At present, the electricity consumed by lighting accounts for about 20% of the entire electricity consumption. Reducing the electricity consumption for lighting is an important way to save energy. In order to achieve this goal, the industry has researched and developed a variety of energy-saving lighting appliances, and achieved certain results. However, the requirements for “green lighting” are still far away, and it is imperative to develop and apply new types of light sources that are more efficient, reliable, safe, and durable.
As an emerging green energy, solar energy has been quickly promoted and applied with its unparalleled advantages. As the fourth-generation new light source LED, it has been effectively used in urban lighting and beautification, road lighting, courtyard lighting, indoor lighting and other lighting applications in various fields. Solar LED lighting systems, especially in remote areas without electricity, solar LED lighting systems have a wide range of application prospects.
With economic development, China’s lighting power consumption will be greatly increased, and the research and application of green energy-saving lighting will receive more and more attention.
As a cold light source product, solar LED lighting system has the characteristics of high cost performance, green environmental protection, safety and reliability, stable quality, long service life and simple installation and maintenance. It can be widely used in green space lighting, highway lighting, advertising light box lighting, urban modeling landscape lighting and home lighting systems, but the high one-time investment of solar LED lighting system is the bottleneck of its development.
In the 1990s, semiconductor green lighting has entered a period of real rapid development. A large number of various lighting fixtures combined with solar cells and LEDs have been widely used. The research fields of semiconductor green lighting systems include:
(1) Research on micro-power controllers and high-efficiency LED devices in solar LED lighting systems.
(2) Research on high-efficiency and long-life energy storage technology in solar LED lighting systems.
(3) Research on high-efficiency LED lighting fixtures.
(4) Research on the optimal matching between solar cells and LEDs.
In addition, a dedicated semiconductor lighting control chip was developed, and a module was designed on this basis, as shown in Figure 1, it has solar cells on the front and special semiconductor lighting control chips and LEDs in “soft packaging” on the back. It is particularly suitable for the field of urban landscape lighting, and it is also suitable for road lighting.
At the 15th International Photovoltaic Science and Engineering Conference, Sharp exhibited a solar cell glass curtain wall with LEDs installed on the back of their design. This new type of glass curtain wall composed of solar cells and LEDs is shown in Figure 2.
At present, people’s understanding of semiconductor green lighting is the narrow semiconductor green lighting that stays on LED lighting. Since solar cells are a new semiconductor energy source with great development potential, there is every reason to look at semiconductor green lighting from the system: It should be a semiconductor power generation, a semiconductor control circuit and semiconductor LED light source composed of a pollution-free, the most ideal lighting system for human beings, it can also be called semiconductor green lighting in a broad sense.
The solar cell and the LED need to be connected with a relatively complicated, even very complicated control circuit, and the control circuit is completely completed by semiconductor devices, that is, by countless PN junctions. In the independent semiconductor wall green lighting system, the battery needs to be charged and discharged. In order to meet the low voltage and constant current operating characteristics of the LED, it is also necessary to perform high-efficiency voltage and current conversion and many controls such as automatic switching on the power supply. Therefore, there should be countless PN junctions between the two PN junctions of solar cells and LEDs, which form a real semiconductor green lighting.
Semiconductor green lighting is not only the task of LED R&D and production departments. It should be the common task of silicon materials, battery manufacturing, solar cell module manufacturing, integrated circuit design and manufacturing, semiconductor power device manufacturing, and LED R&D and production departments. Especially the design of application-specific integrated circuits in the system is very important and urgent. The use of universal standard integrated circuits to manufacture semiconductor green lighting fixtures cannot meet the needs of the market in terms of energy saving and price.
As far as solar energy technology is concerned, lighting application is not its main application field, nor is it the field that best reflects its application advantages, but in terms of its manifestation as an energy source, lighting is the most intuitive and easy to be recognized and accepted by the public. However, at the current level, the high cost and low efficiency of solar energy technology as an energy source cannot be avoided. Especially in single lighting applications, if LED technology is not used, solar lighting systems are designed according to conventional methods, often facing its conversion. The electric energy is not enough to supply the embarrassment of the power consumption of the lamps. In this sense, LED has become the first choice for solar lighting applications due to its advantages of low energy consumption under the same visual effect and DC inverter-free during work. The current problems of solar LED lighting systems include:
(1) The efficiency of the solar photovoltaic system. The total efficiency of a solar photovoltaic system is composed of the conversion rate of the battery components, the efficiency of the controller, the efficiency of the battery, and the efficiency of the load. At present, the conversion rate of solar cells is only about 17%, and the efficiency of controllers and storage batteries are much higher than that of solar cells. Therefore, improving the conversion rate of solar cell modules and reducing the unit power cost are the key and difficult points of solar power industrialization.
(2) The capacity of solar cells. At present, it is difficult to use solar-powered LED lighting fixtures for main road lighting. The lighting of main roads on highways has higher illuminance requirements. In terms of the current conversion efficiency and price of solar cells, this requirement cannot be met. However, in the near future, with the improvement of technology, the application of solar LED lighting on the main roads of highways will definitely become popular.
(3) Solar energy storage components. The service life of solar batteries is more than 25 years, and the service life of ordinary batteries is 2 to 3 years, so batteries are the weakest link in solar LED lighting systems. Energy storage capacitors can solve this problem to a certain extent. The service life of the energy storage capacitor can reach more than 10 years, and the control circuit is simple, but the expensive price limits its application. At present, it is only applied to some traffic lights and decorative lights. With the development of technology and economy, it will be one of the most promising ideal energy storage components for solar LED lighting systems.
(4) The quality of solar products. In recent years, solar photovoltaic technology has developed rapidly. However, some products have not formed a series, and the quality is uneven, and there are even many defects in the selection of light sources and circuit design, which reduces the economy and reliability of the products. At the same time, the country lacks corresponding product quality standards and testing systems, which affects the industrialization of solar photovoltaic technology.
(5) As far as LED technology is concerned, entering the general lighting market is its ultimate goal. Among them, due to product performance characteristics, street lamp applications are its most important breakthrough.