lot, the angle of installation of solar cell modules varies with the latitude of the installation area. In general, the installation inclination angle in the south of the Yangtze River is about 30 °; the installation inclination angle in the north of the Yangtze River is about 45 °; in the northeast, it should be about 50 °. The direction is south or west. The output power of a solar cell placed horizontally will be reduced by 15% to 20%.
2. Photovoltaic controller
No matter the size of solar lamps, a good performance charge and discharge controller is essential. In order to extend the service life of the battery, it must limit its charging and discharging conditions to prevent the battery from overcharging and deep charging. Where there is a large temperature difference, a qualified controller should also have a temperature compensation function. At the same time, the solar controller should also have street light control functions, with light control and time control functions, and it should have automatic load control at night, which is convenient for extending the working hours of solar LED street lights in rainy days.
For any solar lighting system, the quality of the charge and discharge control circuit will directly affect the success or failure of the system application. Because the energy input from a solar photovoltaic power generation system is extremely unstable, in a photovoltaic power generation system, the control of battery charging is more complicated than the control of battery charging with a commercial charger. A good-performance photovoltaic controller should have various protection functions such as controlling battery charge and discharge, temperature adjustment, maximum power tracking and overcharge protection, overdischarge protection, short circuit protection, reverse connection protection, as well as automatic switching and time adjustment functions to ensure the system operates reliably. At the same time, the photovoltaic controller also has the function of enabling the solar cell module to intelligently output the maximum power under different temperature and different solar irradiation conditions, so that the solar photovoltaic system has high efficiency.
3. Accumulator
Since the battery charging of the solar photovoltaic system is directly provided by the solar cell, the energy obtained is extremely unstable, so a battery with reasonable capacity and reliable performance must be configured to ensure the normal operation of the solar photovoltaic system. In solar photovoltaic lighting systems, maintenance-free lead-acid batteries are usually selected. The maintenance-free lead-acid battery adopts a fully sealed method, which has a high discharge rate and stable characteristics; no water needs to be added; simple installation, small footprint, and horizontal and vertical installation; the expected life is generally 5 to 7 years. The general principle for selecting the battery capacity is: first, it is sufficient to meet the night lighting requirements, and it can store the energy generated by the solar cell modules during the day as much as possible, and at the same time, it can also meet the power required for continuous night lighting on rainy days. The battery capacity is too small to meet the needs of night lighting, the battery capacity is too large, the battery is in a state of power loss for a long time, the battery life is shortened, and unnecessary investment is wasted.
A simple method can be used to determine the relationship between them, that is, 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 must exceed the working voltage of the battery by 20-30% to ensure the normal charging of the battery. The capacity of the battery must be more than 6 times higher than the daily consumption of the load. The basic requirements for the battery pack used by solar LED street lights are:
① Low self-discharge rate; ② Long service life; ③ Strong deep discharge capability; ④ High charging efficiency; ⑤ Less maintenance or maintenance-free; ⑥ Wide operating temperature range; ⑦ Low price.
4. LED light source
Because the working current of the LED is DC, and the working voltage is low. Solar cells convert light energy into DC electrical energy, and solar cell components can be combined in series and parallel to obtain the actual required voltage. These characteristics are exactly matched with LED. The combination of the two will obtain high energy utilization, high safety performance and reliability, and achieve energy-saving, environmental protection, safe and efficient lighting system, and realize a perfect combination.
The key to the perfect combination of solar photovoltaic power generation technology and LED lighting is that both are direct current, the voltage is low, and they can match each other. Therefore, the combination of the two does not need to convert the direct current generated by the solar cell into alternating current, thereby greatly improving the efficiency of the entire lighting system. At the same time, the use of batteries to store and release energy makes its advantages more obvious. With the in-depth study of related technologies, the luminous efficiency of LEDs is continuously improving. The advent of ultra-high-brightness LEDs will inevitably replace ordinary lighting electric light sources, and can save a lot of energy without pollution.
LED lamps have the advantages of long life, up to 1000000h, low operating voltage, no need for inverter, high light efficiency, etc. The domestic production is 50lm / W and the imported is 80lm / W. As technology advances, the performance of LEDs will further improve. LED lamp is a new type of lighting method that realizes the lighting requirements by lighting the LED module with DC low voltage. It has the characteristics of high brightness and good color rendering. In addition, because the input of LED street lights is low voltage DC, it can be connected with solar cells. LED as the light source of solar LED street lights will be the future development trend.