With the rapid development of the global economy and the progress of mankind, people have put forward higher and higher requirements for energy, and the development of new energy has become an urgent issue facing mankind.
Because thermal power needs to burn fossil fuels such as coal and oil, on the one hand, fossil fuel reserves are limited and are facing the danger of exhaustion. On the other hand, burning fuel will emit CO2 and sulfur oxides, which will cause the greenhouse effect and acid rain, which will deteriorate the global environment. Hydropower will inundate a large amount of land, which may cause damage to the ecological environment, and once a large reservoir collapses, the consequences will be unimaginable. In addition, some countries have limited water resources and are affected by the seasons. Although nuclear power is clean under normal circumstances, in the event of a nuclear leak, the consequences are equally terrible.
The above problems have forced 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 will not threaten humans and damage the environment. The new energy sources currently found are: solar energy, wind energy, and fuel cells.
The energy of the sun shining on the earth is very huge, and the solar energy shining on the earth for about 40 minutes is enough for the energy consumption of human beings all over the world. It can be said that solar energy is truly inexhaustible and inexhaustible energy. Moreover, solar power generation is absolutely clean and does not cause pollution. Therefore, solar power generation is an ideal energy with a wide range of applications and a bright future .
2. The principle of solar power generation
Solar power generation uses the electronic properties of solar energy and semiconductor materials to generate electricity.
1. The principle of solar power generation (photovoltaic power generation): sunlight shines on the semiconductor pn junction to form new hole-electron pairs. Under the action of the pn junction electric field, holes flow from the n zone to the p zone, and electrons from the p zone to the n Area, after the circuit is turned on, a current is formed. This is the working principle of photovoltaic effect solar cells. (Picture 🙂
2. There are 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: generating electricity by using the thermal energy generated by solar radiation. Generally, the solar collector converts the absorbed thermal energy into the vapor of the working fluid, and then drives the steam turbine to generate electricity. The former process is a light -heat conversion process; the latter process is a heat-electric conversion process, which is the same as ordinary thermal power generation. The disadvantages of solar thermal power generation are its low efficiency and high cost. It is estimated that its investment is at least higher than that of ordinary thermal power generation. The power station is 5-10 times more expensive. A 1000MW solar thermal power station requires an investment of 2 to 2.5 billion US dollars, and the average investment for 1 kW is 2000 to 2500 US dollars. Therefore, it can only be applied to special occasions on a small scale at present, and large-scale utilization is very 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 directly convert solar radiation energy into electrical energy. The basic device of light -electric conversion is solar cell. A solar cell is a device that directly converts sunlight energy into electrical energy due to the photovoltaic effect. It is a semiconductor photodiode. When the sun shines on the photodiode, the photodiode will turn the sun’s light energy into electrical energy (such as Figure), this method is easy to implement and low cost, has been widely used.
Materials that can produce photovoltaic effect: monocrystalline silicon, polycrystalline silicon, amorphous silicon, gallium arsenide, indium selenium copper, etc. P-type crystalline silicon can be doped with phosphorus to obtain N-type silicon, forming 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 polycrystalline silicon solar cells, amorphous silicon solar cells and thin-film crystalline silicon cells. Monocrystalline silicon cells have high cell conversion efficiency, good stability, but high cost; amorphous silicon solar cells have high production efficiency and low cost, but the conversion efficiency is low, and the efficiency decays faster; cast polycrystalline silicon solar cells It has stable conversion efficiency and the highest performance-price ratio; thin-film crystalline silicon solar cells are in the research and development stage. Among the silicon solar cells, monocrystalline silicon and polycrystalline silicon cells continue to dominate the photovoltaic market, and the proportion of monocrystalline silicon and polycrystalline silicon has exceeded 80% .
The production process of solar cells can be roughly divided into five steps: a, purification process b, drawing process c, slicing process d, battery making process e, packaging process.
3. The process of solar power generation:
Take crystal as an example to describe the process of photovoltaic power generation. When the light irradiates the surface of the solar cell, part of the photons are absorbed by the silicon material; the energy of the photons is transferred to the silicon atoms, causing the electrons to transition, and the free electrons gather on the two sides of the PN junction to form a potential difference. In the circuit, under the action of this voltage, a current will flow through the external circuit to produce a certain output power. When many batteries are connected in series or in parallel, a square array of solar cells with larger output power can be formed.
3. Solar power system
1. Composition of solar power generation system : The solar power generation system is mainly composed of solar panels, charge controllers, inverters and batteries. (As shown in the figure ) The following is a brief introduction to the functions of each part:
Solar panels: The function is to directly convert solar radiation energy into direct current for use by loads or stored in batteries for backup. Generally, according to user needs, a number of solar panels are connected in a certain way to form a solar cell array, which is then equipped with appropriate brackets and junction boxes.
Charge controller: The charge controller is mainly composed of dedicated processor CPU, electronic components, display, switch power tube, etc. In the solar power system, the basic function of the charge controller is to provide the battery with the best charging current and voltage, charge the battery quickly, smoothly, and efficiently, reduce loss during the charging process, and maximize the service life of the battery; at the same time; Protect the battery to avoid overcharge and overdischarge. 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, it will have a great impact on the service life of the battery, and ultimately affect the reliability of the system.
Inverter: The function is to invert the DC power provided by the solar cell array and the storage battery into AC power, which is used by the AC load and integrated 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 the direct current generated by the optoelectronic component into alternating current. The quality of the inverter determines the benefit of the power generation system, and it is the core of the solar power generation system.
Battery: the role of the square solar cells is sent up DC energy storage , for load. In the photovoltaic power generation system , the battery is in a floating charge and discharge state. During the day, the solar cell phalanx charges the battery , while the phalanx also supplies electricity to the load . At night, all the load electricity is supplied by the battery. Therefore , the self-discharge of the battery is required to be small , and the charging efficiency should be high . At the same time, factors such as price and convenience of use must also be considered.
2. Operation mode of solar power system : solar power system has DC power supply, AC power supply, AC and DC power supply,
Several operation modes of off-grid operation, grid-connected operation, and wind-solar hybrid operation (see picture )
DC power supply system: After the solar power controller adjusts and controls the generated electric energy, it is directly sent to the DC load, and the excess part is sent to the storage battery.
AC power supply system: After the solar power controller regulates and controls the generated electric energy, it is sent to the AC load through the inverter, and the excess energy is sent to the storage battery pack.
Off-grid power generation system: The solar power controller ( photovoltaic controller and wind-solar hybrid controller ) regulates and controls the generated electric energy. On the one hand, the adjusted energy is sent to the DC load or the inverter to the AC load. On the other hand, the surplus energy is sent to the battery pack for storage. When the generated electricity cannot meet the needs of the load, the controller sends the energy of the battery to the load. ( The DC power supply, AC and DC power supply, and wind and solar hybrid power generation in Figure 4 are all off-grid power generation systems)
Grid-connected power generation system: A power generation system that directly feeds the electricity generated by solar power into the grid through a grid-connected inverter without storing energy in a battery. Because the electrical energy is directly input to the grid, the battery is not required, and the process of storage and release of the battery is eliminated. The electricity generated by the solar energy can be fully utilized to reduce energy loss and reduce system costs. The grid-connected power generation system can use city power and solar power in parallel as the power source of the local AC load, reducing the load shortage rate of the entire system. At the same time, the grid-connected system can play a role in peak regulation of the public grid. 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 generation:
1. Advantages:
① Solar energy is a permanent energy source, and there is no danger of exhaustion;
②Solar energy is a clean energy source, absolutely clean and environmentally friendly, without pollution, and easily accepted by users emotionally;
③Solar power generation can be used flexibly, not limited by resource distribution and geographical location, and can generate electricity near the place where the electricity is used;
④The solar battery has a long service life and can be used for a long time with one investment. The solar battery can be large, medium and small, as large as a million kilowatt medium-sized power station, or as small as a solar battery pack for only one household;
⑤Solar power generation has high reliability and high energy quality;
⑥ It takes a short time to obtain energy.
2. Disadvantages:
① The irradiated energy distribution density is small and needs to occupy a huge area;
② The energy obtained is affected by weather conditions such as four seasons, day and night, overcast and sunny.
5. Application and development prospects of solar power
1. Application of solar power generation :
As the types of solar cells continue to increase, the scope of application is increasingly broad, and the market scale is gradually expanding. 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 sectors of industry, commerce, agriculture, communications, household appliances, and public facilities. Solar power applications are divided into several aspects: small household solar power stations, large grid-connected power stations, building-integrated photovoltaic glass curtain walls, solar street lights, wind-solar hybrid street lamps, wind-solar hybrid power supply systems, etc., such as: solar garden lights; solar power user systems In particular, the independent power supply system of the village can be used in remote areas, mountains, deserts, islands and rural areas to save expensive transmission lines ; there are photovoltaic water pumps (drinking water or irrigation); communication power supply; oil pipeline cathodic protection; Optical fiber communication station power supply; seawater desalination system; road signs in towns; highway road signs, etc. (Pictured )
2. Research status and development prospects of solar power
a . Current status and prospects of foreign solar photovoltaic power generation :
At present, a total of 136 countries around the world have invested in the popularization and application of solar cells . Among them, 95 countries are conducting large-scale research and development of solar power and solar cells , and actively producing various related energy-saving new products. There are nearly 200 . the company produces solar cells, 1998 Nian , the world production of solar cells , its total power generation capacity of 1000 MW 1999 Nian up to 2850 MW. 2000 Nian , the world’s nearly 4600 manufacturers to provide photovoltaic cells and the light battery-powered products to the market. The production of solar cells worldwide has increased by nearly 40% annually on average . The production scale has grown from 1 to 5 MW / year to 5 to 25 MW / year, and is expanding to 50 MW or even 100 MW.
Since this century, some developed countries have formulated plans to develop renewable energy including solar cells. The research and production of solar cells has spread on a large scale in Europe, America, and Asia. India is in a leading position, with a cumulative installed capacity of approximately 40 MW. The United States and Japan are competing to issue research and development plans for solar technology. In 2010 , the United States plans to install 4,600 megawatts ( including the million roof plan ); Japan plans to install 5000 megawatts (NEDO Japan New Sunshine Plan ) . A recent survey of the photovoltaic industry shows that by 2010 , the annual growth rate of the photovoltaic industry will remain above 30% . Pike Research forecasts that PV will 2010 bring the end of 120 gigawatts of capacity, well in excess of Pike Research expects 2010 Nian 101 gigawatts of demand.
In terms of solar power generation technology, all countries have new inventions and ideas, such as:
Texas Instruments and SCE has developed a new solar cell, each cell having a diameter of less than 1 mm beads, distributed in the soft aluminum foil, about 50 distributed over an area cm 1 , 700 th Small unit. Its characteristic is that although the conversion efficiency is only 8 % -10% , it is cheap, the aluminum foil backing is soft and strong, can be folded at will and is durable, and it can generate electricity when hung in the sun, and it is convenient to use. The cost is low. The equipment with generating capacity per watt only costs 15 to 2 dollars, and the cost of each kilowatt -hour of electricity is about 14 cents, which can compete with the electricity generated by ordinary power plants. Hang this kind of battery on the sunny roof and wall, you can get one to two thousand kilowatt-hours of electricity every year.
Japan’s Genesis Plan: Prepare to use the desert and ocean areas on the ground to generate electricity, and connect global solar power stations to a unified power grid through superconducting cables to provide power to the world. It is estimated that 2000 year 2050 year 2100 year even if the whole global energy supply with solar power, but also as an area of 65.11 square kilometers, 186.79 square kilometers, 829.19 square kilometers. Only 8,291,900 square kilometers accounted for 2.3 % of the total ocean area or 51.4 % of the total desert . This plan is possible.
NASA and the Department of Energy proposed an idea: to build a solar power station in space, plan to put a large flat plate 10 kilometers long and 5 kilometers wide on a synchronous orbit , covered with solar cells, so that it can provide 5 million kilowatts of electricity. But this needs to solve the problem of wireless transmission to the ground. But there is still a long way to go before it is truly practical.
b . Current status and development prospects of domestic solar photovoltaic power generation:
China’s solar power generation industry has a considerable scale, and the technical conditions have become mature. The use of solar energy will be the most feasible solution for China’s energy reform.
As early as the Seventh Five-Year Plan period , the research work of amorphous silicon semiconductors has been listed as a major national topic ; during the Eighth Five-Year Plan and the Ninth Five-Year Plan period , China focused its research and development on large-area solar cells. 2003 years 10 months, the national 5 -year solar energy resources development program, fund-raising 100 million yuan for promoting the application of solar power technology, the 2005 National solar power systems with a total capacity of 300 MW.
In 2002 , the state launched the ” Electricity Program for Non-Electric Townships in Western Provinces and Regions ” , and adopted solar and small wind power generation to solve the electricity problem of electricity-free villages in the seven western provinces and regions.
In the 1990s , the domestic photovoltaic market developed steadily, with an annual growth rate of about 20% . In the 21st century, the domestic photovoltaic market showed an accelerated development trend, with an average growth rate of more than 30% from 2001 to 2003 . According to China’s “New Energy and Renewable Energy Development Plan” plan, China installed 70 MW of photovoltaic systems in rural power grid construction from 2003 to 2009 , and will be popularized and applied from 2010 to 2020 , with an average annual installation of 100 MW.
At present, China is already an international production base for photovoltaic power generation applications. Has 10 solar cell production line , the annual production capacity of about 4.5MW , experts predict that from 2011 the beginning of , China’s PV market demand will be greater than 20MW .
In the next ten years, the market trend of solar cells will undergo great changes. Before 2010 , most solar cells in China were used in independent photovoltaic power generation systems. From 2011 to 2020 , the mainstream of China’s photovoltaic power generation market will be From independent power generation systems to grid-connected power generation systems, including desert power stations and urban rooftop power generation systems.
Six, summary
The development potential of solar photovoltaic power generation is huge. It is one of the most sustainable renewable energy technologies.
Although my country’s solar photovoltaic power generation technology has matured day by day, the following aspects must be improved in order for solar power generation to be truly utilized and provide the driving force for the long-term development of this new energy:
1. Increase production scale, improve technical level, and improve product quality;
2. Improve the conversion efficiency of solar energy and reduce the production cost of products;
3. Realize the grid-connected operation of solar power generation and the existing power grid.
Vigorously developing new energy and renewable energy is a strategic requirement for my country’s future energy development. Due to the increasing shortage of world energy and the continuous development of photovoltaic technology, maximizing the development and utilization of solar energy will be the scientific and technological development direction of human new energy utilization. Only by relying on more advanced technology can it open up broad prospects for the large-scale use of solar energy in the future.