With the development of economy and the progress of society, people have made higher and higher demands on energy. Finding new energy has become an urgent issue facing humanity. Solar energy is considered to be the most important energy source in the 21st century because solar power has the advantages of cleanliness, safety, extensiveness, and adequacy of resources that cannot be matched by thermal power, hydropower, and nuclear power. At present, solar energy application technology has made great breakthroughs, and has been more maturely applied to architectural corridor lighting, urban lighting lighting, solar hot water supply and heating systems. In particular, the development of solar photovoltaic technology has brought a broader perspective to the application of solar energy in lighting.
1 Solar PV Technology
Solar photovoltaic technology is a technology that uses solar cells to convert solar energy directly into electrical energy. Solar photovoltaic systems mainly include: solar cell modules, batteries, controllers, inverters, lighting loads and so on. When the lighting load is DC, there is no inverter.
1.1 Solar Cell
Solar cell modules are solid-state devices that utilize the electronic properties of semiconductor materials to achieve PV switching. The solar cell modules used in solar lighting fixtures are made up of several solar cells in parallel. Because of the limitations of current technology and materials, the power generation of a single cell is very limited. A common single cell is a silicon crystal diode. When sunlight strikes a PN junction made of P-type and N-type homogenous semiconductor materials of different conductivity types, under certain conditions, solar radiation is irradiated by the semiconductor material. Absorption forms a built-in electrostatic field. Theoretically, at this time, if the electrodes are drawn on both sides of the built-in electric field and an appropriate load is connected, an electric current will be formed. In recent years, the development of amorphous silicon solar cells has made even greater progress. Because of its advantages such as lower production cost, simple process, and saving raw materials, it will occupy an important position in the future photovoltaic technology. The output power of solar cells is random. At different times and at different locations, the output power of the same solar cell is different. The peak power Pm of a solar cell is determined by the local average solar radiation intensity and the end-use electrical load.
1.2 Battery
Since the input energy of the solar photovoltaic power generation system is extremely unstable, a battery system generally needs to be configured to work. Direct current generated by solar cells enters the storage battery and reaches a certain threshold before it can supply lighting loads. The characteristics of the battery directly affect the system's operating efficiency, reliability, and price. The selection of the battery capacity generally follows the following principles: First, the energy of the solar cell modules in the daytime should be stored as much as possible under the premise that the night lighting can be met, and at the same time, the electric energy required for the lighting of the predetermined continuous rainy and cloudy nights should be stored.
1.3 Controller
The controller's role is to make solar cells and batteries work safely and reliably to maximize efficiency and extend battery life. The controller limits the charge and discharge conditions to prevent battery reverse charging, overcharging, and overdischarging. In addition, it should also have circuit short-circuit protection, reverse connection protection, lightning protection and temperature compensation. Since the output energy of the solar battery is extremely unstable, the quality of the charge and discharge control circuit is crucial to the design of the solar lamp.
1.4 DC-AC Converter
The main function of the inverter is to convert the DC power of the battery into AC power. The inverter circuit is used to obtain the sinusoidal AC power supply system end users who match the lighting load rated frequency and rated voltage through modulation, filtering and boosting. The inverter should also have the functions of circuit short-circuit protection, under-voltage protection, over-current protection, reverse polarity protection and lightning protection.
2. Solar Lighting Solutions
The application of solar photovoltaic technology not only has a very important position in remote areas and areas of temporary power shortage, but also has been rapidly popularized in other areas. It has been used in various industries such as transportation, construction, agriculture and forestry. Especially in lighting projects, it is even more colorful.
2.1 City Lighting Lighting
At present, the application of solar photovoltaic technology in urban lighting lighting has started and is gradually popularized with the rapid development momentum. Signs, warning signs, lawn lamps, street lamps, etc. in schools, parks, residential communities, villas, etc., can use solar photovoltaic lighting technology, making public lighting more convenient, safe, environmentally friendly, and energy-efficient. The working principle of solar lighting lighting is: the solar panel as a power generation system, so that the battery power supply through the high-power diodes and control system to charge the battery, when the battery power reaches a certain level, the control system built-in automatic protection system action, The battery board automatically cuts off the power and performs automatic protection. At night, the solar panels also played a role in light control and gave instructions to the control system. At this time, the control system automatically turned on and output voltage, so that all kinds of lamps reached the designed lighting effect. Adjust the lighting time required.
Solar lighting lighting technology has a one-time investment, no long-term operating costs, easy installation, maintenance-free, long service life, etc. It will not damage the original vegetation, the environment, but also reduce the cost, save energy, can be described as "There is more to do at one stroke."
2.1 Building corridor lighting
Solar corridor lights are powered by solar panels. The whole building adopts overall layout, split installation and centralized power supply. The solar energy is installed on the roof or roof and is sent to each walkway and stairway with a special wire (reserve). The system uses sound and light sensing and delay control. During daytime system charging, the device automatically switches on at night, and when it detects a walking message, it automatically activates the lighting device and turns off itself after a delay of 3 to 5 minutes. When sudden accidents such as fires or earthquakes cut off power supply or regional power outages in the building, they can continue to supply power for 3 to 5 hours. They can be used as emergency lights and reflect the humanized design philosophy while reducing costs. Such products can also be used in the residential building number plate, unit door number, etc., to provide convenience for the returning guests and visiting guests.
2.3 "Photovoltaic-architecture lighting integration" technology.
At present, solar modules and building components have been successfully integrated, such as solar roofs (tops), walls, doors and windows, to achieve the "photovoltaic-building lighting integration (BIPV)." The working principle of this system is that: a solar panel composed of a plurality of monocrystalline silicon solar photovoltaic cells emits a direct current after the irradiation of sunlight and generates a photoelectric effect, and then the direct current is converted into a general electrical apparatus by a power converter in the system. The required AC power, which can be used in lighting, air conditioning and other systems via the power distribution system, as well as storage batteries for storage of electricity, can still provide emergency power needs for disaster prevention. The shape, color, architectural style of the PV components of the building's walls and roofs are combined with the buildings and integrated with the surrounding natural environment in order to achieve perfect coordination. A domestic aluminum curtain wall manufacturing company successfully developed a "solar house" that integrates power generation, energy saving, environmental protection, and value-added into a room. It successfully integrated photovoltaic technology with building technology, known as the solar building system (SPBS). Experts argue. This will effectively promote the industrialization and marketization of solar building energy efficiency.
3 Solar Lighting
Solar lighting equipment mainly consists of lighting fixtures, light sources and control systems.
Solar lighting fixtures mainly include solar lawn lights, garden lights, landscape lights and pole lights. These luminaires use sunlight as their energy source and are charged during the day and used at night without the need for complex and expensive pipeline laying, and the layout of the luminaire can be arbitrarily adjusted. The light source generally uses LED or DC energy-saving lamps, which has a long service life and is a cold light source, which is harmless to the growth of plants. Solar lighting lighting is an automatic control system. It can work automatically by setting the working mode of the system. The control mode is generally divided into a light control mode and a timing control mode, and generally uses a light control or light control and timing combination work mode. When the light intensity is lower than the set value, the controller startup lamp lights, and timing starts. When the time is up to the set time, it stops working. The charging and switching process can be controlled by a microcomputer intelligently, automatically switching, without manual operation, stable and reliable work, saving electricity costs, and maintenance-free.
Among them, the solar landscape lamp design mostly uses the combination of metal and engineering plastics die-casting molding, the lamp body can present a variety of shapes such as round, square, geometric patterns, and thousands of styles, different styles, or luxurious and elegant, or simple and neat. The body color is white, red, green, blue, purple, yellow, etc. After the darkness, the system automatically activates the lighting device. At a glance, the lamp body emits uniform and soft light, several colors leaps and fades, and the night of the entire city pulsates in the moment. The solar pole lamp is generally 8 to 13 meters high, lighting power 50W ~ 130W, effective lighting area of ​​up to several hundred square. As night falls, neon flashes, brilliance, and extravagance.
4 Solar Lighting Cost Analysis
In recent years, the production capacity of solar cells in China has soared. The price of its products has also dropped from 80 yuan/watt in the early period of the “July 5th†to the current 40 yuan/watt. The price bottleneck that promotes the use of solar photovoltaic application products has been basically solved, and the promotion of its products is no longer constrained by the high price of solar photovoltaic products, which is expected to become inaccessible and rapidly popularized. It is expected that by the 20th and 30th centuries of this century, the cost of solar power could be reduced to the level of conventional electricity prices.
The use of solar lighting project will save a lot of money every year. It will not only illuminate the city but also ecologically develop the city and make full use of energy. It is currently the most reasonable development direction in the world.
Take the solar stair walkway light of a 20-story high-rise apartment as an example: The one-time cost is about 10 yuan per square meter, and the service life is about 15 years or more; Compared with the emergency light with its own battery, the one-time cost is almost the same. Solar lighting has a longer life and it also saves electricity bills.
Take the solar garden lamp as an example: every 3,000 to 4,000 yuan is about twice as expensive as a regular garden light, but if you count the investment in electrical pipelines and distribution facilities plus 3 to 5 years of electricity and daily maintenance, The cost is basically the same.
5 Problems with solar lighting
5.1 Efficiency of Solar Photovoltaic System
The total efficiency of a solar photovoltaic system consists of the PV conversion rate, controller efficiency, battery efficiency, inverter efficiency, and load efficiency of the battery module. At present, the conversion rate of solar cells is only about 17%, and the efficiency of controllers, batteries, and inverters is much higher than this. For example, the efficiency of inverters has reached more than 95%. Therefore, improving the conversion rate of battery modules and reducing the unit power cost is the key and difficult point in the industrialization of solar power generation.
5.2 Solar Cell Capacity
At present solar cells are still difficult to use on main road lighting. Highway main road lighting has higher illumination requirements, and in terms of current solar cell conversion efficiency and price, it is still unable to meet this requirement. However, in the near future, with the improvement of the technological level, the application of solar lighting on the main highway will be popularized.
5. 3 Solar Energy Storage Components
The service life of a solar battery is more than 25 years, and the service life of an ordinary battery is 2 to 3 years. Therefore, the battery is the weakest link in the solar power system. The energy storage capacitor can solve this problem to some 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 energy storage components that are most promising for solar cells.
5. 4 Quality of Solar Products
In recent years, solar photovoltaic technology has developed rapidly and product manufacturers are springing up. However, some products do not form a series, quality is uneven, and there are many defects in the selection of light sources and circuit design, reducing the economical and reliable products. At the same time, the country lacks corresponding product quality standards and inspection systems, which will affect the industrialization of solar photovoltaic technology.
6 Conclusion
The development and utilization of solar energy is a far-reaching and near-effective business. Promoting the application of solar photovoltaic technology in lighting is a new topic. With the deepening of solar energy industrialization process and technology development, the efficiency and cost-effectiveness of solar photovoltaic technology will be rapidly increased. It will be widely used in various fields and will also greatly promote the rapid development of China's "green lighting project."
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