Solar power is a device that uses solar modules to convert solar energy directly into electrical energy. Solar cells are solid devices that use the electronic properties of semiconductor materials to achieve PV conversion. In a wide range of non-power network areas, the device can easily realize power supply for users and live. Some developed countries can also work with regional power grids. The grid is complementary. At present, from the perspective of civil use, foreign technology research is becoming more mature and industrialized is the "photovoltaic--building (lighting) integration" technology, while the domestic main research and production is suitable for small-scale solar power generation for home lighting in non-electric areas. system.
1 Principle of solar power generation
The solar power generation system mainly includes: a solar battery module (array), a controller, a battery, an inverter, and a user, that is, a lighting load. Among them, the solar cell module and the battery are power supply systems, the controller and the inverter are control protection systems, and the load is a system terminal.
1.1 Solar Power System
The solar cell and the battery constitute the power supply unit of the system, so the battery performance directly affects the operating characteristics of the system.
(1) Battery unit:
Due to technical and material reasons, the power generation of a single battery is very limited. A practical solar cell is a battery system in which a single battery is composed of a series and a parallel, which is called a battery assembly (array). A single cell is a silicon crystal diode that, under the conditions of a semiconductor material, is irradiated onto a PN junction of a homogeneous semiconductor material of two different conductivity types, P-type and N-type, under certain conditions. Solar radiation is absorbed by semiconductor materials, producing unbalanced carriers, electrons and holes, in the conduction and valence bands. The same as the PN junction barrier region, there is a strong built-in electrostatic field, so that the current density J, the short-circuit current Isc, and the open circuit voltage Uoc can be formed under illumination. If the electrodes are drawn on both sides of the built-in electric field and connected to the load, theoretically, the circuit formed by the PN junction, the connecting circuit and the load has a "photogenerated current" flowing, and the solar cell module realizes the power to the load P. Output.
Theoretical studies have shown that the peak power Pk of a solar cell module is determined by the local average solar radiation intensity and the end of the electrical load (required power).
(2) Electrical energy storage unit:
The direct current generated by the solar cell first enters the storage of the battery, and the characteristics of the battery affect the working efficiency and characteristics of the system. The battery technology is very mature, but its capacity is affected by the end of electricity demand, sunshine time (power generation time). Therefore, the battery watt hour capacity and ampere-hour capacity are determined by the predetermined continuous daylight-free time.
1.2 controller
The main function of the controller is to keep the solar power system near the maximum power point of power generation for maximum efficiency. The charging control usually adopts pulse width modulation technology, that is, PWM control mode, so that the whole system always runs in the vicinity of the maximum power point Pm. Discharge control mainly refers to when the battery is short of power and the system is faulty, such as when the battery is open or reversed. At present, Hitachi has developed a "sunflower" type controller that can track the control point Pm and track the solar movement parameters, and the efficiency of the fixed battery assembly is increased by about 50%.
1.3 DC-AC inverter:
Inverter can be divided into self-excited oscillation inverter and other excitation oscillation inverter according to the excitation mode. The main function is to invert the DC power of the battery into AC power. Through the full-bridge circuit, the SPWM processor is generally modulated, filtered, boosted, etc., and the sinusoidal alternating current matched with the lighting load frequency f and the rated voltage UN is used by the end user of the system.
2 Solar power system efficiency
In a solar power generation system, the total efficiency ηese of the system is composed of the PV conversion rate of the battery component, the controller efficiency, the battery efficiency, the efficiency of the inverter, and the efficiency of the load. However, compared with solar cell technology, the technology and production level of other units such as controllers, inverters and lighting loads are much more mature, and the current conversion rate of the system is only about 17%. Therefore, improving the conversion rate of battery components and reducing the unit cost are the key and difficult points of solar power industrialization. Since the advent of solar cells, crystalline silicon has maintained its dominance as a protagonist. At present, the research on the conversion rate of silicon cells mainly focuses on increasing the energy absorption surface, such as double-sided batteries, reducing reflection; using the gettering technology to reduce the compounding of semiconductor materials; the battery is ultra-thin; improving the theory and establishing a new model; Concentrated batteries, etc. The conversion efficiency of several solar cells is shown in Table 1.
Making full use of solar energy is one of the important contents of green lighting. In fact, the green lighting in the true sense includes at least: the high efficiency of the lighting system, high stability, and energy-efficient green light source.
3.1 Power Generation - Architectural Lighting Integration
At present, solar modules and building components have been successfully integrated, such as solar roofs (tops), walls, doors and windows, etc., to achieve "photovoltaic - architectural lighting integration (BIPV)." In June 1997, the United States announced the “Solar Million Roof Planâ€, named after the president, to implement a solar power system for 1 million homes by 2010. Japan's "New Sunshine Program" has reduced the installed cost of photovoltaic building components to 170-210 yen/W by 2000, the annual output of solar cells to 10MW, and the battery cost to 25-30 yen/W. On May 14, 1999, Germany built the world's first zero-emission solar cell module factory in just one year and two months. It supplies electricity entirely from renewable energy sources and does not emit CO2 during production. The south wall of the factory is a PV array glass curtain wall of about 10m high, including the roof PV module. The entire factory building is equipped with 575m2 solar modules, which can provide more than one-third of the power for the building, its wall and The combination of roof PV module shape, color, architectural style and building, and the integration with the surrounding natural environment have achieved perfect coordination. The building also has a capacity of about 45 kW. It is supplied by a thermal power plant fueled by natural vegetable oil. The CO2 produced by burning rapeseed oil is basically balanced with the CO2 required for the growth of rapeseed. It is a true zero-emission plant. BIPV also pays attention to the research of architectural decoration art. In the Czech Republic, the German WIP company cooperated with the Czech Republic to build the world's first color PV curtain wall. In West Bengal, India, 12.5 kW of BIPV was installed for 117 villagers in an island without electricity. Domestic Changzhou Tianhe Aluminum Plate Curtain Wall Manufacturing Co., Ltd. has successfully developed a “sun roomâ€, which integrates power generation, energy conservation, environmental protection and value-added into one room, and successfully combines optoelectronic technology with building technology, called Solar Building System (SPBS). SPBS was approved by experts on September 20, 2000. Recently, the first solar-integrated public toilet in China was built in Pudong, Shanghai. All electricity is supplied by rooftop solar cells. This will effectively promote the industrialization and marketization of solar energy building energy conservation.
3.2 Green lighting source research
The green lighting system is optimized to achieve high light output at low energy consumption and extend lamp life. Therefore, the DC-AC inverter design should obtain reasonable filament warm-up time and voltage and current waveforms of the excitation lamp. At present, there are four typical circuits for the excitation mode of solar lighting sources in research and development: 1 self-excited push-pull oscillation circuit, which is preheated by the filament series starter. The main parameters of the light source system are: input voltage DC=12V, output light efficiency>495Lm/branch, lamp rated efficiency 9W, effective life 3200h, continuous opening times>1000 times. 2 self-excited push-pull oscillation (simple) circuit, the main parameters of the light source system are: input voltage DC=12V, lamp power 9W, output light efficiency 315Lm/branch, continuous start times>1500 times. 3 self-excited single-tube oscillation circuit, filament series relay preheating start mode. 4 self-excited single-tube oscillation (simple) circuit and other efficient energy-saving green light source.
4 Conclusion
The issue of green energy and sustainable development is a major issue facing humanity in this century. The development of new energy sources and the full and rational use of existing energy sources have received great attention from governments. As an inexhaustible and clean energy source, solar power will be developed as never before. With the deepening of solar energy industrialization and technology development, its efficiency and cost performance will be improved. It will be widely used in various fields including BIPV, and will also greatly promote the rapid development of China's “green lighting projectâ€. development of.
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