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Solar power is a device that uses a battery pack to convert solar energy directly into electrical energy. Solar cells are solid-state devices that use the electronic properties of semiconductor materials to realize PV conversion. In a large area without electricity grids, the device can be conveniently used for lighting and living for users. Some developed countries can also use the regional grid. Grid to achieve complementarity. At present, from the perspective of civil use, the technology research in foreign countries tends to be mature and has begun to industrialize. It is a photovoltaic-architecture (lighting) integration technology, while domestic research and production mainly applies to small-scale solar power generation systems for household lighting in areas where electricity is not available.
1 Principle of solar power generation
The solar power generation system mainly includes: solar battery components (arrays), controllers, batteries, inverters, and users, ie, lighting loads. Among them, the solar battery module and the battery are the power supply system, the controller and the inverter are the control protection systems, and the load is the system terminal.
1.1 Solar Power System
The solar battery and the battery constitute the power supply unit of the system, so the battery performance directly affects the system operating characteristics.
(1) Battery unit
Due to technical and material reasons, the amount of electricity generated by a single battery is very limited. In practice, a solar battery is a battery system in which a single battery is composed of strings and parallels, and is called a battery module (array). The single cell is a silicon crystal diode. According to the electronic characteristics of the semiconductor material, when the sun shines on the pn junction made of p-type and n-type homogenous semiconductor materials of different conductivity types, under certain conditions Solar radiation is absorbed by the semiconductor material, resulting in non-equilibrium carriers, electrons and holes, in the conduction band and valence band. Similar to 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 a photocurrent flows through the loop formed by the PN junction, the connecting circuit, and the load, and the solar cell module realizes the power P output to the load.
Theoretical research shows that the peak power Pk of a solar cell module is determined by the local average solar radiation intensity and the end-use electrical load (electricity demand).
( 2) Electrical energy storage unit
The direct current generated by solar cells enters the battery first, and the characteristics of the battery affect the efficiency and characteristics of the system. The battery technology is very mature, but its capacity is affected by the amount of power required at the end of the day and the duration of the sunshine (power generation time). Therefore, the battery watt-hour capacity and ampere-hour capacity are determined by the predetermined continuous no-sunlight time.
1.2 Controller
The main function of the controller is to make the solar power system always in the vicinity of the maximum power point of power generation in order to obtain the highest efficiency. The charge control usually adopts pulse width modulation technology, ie, PWM control mode, so that the entire system always runs in the area near the maximum power point Pm. Discharge control mainly refers to the lack of electricity in the battery, system failure, such as the battery open or reversed switch off. At present, Hitachi has developed a sunflower-type controller that can both track the control point Pm and track the sun's movement parameters, which increases the efficiency of the fixed battery module by about 50%.
1.3 DC-AC Inverter
The inverter can be divided into self-excited oscillation inverter and he-excited oscillation inverter according to the excitation method. The main function is to reverse the DC power of the battery into AC power. Through a full-bridge circuit, the SPWM processor is generally used to modulate, filter, boost, etc., to obtain the sinusoidal AC power supply system end users that match the lighting load frequency f and the rated voltage UN.
2 Efficiency of Solar Power System
In a solar power system, the total system efficiency ηesee consists of the PV module conversion rate, controller efficiency, battery efficiency, inverter efficiency, and load efficiency. However, compared to solar cell technology, it is much more mature than the technology and production levels of other units such as controllers, inverters, and lighting loads, and the current system conversion rate is only about 17%. 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. Since the advent of solar cells, crystalline silicon has maintained its dominance as the leading material. The current research on the conversion rate of silicon cells mainly revolves around increasing the energy-absorbing surface, such as double-sided batteries, to reduce reflections; using gettering technology to reduce the recombination of semiconductor materials; thinning the battery; improving theory and establishing a new model; Spotlight batteries. The conversion efficiency of several solar cells is shown in Table 1.
Table 1 Conversion Efficiency of Several Solar Cells
Lab typical battery Commercial thin film battery
Various Solar Cells ηmax(%) Various Solar Cells η(%)
Monocrystalline 24.4 Polysilicon 16.6
Polysilicon 18.6 Copper Indium Gallium Selenide 18.8
GaAs (Single Junction) 25.7 Cadmium Telluride 16.0
A-si (single junction) 13 copper indium and selenium 14.1
Making full use of solar energy is one of the important contents of green lighting. The true sense of green lighting includes at least: the lighting system's high efficiency, high stability, and energy-efficient green light sources.
3.1 Power Generation - Building Lighting Integration
At present, solar modules and building components have been successfully integrated, such as solar roofs (tops), walls, doors, windows, etc., to achieve the integration of photovoltaic-building lighting (BIPV). In June 1997, the United States announced the solar million solar roof project named after the president and implemented solar power generation systems for one million homes by 2010. Japan's New Sunshine Project has reduced the installed cost of photovoltaic building components to 170-210 yen/W by 2000, and the annual output of solar cells has reached 10MW, and the cost of batteries has dropped to 25-30 yen/W. On May 14, 1999, Germany built the world's first zero-emission solar cell module plant in just one year and two months, completely supplying electricity with renewable energy, and not emitting CO2 during production. The south wall of the factory is about 10m high PV array glass curtain wall, including the roof PV module, the entire factory building is equipped with 575m2 solar module, this can provide more than one third of the electric energy for the building, and its wall surface The combination of the shape, color, architectural style, and architecture of the roof PV assembly achieves perfect coordination with the surrounding natural environment. The building also has a capacity of about 45kW, which is provided by a thermal power plant fueled with natural rapeseed oil. The CO2 that is produced when the rapeseed oil is burned and the CO2 required for the growth of rapeseed is basically a zero-emission plant in a true sense. BIPV also pays attention to the research of architectural decoration art. In Czech, the German WIP company cooperated with the Czech Republic to build the world's first color PV curtain wall. India's West Bengal installed 12.5kW BIPV for 117 villagers on an island without electricity. Domestic Changzhou Tianhe Aluminum Curtain Wall Manufacturing Co., Ltd. has successfully developed a solar house that integrates power generation, energy saving, environmental protection, and value-added in one room. It successfully combines photovoltaic technology and building technology. It is called the solar building system (SPBS), SPBS. It was approved by experts on September 20, 2000. Recently, the first solar-lighted integrated public toilet in China was built in Pudong, Shanghai. All the electricity is provided by rooftop solar cells. This will effectively promote the industrialization and marketization of solar building energy efficiency.
3.2 Green Lighting Source Study
The optimal design of the green lighting system requires high light output with low energy consumption and extended lamp life. Therefore, DC-AC inverter design should obtain reasonable filament warm-up time and excitation lamp voltage and current waveforms. At present, there are four typical circuits for the solar illumination light source excitation method in research and development: 1 Self-excited push-pull oscillation circuit, which is started through a filament filament series starter. The main parameters of the light source system are: input voltage DC = 12V, output light efficiency> 495Lm / support, lamp rated efficiency 9W, effective life 3200h, continuous opening times> 1000 times. 2 self-excited push-pull oscillation (simple type) circuit, the main parameters of the light source system are: input voltage DC = 12V, lamp power 9W, output light efficiency 315Lm / support, continuous start times> 1500 times. 3 self-excited single-tube oscillation circuit, filament series relay warm-up start mode. 4 Efficient and energy-saving green light sources such as self-excited single-tube oscillation (simple type) circuits.
4 Conclusion
The issue of green energy and sustainable development is a major issue facing humankind in this century. The development of new energy sources and the full and reasonable use of existing energy resources have received great attention from governments of all countries. As an inexhaustible source of solar energy, the inexhaustible clean and environmentally friendly energy source will have unprecedented development. With the deepening of solar energy industrialization process and technology development, its efficiency and cost performance will be improved. It will be widely used in various fields including BIPV, and it will also greatly promote the rapid development of China's green lighting project.
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