With the rapid development of the global economy and the progress of mankind, people have made higher and higher demands on energy. The development of new energy has become an urgent issue for humankind. The
Because fossil-fired power needs to burn fossil fuels such as coal and oil, on the one hand, fossil fuels have limited reserves and are in danger of depletion. On the other hand, the burning of fuel will emit CO2 and sulfur oxides, which will lead to greenhouse effect and acid rain, which will worsen the global environment. Hydropower will inundate large amounts of land, which may cause damage to the ecological environment. In the event of a collapse of a large reservoir, the consequences will be disastrous. In addition, the hydropower resources of some countries are also limited, and they will also be affected by the season. Nuclear power is certainly clean under normal conditions, but in the event of a nuclear leak, the consequences are equally terrible.
The above problems are forcing people to find new energy sources. New energy must meet two conditions at the same time: First, it is rich in reserves and will not be exhausted; second, it is safe and clean, and it will not threaten humanity and destroy the environment. New energy sources currently found include: solar energy, wind energy, and fuel cells.
The sun that shines on the earth has enormous energy. Solar radiation on the earth for about 40 minutes is enough for humans to consume energy for a year. It can be said that solar energy is a truly inexhaustible source of energy. And solar power is absolutely clean and does not cause pollution. Therefore, solar power is an ideal energy source with a wide range of applications and bright prospects.
Second, the principle of solar power
Solar power generation utilizes the electrical properties of solar and semiconductor materials to generate electricity.
The principle of solar power generation (photovoltaic power generation): The sun shines on the semiconductor pn junction to form a new hole electron pair. Under the effect of the pn junction electric field, holes flow from the n region to the p region, and electrons flow from the p region to n. In the area, the current is formed after the circuit is turned on. This is the working principle of the photoelectric effect solar cell.
2. Two methods of solar power generation: one is light-heat-electric conversion, and the other is light-electric direct conversion.
a. Light-heat-electricity conversion method: By utilizing the heat energy generated by solar radiation to generate electricity, a solar energy collector converts the absorbed thermal energy into vapor of the working fluid, and then drives the turbine to generate electricity. The former process is a light-heat conversion process; the latter process is a thermal-electric conversion process, just like ordinary thermal power generation. The disadvantage of solar thermal power generation is its low efficiency and high cost. It is estimated that its investment is at least lower than that of ordinary fires. The power station is 5 to 10 times more expensive. A 1,000MW solar thermal power plant needs investment of 200 to 250 million U.S. dollars, and an average investment of 1kW is 2000 to 2500 U.S. dollars. Therefore, it can only be applied to special occasions on a small scale. Large-scale use is economically uneconomical and cannot compete with ordinary thermal power plants or nuclear power plants.
b. Light-electricity direct conversion method (photovoltaic power generation): The photoelectric effect is used to convert solar radiation energy directly into electrical energy. The basic device for light-to-electrical conversion is a solar cell. A solar cell is a device that converts solar energy directly into electrical energy due to the photovoltaic effect. It is a semiconductor photodiode. When the sun shines on a photodiode, the photodiode turns the light energy of the sun into electricity. Figure) This method is easy to implement, and its cost is low. It has been widely used.
Materials that can produce photovoltaic effect: monocrystalline silicon, polysilicon, amorphous silicon, gallium arsenide, selenium indium copper, etc. P-type crystalline silicon can obtain N-type silicon through doping with phosphorus to form a P-N junction. Crystalline silicon is the basic battery material. Solar cells made of crystalline silicon materials mainly include: monocrystalline silicon solar cells, cast polysilicon solar cells, amorphous silicon solar cells, and thin film crystalline silicon cells. Monocrystalline silicon cells have high battery conversion efficiency and good stability, but the cost is higher. Amorphous silicon solar cells have high production efficiency and low cost, but the conversion efficiency is low, and the efficiency decays faster; casting polysilicon solar cells It has a stable conversion efficiency, and the highest price-performance ratio; thin film crystalline silicon solar cells are in the R & D stage. Among the silicon series solar cells, monocrystalline silicon and polycrystalline silicon cells continue to dominate the photovoltaic market, and the proportion of monocrystalline silicon and polysilicon has exceeded 80%.
Solar cell production process can be roughly divided into five steps: a, purification process b, pull rod process c, slicing process d, battery process e, packaging process.
3, the process of solar power generation:
Crystals are now used as an example to describe the process of photovoltaic power generation. When the light shines on the surface of the solar cell, some of the photons are absorbed by the silicon material; the energy of the photons is transmitted to the silicon atoms, causing the electrons to migrate. The free electrons accumulate on both sides of the P-N junction to form a potential difference when externally connected. In the circuit, under the action of this voltage, there will be a current flowing through the external circuit to generate a certain output power. When many cells are connected in series or in parallel, a solar cell array with a large output power can be formed.
Third, solar power system
1. The composition of the solar power system: The solar power system is mainly composed of a solar panel, a charging controller, an inverter and a battery. (Figure) Below is a brief introduction to the functions of each part:
Solar panels: The role is to convert solar radiation directly into direct current for use by the load or for storage in the battery. Generally, according to the needs of the user, a number of solar panels are connected in a certain manner to form a solar cell array, and then a suitable bracket and junction box are formed.
Charge Controller: The charge controller consists of a dedicated processor CPU, electronic components, displays, and switching power transistors. In the solar power generation system, the basic role of the charge controller is to provide the best charging current and voltage for the battery, to quickly, smoothly and efficiently charge the battery, and to reduce the loss during the charging process, to extend the service life of the battery; Protect the battery from over-charging and over-discharging. At the same time, it records and displays various important data of the system, such as charging current and voltage. When the performance of the controller is not good, the service life of the battery has a great influence, and ultimately affects the reliability of the system.
Inverter: The function is to reverse the direct current provided by the solar cell square array and the battery to alternating current, and to use it for AC load and incorporate into the grid. Efficiency is one of the important criteria for selecting an inverter. The higher the efficiency, the less power loss is generated in the process of converting direct current generated by photovoltaic components into alternating current. The quality of the inverter determines the efficiency of the power generation system, which is the core of the solar power system.
Battery pack: The role is to send solar energy to the solar array and store it for use by the load. In a photovoltaic power generation system, the battery is in a floating charge discharge state. During the day, the solar cell matrix charges the battery, while the square array returns power to the load. At night, all the load power is supplied by the battery. Therefore, the self-discharge of the battery is required to be small, and the charging efficiency is high. At the same time, it is also necessary to consider factors such as price and ease of use.
2. Operation mode of solar power system: solar power system has DC power supply, AC power supply, AC and DC power supply,
Off-grid operation, grid-connected operation, wind-solar hybrid operation, several operation methods (pictured)
DC power supply system: After the solar energy controller adjusts and controls the emitted power, it is directly sent to the DC load, and the surplus part is sent to the battery for storage.
AC power supply system: After the solar energy controller adjusts and controls the emitted power, it passes through the inverter and sends it to the AC load. The excess energy is sent to the battery bank for storage.
Off-grid power generation system: The solar power controller (photovoltaic controller and wind-solar hybrid controller) regulates and controls the generated power. On the one hand, the adjusted energy is sent to the DC load or sent to the AC load through the inverter. On the other hand, excess energy is sent to the battery pack for storage. When the generated electricity cannot meet the load requirements, the controller sends the battery's power to the load. (Figure 4 DC power supply, AC and DC power supply, wind and solar power generation are all off-grid power generation systems)
Grid-connected power generation system: The energy generated by solar power generation is stored in the power generation system of the power grid through the grid-connected inverter without energy storage in the battery. Because electric energy is directly input into the power grid, the configuration of the battery is eliminated, the process of storing and releasing the battery is omitted, the power generated by the solar energy can be fully utilized, the energy loss can be reduced, and the system cost can be reduced. The grid-connected power generation system can use the commercial power and solar power generation in parallel as the power source of the local alternating current load and reduce the load shortage rate of the entire system. At the same time, grid-connected systems can play a role in peaking the utility grid. The grid-connected power generation system is the development direction of solar power generation and represents the most attractive energy utilization technology in the 21st century.
Fourth, the characteristics of solar power:
1 Solar energy is a permanent energy source and there is no risk of depletion;
2 Solar energy is clean energy. It is absolutely clean and environmentally friendly. It has no pollution, and users are emotionally easy to accept.
3 The use of solar power is flexible, and it is not limited by the resources and geographical distribution.
4 The solar battery has a long life, and can be used for long-term investment. The solar battery can be used in large, medium, and small scales, with medium-sized power plants up to 1 million kilowatts, and solar cells that are small enough for only one household.
5 High reliability of solar power generation and high energy quality;
6 It takes a short time to get energy.
1 The energy distribution density of the irradiation is small and it needs to occupy a huge area;
2 The energy obtained is affected by the meteorological conditions such as the four seasons, day and night, and overcast weather.
V. Application and Development Prospects of Solar Power
1, the application of solar power:
With the continuous increase in the number of solar cells, the application of a wide range, the market gradually expanded. In the early days, the use of solar energy was mainly used in the military and aerospace fields. At present, solar energy has entered the industrial, commercial, agricultural, communications, household appliances and utilities and other departments. The application of solar power is divided into several aspects: small-scale solar power plants for home use, large-scale grid-connected power stations, integrated photovoltaic glass curtain walls, solar street lights, wind-solar hybrid street lights, wind-solar hybrid power supply systems, etc. For example: solar garden lights; solar power user systems In particular, independent systems for village power supply can be used in remote areas, mountains, deserts, islands and rural areas to save costly transmission lines; photovoltaic pumps (drinking water or irrigation); communication power; cathodic protection of oil pipelines; Fiber-optic cable station power supply; seawater desalination system; road signs in towns; highway signposts, etc.
The potential for solar photovoltaic power generation is huge. It is one of the most sustainable renewable energy technologies.
At present, although China's solar photovoltaic power generation technology has matured, it is necessary to make real use of solar power generation to provide the driving force for the long-term development of this new energy source. We must also improve the following aspects:
1, increase the scale of production, improve the level of technology, improve product quality;
2. Improve solar photoelectric conversion efficiency and reduce product production costs;
3. Really realize the grid-connected operation of solar power generation and the existing power grid.
Vigorously developing new energy and renewable energy is China's future energy development strategy. Due to the increasing tension in the world's energy and the continuous development of photovoltaic technology, maximizing the development and utilization of solar energy will be the development direction of humankind's new energy use. Only relying on more advanced science and technology can open up vast prospects for the future use of solar energy on a large scale.
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