Solar cells are devices that directly convert light energy into electric energy through photoelectric effect or photochemical effect.
[Edit this paragraph] The principle of solar cells
Sunlight shines on the semiconductor pn junction, forming a new hole-electron pair. Under the action of pn junction electric field, holes flow from N region to P region, and electrons flow from P region to N region. When the circuit is connected, a current is formed. This is the working principle of photoelectric effect solar cells.
I. Solar power generation mode There are two ways of solar power generation, one is the light-heat-electricity conversion mode, and the other is the light-electricity direct conversion mode.
(1) The optical-thermal-electrical conversion mode uses the thermal energy generated by solar radiation to generate electricity. Generally, the absorbed heat energy is converted into working medium steam by solar collectors, and then the steam turbine is driven to generate electricity. The former process is photothermal conversion process; The latter process is a thermoelectric conversion process, just like ordinary thermal power generation. The disadvantages of solar thermal power generation are low efficiency and high cost. It is estimated that its investment is at least 5 ~ 10 times more expensive than that of ordinary thermal power plants. A solar thermal power plant with a capacity of 1000MW needs to invest 2-25 billion USD, and the average investment of 1kW is 2,000-25,000 USD. Therefore, at present, it can only be used in small-scale special occasions, and large-scale utilization is not economical and cannot compete with ordinary thermal power plants or nuclear power plants.
(2) photoelectric direct conversion mode This mode directly converts solar radiation energy into electric energy by photoelectric effect, and the basic device of photoelectric conversion is solar cell. Solar cell is a device that directly converts solar energy into electric energy due to photovoltaic effect, and it is a semiconductor photodiode. When the sun shines on the photodiode, the photodiode will convert solar energy into electric energy and generate current. When a plurality of batteries are connected in series or in parallel, it can become a solar cell array with relatively high output power. Solar cell is a promising new power supply, which has three advantages: permanence, cleanness and flexibility. Solar cells have a long life, and as long as the sun exists, they can be used for a long time at a time. Compared with thermal power generation and nuclear power generation, solar cells will not cause environmental pollution; Solar cells are large, medium and small, ranging from medium-sized power stations with a million kilowatts to solar cells that can only be used by one family, which are unmatched by other power sources.
[Edit this paragraph] Current situation of solar cell industry
At present, thin-film solar cells working with photoelectric effect are the mainstream, while wet-type solar cells working with photochemical effect are still in the embryonic stage.
Present situation of battery industry in global solar
According to the statistics of Dataquest, at present, there are 136 countries in the world, among which 95 countries are developing solar cells on a large scale and actively producing various related energy-saving new products. 1998 The total power generation of solar cells produced in the world reached 1000 MW, and 1999 reached 2850 MW. In 2000, nearly 4,600 manufacturers around the world provided photovoltaic cells and products powered by photovoltaic cells to the market.
At present, many countries are making medium and long-term solar energy development plans, preparing to develop solar energy on a large scale in 2 1 century. The U.S. Department of Energy launched the National Photovoltaic Program, and Japan launched the Sunshine Program. The NREL photovoltaic plan is an important part of the national photovoltaic plan of the United States. The plan carries out research work in five areas: monocrystalline silicon and advanced devices, thin film photovoltaic technology, PVMaT, photovoltaic modules, system performance and engineering, photovoltaic application and market development.
The United States has also launched the "Solar Street Lamp Program", aiming at changing street lamps in some cities in the United States to solar power supply. According to the plan, each street lamp can save electricity by 800 degrees per year. Japan is also implementing "70,000 solar energy projects". The solar residential power generation system to be popularized in Japan is mainly solar cell power generation equipment installed on the roof of the house, and the surplus electricity used by households can also be sold to power companies. A standard home can install a system that generates 3000 watts. In Europe, the research and development of solar cells was included in the famous "Eureka" high-tech plan, and "654.38+10,000 sets of engineering plan" was launched. These "solar projects" with the popularization and application of photovoltaic cells as the main content are one of the important driving forces to promote the great development of solar photovoltaic cell industry at present.
Japan, South Korea and eight European countries recently decided to cooperate to build the world's largest solar power station in inland Asia and desert areas in Africa. Their goal is to effectively use the long-term sunshine resources in desert areas, which account for about 1 4 of the global land area, and provide110,000 kilowatts of electricity for 300,000 users. The plan will start from 200 1 and take 4 years to complete.
At present, the United States and Japan have the largest share of photovoltaic market in the world. The United States has the world's largest photovoltaic power station with a power of 7MW, and Japan has also built a photovoltaic power station with a power of 1mw. There are 230,000 photovoltaic devices in the world, with Israel, Australia and New Zealand leading the way.
Since 1990s, the battery industry in global solar has been developing continuously with an annual growth rate of 15%. According to the latest statistics and forecast report released by Dataquest, from 65438 to 0998, the total investment of the United States, Japan and western European industrialized countries in solar energy research and development reached 57 billion dollars. 1999 was $654.38+64.6 billion; $70 billion in 2000; 200 1 year will reach $82 billion; It is estimated that it will exceed $6,543.8 trillion in 2002.
Present situation of solar cell industry in China
China attaches great importance to the research and development of solar cells. As early as the Seventh Five-Year Plan period, the research of amorphous silicon semiconductor was included in the national major topic. During the Eighth Five-Year Plan and the Ninth Five-Year Plan, the research and development of China focused on large-area solar cells. In June 2003, 5438+ 10, the National Development and Reform Commission and the Ministry of Science and Technology formulated the development plan of solar energy resources in the next five years. The "Bright Project" of the National Development and Reform Commission will raise10 billion yuan to promote the application of solar power generation technology. It is planned that the total installed capacity of solar power generation system in China will reach 300 MW by 2005.
In 2002, the relevant ministries and commissions of the state launched the "plan to electrify villages without electricity in the west" to solve the problem of electricity consumption in villages without electricity in seven western provinces through solar energy and small wind power generation. The start of this project has greatly stimulated the solar power generation industry, and a number of solar cell packaging lines have been built in China, which has rapidly increased the annual output of solar cells. At present, there are 10 solar cell production lines in China, with an annual production capacity of about 4.5MW, of which 8 production lines are imported from abroad. Among these eight production lines, there are 6 monocrystalline silicon solar cell production lines and 2 amorphous silicon solar cell production lines. According to experts' prediction, the current photovoltaic market demand in China is 5 MW per year. From 200 1 to 20 10, the annual demand will reach 100 MW. Starting from 20 1 1, the annual demand of photovoltaic market in China will be greater than 20MW.
At present, domestic solar monocrystalline silicon producers mainly include Luoyang monocrystalline silicon factory, Hebei Ningjin monocrystalline silicon base and Sichuan Emei semiconductor material factory, among which Hebei Ningjin monocrystalline silicon base is the largest solar monocrystalline silicon production base in the world, accounting for about 25% of the world solar monocrystalline silicon market share.
In the downstream market of solar cell materials, at present, domestic solar cell manufacturers mainly include Wuxi Suntech, Nanjing Zhongdian, Baoding Yingli, Hebei Jingao, Jieni New Energy, Suzhou Artes, Changzhou Tianhe, Yunnan Tianda Photovoltaic Technology, Ningbo Solar, Kyocera (Tianjin) Solar and other companies, with a total annual production capacity of over 800MW.
Analysis of solar cells and the prospect of solar power generation
At present, the application of solar cells has entered the fields of industry, commerce, agriculture, communication, household appliances and public facilities from the military and aerospace fields, especially in remote areas, mountainous areas, deserts, islands and rural areas, in order to save expensive transmission lines. However, at present, its cost is still very high, and tens of thousands of dollars are needed to generate 1kW power, so its large-scale use is still limited economically.
However, in the long run, with the improvement of solar cell manufacturing technology and the invention of new photoelectric conversion devices, environmental protection and the huge demand for renewable and clean energy in various countries, solar cells will still be a feasible method to utilize solar radiation energy, which will open up broad prospects for human beings to use solar energy on a large scale in the future.
[Edit this paragraph] Classification of solar cells
According to the crystalline state, solar cells can be divided into two categories: crystalline thin film type and amorphous thin film type (hereinafter referred to as a-), while the former is divided into single crystal type and polymorphic type.
According to materials, it can be divided into silicon thin films, compound semiconductor thin films and organic thin films, and compound semiconductor thin films can be divided into amorphous (a-Si:H, a-Si:H:F, a-SixGel-x:H, etc. ), III V group (GaAs, InP, etc. ), group II VI (Cds system) and zinc phosphide (Zn 3 p 2).
According to the different materials used, solar cells can also be divided into: silicon solar cells, multicomponent compound thin film solar cells, polymer multilayer modified electrode solar cells, nanocrystalline solar cells, and organic solar cells, among which silicon solar cells are the most mature and dominant in application.
(1) silicon solar cell
Silicon solar cells are divided into monocrystalline silicon solar cells, polycrystalline silicon thin-film solar cells and amorphous silicon thin-film solar cells.
Monocrystalline silicon solar cells have the highest conversion efficiency and the most mature technology. The highest conversion efficiency in the laboratory is 24.7%, and the highest mass production is 15%. It is still dominant in large-scale application and industrial production, but the cost of monocrystalline silicon is high, so it is difficult to significantly reduce the cost. In order to save silicon materials, polycrystalline silicon thin films and amorphous silicon thin films have been developed as alternative products of monocrystalline silicon solar cells.
Compared with monocrystalline silicon, polycrystalline silicon thin-film solar cells have lower cost and higher efficiency than amorphous silicon thin-film solar cells. The highest conversion efficiency in laboratory is 18%, and the conversion efficiency in industrial scale production is 10%. Therefore, polycrystalline silicon thin film batteries will soon occupy a dominant position in the solar power generation market.
Amorphous silicon thin-film solar cells have the advantages of low cost, light weight, high conversion efficiency, convenience for mass production and great potential. However, due to the degradation effect of photoelectric efficiency caused by its materials, its stability is not high, which directly affects its practical application. If we can further solve the stability problem and improve the conversion rate, then amorphous silicon solar cells will undoubtedly be one of the main development products of solar cells.
(2) Multi-compound thin film solar cells
Multi-compound thin film solar cells are inorganic salts, mainly including gallium arsenide III-V compounds, cadmium sulfide, cadmium sulfide and copper indium selenium thin film cells.
Polycrystalline thin-film batteries of cadmium sulfide and cadmium telluride have higher efficiency than amorphous silicon thin-film solar cells, lower cost than monocrystalline silicon batteries, and are easy for mass production. However, because cadmium is highly toxic, it will cause serious pollution to the environment, so it is not the best substitute for crystalline silicon solar cells.
The conversion efficiency of gallium arsenide (GaAs) III-V compound battery can reach 28%. GaAs compound material has ideal optical band gap, high absorption efficiency, strong radiation resistance and is insensitive to heat, which is suitable for manufacturing high-efficiency single-junction batteries. However, the high price of GaAs material greatly limits the popularity of GaAs batteries.
Copper-indium-selenium thin film battery (CIS) is suitable for photoelectric conversion, and there is no photo-degradation problem, and the conversion efficiency is the same as that of polysilicon. It has the advantages of low price, good performance and simple process, and will become an important direction of solar cell development in the future. The only problem is the source of the materials. Because indium and selenium are relatively rare elements, the development of such batteries is bound to be limited.
(3) polymer multilayer modified electrode type solar cell
Replacing inorganic materials with organic polymers is a new research direction of solar cell manufacturing. Organic materials are of great significance to the large-scale utilization of solar energy and the provision of cheap electricity because of their good flexibility, easy manufacture, wide sources of materials and low cost. However, the research on the preparation of solar cells from organic materials has just begun, and it can not be compared with inorganic materials, especially silicon cells, in terms of service life and battery efficiency. Whether it can be developed into a product with practical significance needs further research and exploration.
(4) Nanocrystalline solar cells
Nano-titanium dioxide crystal chemical energy solar cell is newly developed, which has the advantages of low cost, simple process and stable performance. Its photoelectric efficiency is stable above 10%, its manufacturing cost is only1/5 ~1/and its service life can reach more than 20 years.
However, since the research and development of this battery has just started, it is estimated that it will gradually enter the market in the near future.
(5) ? organic solar cell
As the name implies, organic solar cells are solar cells with organic materials as the core. Everyone is not familiar with organic solar cells, which makes sense. Today, more than 95% of mass-produced solar cells are silicon-based, and the remaining less than 5% are made of other inorganic materials.
[Edit this paragraph] Production process of solar cells (components)
Assembly line is also called packaging line, and packaging is a key step in solar cell production. Without a good packaging process, no matter how good the battery is, it will not produce a good assembly board. The packaging of the battery can not only ensure the battery life, but also enhance the battery resistance. High quality and long service life of products are the key to win customer satisfaction, so the packaging quality of component boards is very important.
Process:
1, battery inspection -2, front welding-inspection -3, back series-inspection -4, laying (glass cleaning, cutting, glass pretreatment, laying) -5, laminating -6, deburring (trimming and cleaning) -7, framing (gluing, corner pieces, etc.).
How to ensure the high efficiency and long life of components;
1, high conversion efficiency, high quality battery;
2. High-quality raw materials, such as EVA with high crosslinking degree, encapsulant with high adhesive strength (neutral silicone rubber), toughened glass with high light transmittance and high strength, etc.
3. Reasonable packaging technology
4. The rigorous work style of employees;
Because solar cells belong to high-tech products, some details in the production process, such as wearing gloves without gloves, uneven application of reagents, graffiti and other inconspicuous problems, are the enemies that affect the quality of products. Therefore, in addition to formulating reasonable production technology, it is very important for employees to be serious and rigorous.
Brief introduction of solar cell assembly process;
Brief introduction of technology: here is just a brief introduction of the function of technology to give you a perceptual understanding.
1. battery test: due to the randomness of battery chip manufacturing conditions, the produced batteries have different performances, so in order to effectively combine batteries with the same or similar performances, they should be classified according to their performance parameters; Battery testing is to classify batteries by testing their output parameters (current and voltage). In order to improve the utilization rate of batteries, qualified battery components are manufactured.
2. Front welding: The bus bar is welded on the main grid line of the front (negative electrode) of the battery. The bus bar is tinned copper strip, and the welding machine we use can spot weld the welding strip on the main grid line in the form of multiple points. The welding heat source is an infrared lamp (using the thermal effect of infrared rays). The length of the welding strip is about twice the length of the battery side. The additional welding tape is connected with the back electrode of the back battery piece during back welding.
3. Back-side series connection: Back-side welding is to connect 36 batteries in series into an assembly string. At present, the technology we use is manual. The positioning of the battery mainly depends on a membrane plate with 36 grooves to place the battery. The size of the groove corresponds to the size of the battery. The position of the groove has been designed. Different templates are used for components with different specifications. The operator uses an electric soldering iron and a solder wire to weld the front electrode (negative electrode) of the "front battery".
4. Laminating and laying: After connecting the back in series and passing the inspection, lay the component string, glass, cut EVA, glass fiber and back plate according to a certain level to prepare for lamination. Glass is pre-coated with a layer of primer to increase the bonding strength between glass and EVA. When laying, ensure the relative position of battery string and glass and other materials, and adjust the distance between batteries to lay a good foundation for lamination. (Laying level: from bottom to top: glass, EVA, battery, EVA, glass fiber, backboard).
5. Module lamination: put the placed battery into a laminator, pump out the air in the module by vacuumizing, and then heat and melt EVA to bond the battery, glass and back plate together; Finally, cool that extracted component. The lamination process is a key step in module production, and the lamination temperature and time are determined according to the properties of EVA. When we use fast curing EVA, the lamination cycle time is about 25 minutes. The curing temperature is 65438 050℃.
6. Trimming: EVA will extend outward during bonding and solidify under pressure to form burrs, which should be cut off after bonding.
7, framing: similar to putting a frame on the glass; The aluminum frame is installed on the glass module to increase the strength of the module, further seal the battery module and prolong the service life of the battery. The gap between the frame and the glass assembly is filled with silicone. Frames are connected by corner keys.
8. Welding junction box: Weld a box at the lead on the back of the assembly to facilitate the connection of the battery with other equipment or batteries.
9. high voltage test: high voltage test refers to applying a certain voltage between the frame of the module and the electrode leads to test the withstand voltage and insulation strength of the module to ensure that the module will not be damaged under harsh natural conditions (lightning strike, etc.). ).
10. Component test: The purpose of the test is to calibrate the output power of the battery, test its output characteristics, and determine the quality level of the component.
Design steps of solar cell array 1. Calculate the 24-hour consumption capacity p of the load.
P=H/V
V- rated power supply of load
2. Choose the sunshine time T(H) every day.
3. Calculate the working current of the solar array.
IP=P( 1+Q)/T
Q—— According to the surplus coefficient in rainy season, q = 0.2 1 ~ 1.00.
4. Determine the battery floating charge voltage VF.
The floating voltages of Ni-Cd (GN) and lead-acid (CS) batteries are 1.4 ~ 1.6V and 2.2V respectively.
5. Solar cell temperature compensation voltage.
VT=2. 1/430(T-25)VF
6. Calculate the working voltage VP of the solar cell array.
VP=VF+VD+VT
Where VD = 0.5 ~ 0.7
Approximately equal to VF
7. What is the output power WP of the solar array? Flat solar panels.
WP=IP×UP
8. According to the combination series table of VP and WP in the silicon panel, determine the number of series blocks and parallel groups of standard specifications.
Solar cell module refers to a part of solar cells, here mainly refers to photovoltaic panels for power generation.