The principle of solar LED lighting
The principle of solar LED lighting is shown in Figure 1. When light irradiates the surface of the solar cell, part of the photons are absorbed by the silicon material, and the energy of the photons is transferred to the silicon atoms, causing the electrons to undergo transitions, becoming free electrons that gather on both sides of the PN junction to form a potential difference. When the external circuit is turned on, under the action of this voltage, a current will flow through the external circuit to produce a certain output power. The essence of this process is the process of converting photon energy into electrical energy.
In the solar LED lighting system, the total efficiency η of the system is composed of the photoelectric conversion rate of solar cell components, the efficiency of the controller, the efficiency of the battery, the efficiency of the driver and the load, etc. At present, the photoelectric conversion rate of solar cells is only about 17%. Therefore, improving the photoelectric conversion rate of solar cell components and reducing the unit power cost of solar LED lighting systems are the key and difficult points of the industrialization of solar LED lighting. Since the advent of solar cells, crystalline silicon has maintained a dominant position as the main material. The current research on the conversion rate of silicon solar cells mainly revolves around increasing the energy-absorbing surface, such as double-sided cells; reducing reflection; using gettering technology and passivation technology to improve the conversion efficiency of silicon solar cells; ultra-thin cells, etc.
Features of solar LED lighting system
Compared with ordinary solar lighting systems, solar LED lighting systems have the following remarkable features:
(1) The luminous efficiency of LED is high and the brightness is high. The light source efficiency of LED has reached 100lm/W, and there is still a lot of room for development, the theoretical value can reach 250lm/W. The luminous efficiency of high-pressure sodium lamps increases with the increase of power. Therefore, the overall luminous efficiency of LED street lights is higher than that of high-pressure sodium lamps; the solar cell area and battery capacity can be reduced accordingly, or under the same solar cell area and battery capacity, the number of continuous rainy days can be extended.
(2) LED has long life and reliable product quality. The service life of the LED is more than 50,000h, which is basically synchronized with the use time of the solar battery, which greatly improves the overall performance of the solar lighting system. The general solar lighting lamps usually use electronic energy-saving lamps as the light source. The lamp life is 3000~5000h, and the light decay is obvious. Basically, it needs to be replaced once a year. The luminous decay of the LED light source is small, less than 3% in one year, and it can still meet the illumination requirements for road use after 10 years of use, while the high-pressure sodium lamp has a large decay, which has dropped by more than 30% in about a year. Therefore, the LED light source can be designed with lower power than the high-pressure sodium lamp.
(3) Solar LED street lights and LED garden lights adopt a new type of fully automatic solar lighting controller, which has the functions of light control, time control and adjustable luminous brightness. It starts to work at full power when it is dark, works at half power at midnight, and automatically shuts down after dawn. The half-power working period can be set according to user requirements, and the set period can be different every day. After setting, it will work automatically in a cycle of seven days. The use of traditional lighting fixtures to control the light can only be done by turning off some of the lights, causing dark areas in the road illuminance, causing safety hazards, and it has been banned by some countries in the world. The unique secondary optical design of the solar LED street light irradiates the light of the LED street light to the area that needs to be illuminated, further improving the light efficiency, in order to achieve the purpose of energy saving.
(4) Solar energy LED lawn light, LED underground lights and LED special controllers can achieve various dynamic effects such as colorful jump, gradual change, chase, water flow, expansion, compression, etc., and can also be combined and arranged into a certain dynamic pattern according to application requirements. It is widely used in garden squares, pedestrian streets, courtyards, parks, roads, gardens and other occasions.
(5) LED is a low-voltage working product, it can be used directly without inverting the voltage to AC220V. It not only improves the working efficiency of the solar LED lighting system (the inverter will generate 20% power consumption), and there is no hidden danger of power safety. LED is a low-voltage device. The voltage for driving a single LED is a safe voltage, so it is a safer lighting fixture than using high-voltage lighting fixtures, especially suitable for public place applications (such as: street lighting, factory and mine lighting, automotive lighting, civil lighting, etc.).
(6) LED as a point light source, if the design is reasonable, it can directly solve the secondary light distribution and light loss problems that traditional spherical light sources must rely on light reflection to solve. The uniformity of the light irradiation surface is controllable, and theoretically it can be completely uniform in the target area, which can also avoid the phenomenon of “lighting under the lamp” of traditional light sources and reduce light waste.
(7) The color temperature is optional. It is an important way to improve efficiency and reduce costs in applications in different occasions, and there is still a lot of room for technological progress. The light color rendering of solar LED street lights is much higher than that of high-pressure sodium lamps. The color rendering index of high-pressure sodium lamps is only about 23, while the color rendering index of LEDs is above 75. From a visual and psychological point of view, to achieve the same brightness, the average illuminance of the LED can be reduced by more than 20% compared with the high-pressure sodium lamp (refer to the British principle of lighting standards).
Read more: The color temperature of the light source
(8) LED light is unidirectional, without light diffusion, ensuring light efficiency; each unit LED has only a small volume, so it can be prepared into various shapes of devices, and is suitable for variable environments. Solar LED street lights have a large irradiation area: traditional high-pressure sodium lamps must rely on the height of the pole to achieve a sufficient irradiation area, and the LED street lamp itself can emit light at an angle of 140°, which can sprinkle effective light on the road. At the same time, the height of the lamp pole is saved. Generally, the lamp pole of 10m high pressure sodium lamp can reach the same irradiation area with only 8m with LED light source.
(9) The construction is quick and convenient. Each solar LED lighting system is an independent lighting unit, charging, discharging, and control are completed independently, without trenching, wiring, backfilling, instant installation and instant application.
(10) Low maintenance cost: Compared with traditional street lights, the maintenance cost of solar LED street lights is extremely low. After comparison, all input costs can be recovered in less than two years.