Sunlight shines on the semiconductor p-n junction, forming new hole-electron pairs, in the p-n junction under the action of the electric field, holes from the n area flow to the p area, electrons from the p area flow to the n area, connecting the circuit to form an electric current. This is the working principle of photoelectric effect solar cell.
I. Solar Power Generation MethodsThere are two ways of generating solar power, one is the photo-thermal-electric conversion method, and the other is the direct conversion method of photoelectricity.
(1) The photo-thermal-electric conversion method generates electricity by utilizing the thermal energy produced by solar radiation, generally by solar collectors to convert the absorbed thermal energy into the steam of the work material, and then drive the turbine to generate electricity. The former process is the light - heat conversion process; the latter process is the heat - electricity conversion process, as with ordinary thermal power generation. The disadvantage of solar thermal power generation is that the efficiency is very low and the cost is very high, it is estimated that its investment is at least 5 to 10 times more expensive than ordinary thermal power plants. A 1000MW solar thermal power plant requires an investment of 2 to 2.5 billion dollars, with an average investment of 2,000 to 2,500 dollars for 1kW. Therefore, it can only be used on a small scale for special occasions at present, while large-scale utilization is economically uneconomical and cannot yet compete with ordinary thermal or nuclear power plants.
(2) light - direct conversion of electricity the way the way is to use the photoelectric effect, the sun's radiant energy is directly converted into electrical energy, light - the basic device is the conversion of solar cells. Solar cell is a device that directly converts the sun's light energy into electrical energy due to the photovoltaic effect, is a semiconductor photodiode, when the sun shines on the photodiode, the photodiode will turn the sun's light energy into electrical energy, generating an electric current. When many cells are connected in series or parallel can become a relatively large output power of the solar cell array. Solar cells are a promising new type of power source with three major advantages: permanence, cleanliness and flexibility. Solar cells have a long life, as long as the sun exists, solar cells can be an investment and long-term use; compared with thermal power, nuclear power generation, solar cells do not cause environmental pollution; solar cells can be large and small and large, large to millions of kilowatts of medium-sized power stations, small to just for a household with a solar panel, which is incomparable to other power
The current situation of the solar battery industry
At this stage, the photoelectric effect of thin-film solar cells work as the mainstream, while the photochemical effect of the work of wet solar cells is still in its infancy.
Global solar cell industry status
According to Dataquest's statistics, at present, the world*** has 136 countries into the popularization of the application of solar cells in the boom, of which 95 countries are in large-scale research and development of solar cells, and actively produce a variety of related energy-saving new products. 1998, the world's production of In 1998, the world's production of solar cells, its total power generation amounted to 1,000 megawatts in 1999 amounted to 2,850 megawatts. 2000, the world's nearly 4,600 manufacturers to provide the market with photovoltaic cells and photovoltaic cells as a power source of the product.
At present, many countries are formulating medium- and long-term solar energy development plans to prepare for the large-scale development of solar energy in the 21st century, the U.S. Department of Energy launched the National Photovoltaic Program (NPV), and Japan launched the Sunshine Initiative (SIP). system performance and engineering, and PV applications and market development in five areas of research.
The U.S. has also launched a "solar streetlight program" aimed at making streetlights in some U.S. cities solar-powered, with each streetlight saving 800 degrees of electricity per year, according to the program. Japan is also implementing solar energy "70,000 sets of project plan", Japan is ready to popularize the solar energy residential power generation system, mainly installed on the roof of the home of the solar cell power generation equipment, the family with the remaining electricity can also be sold to the power company. A standard household can install a system that generates 3,000 watts of electricity. Europe will be the research and development of solar cells in the famous "Eureka" high-tech program, launched the "100,000 sets of engineering programs." These popularization of the application of photovoltaic cells as the main content of the "solar energy project" program is currently promoting the solar photovoltaic cell industry, one of the important driving forces of the development.
Japan, South Korea and the European region, the total **** 8 countries recently decided to work together, inland Asia and the African desert region to build the world's largest solar power station, their goal is to account for about 1/4 of the global land area of the desert area of the long hours of sunshine resources effectively utilized for 300,000 users to provide 1 million kilowatts of electricity. The plan will begin in 2001 and take four years to complete.
Currently, the U.S. and Japan hold the largest market shares in the world photovoltaic market. The United States has the world's largest photovoltaic power plant, its power for 7MW, Japan has also built a power generation power of 1MW photovoltaic power plant. There are 230,000 photovoltaic power plants in the world, with Israel, Australia and New Zealand leading the way.
Since the 1990s, the global solar cell industry has continued to grow at an annual rate of 15%. According to Dataquest released the latest statistics and forecasts show that the United States, Japan and Western European industrialized countries in the research and development of solar energy in the total investment in 1998 amounted to 57 billion U.S. dollars; in 1999, 64.6 billion U.S. dollars; in 2000, 70 billion U.S. dollars; in 2001, it will be 82 billion U.S. dollars; 2002 is expected to break through the 100 billion U.S. dollars.
China's solar cell industry status
China attaches great importance to the research and development of solar cells, as early as during the 7th Five-Year Plan period, amorphous silicon semiconductor research has been included in the major national issues; the 8th Five-Year Plan and the 9th Five-Year Plan period, China's research and development focus on large-area solar cells, etc. In October 2003, the National Development and Reform Commission (NDRC), the Ministry of Science and Technology (MOST) to develop a plan for solar resource development for the next five years, the NDRC and the MOST to develop a plan for solar resource development for the next five years. In October 2003, the National Development and Reform Commission and the Ministry of Science and Technology formulated a plan for the development of solar energy resources in the next five years, the Development and Reform Commission, "Brightness Project" will raise 10 billion yuan for the promotion of solar power generation technology, the plan is to 2005, the country's total installed capacity of solar power generation system to reach 300 megawatts.
In 2002, the relevant state ministries and commissions launched the "western provinces and districts without electricity township electricity program", through solar energy and small wind power to solve the problem of electricity in the western seven provinces and districts without electricity townships. The launch of this project has greatly stimulated the solar power industry, the domestic construction of several solar cell packaging line, so that the annual production of solar cells increased rapidly. China currently has 10 solar cell production lines, the annual production capacity of about 4.5MW, of which 8 production lines were introduced from abroad, in these 8 production lines, there are 6 monocrystalline silicon solar cell production line, 2 amorphous silicon solar cell production line. According to expert forecasts, China's photovoltaic market demand for 5MW per year, 2001 to 2010, the annual demand will reach 10MW, from 2011, China's photovoltaic market demand will be greater than 20MW.
Currently, the domestic solar energy silicon production enterprises are mainly monocrystalline silicon plant in Luoyang, Hebei, Ningjin, monocrystalline silicon base and Emei Semiconductor Materials Factory in Sichuan and other manufacturers, of which Hebei, Ningjin, monocrystalline silicon base is the world's largest solar cell production line, the production of monocrystalline silicon production lines. Ningjin monocrystalline silicon base is the world's largest solar monocrystalline silicon production base, accounting for about 25% of the world solar monocrystalline silicon market share.
In the downstream market of solar cell materials, the current domestic production of solar cells, mainly Baoding Yingli New Energy, Wuxi Suntech, Kaifeng Solar Cells Factory, Yunnan Semiconductor Device Factory, Qinhuangdao Huamei PV Electronics, Zhejiang Zhongyi Solar Energy, Ningbo Solar Power, Kyocera (Tianjin) Solar Energy, etc., with a total annual production capacity of more than 120MW.
Solar cells and solar power prospect analysis
At present, the application of solar cells from the military field, the aerospace field into the industrial, commercial, agricultural, communications, household appliances, and utilities, etc., especially can be decentralized in remote areas, mountains, deserts, islands and rural areas in order to save the cost of very expensive transmission lines. But at the present stage, its cost is still very high, send out 1kW of electricity need to invest tens of thousands of dollars, so the large-scale use is still subject to economic constraints.
But in the long run, with the improvement of solar cell manufacturing technology and the invention of new light - electricity conversion device, the protection of the environment and the huge demand for renewable clean energy, solar cells will still be the use of solar radiation energy is a more practical and feasible way to use the sun's radiation can be used for the future of mankind's large-scale use of solar energy to open up a wide range of prospects.
Classification of solar cells
Solar cells can be divided into two categories: crystalline thin film and amorphous thin film (hereinafter referred to as a-) according to the state of crystallization, which is divided into mono-crystalline and polycrystalline.
By material can be divided into silicon thin film form, compound semiconductor thin film form and organic film form, and compound semiconductor thin film form is divided into amorphous form (a-Si:H, a-Si:H:F, a-SixGel-x:H, etc.), Ⅲ V (GaAs, InP, etc.), Ⅱ Ⅵ (Cds system) and zinc phosphide (Zn 3 p 2 ) and so on.
Solar cells according to the different materials used, solar cells can also be divided into: silicon solar cells, polymer compounds thin film solar cells, polymer multilayer modified electrode type solar cells, nanocrystalline solar cells four categories, of which silicon solar cells are currently the most mature development, in the application of the dominant position.
(1) Silicon solar cells
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 23%, and the efficiency in large-scale production is 15%. In large-scale applications and industrial production still occupy a dominant position, but due to the high cost of monocrystalline silicon, significantly reduce its cost is very difficult, in order to save silicon materials, the development of polycrystalline silicon thin film and amorphous silicon thin film for monocrystalline silicon solar cells as an alternative product.
Polycrystalline silicon thin film solar cells and monocrystalline silicon comparison, low cost, and efficiency is higher than amorphous silicon thin film batteries, the highest conversion efficiency of its laboratory 18%, industrial-scale production of conversion efficiency of 10%. Therefore, polycrystalline silicon thin-film batteries will soon dominate the solar power market.
Amorphous silicon thin-film solar cells are low-cost and lightweight, with high conversion efficiencies, facilitating large-scale production, and have great potential. But subject to its material-induced photoelectric efficiency decline effect, stability is not high, directly affecting its practical applications. If we can further solve the stability problem and improve the conversion rate problem, then, amorphous silicon large solar cells is undoubtedly one of the main development of solar cells.
(2) multi-compound thin-film solar cells
Multi-compound thin-film solar cell materials for inorganic salts, including gallium arsenide III-V compounds, cadmium sulfide, cadmium sulfide, and copper selenium thin-film batteries.
Cadmium sulfide, cadmium telluride polycrystalline thin-film battery efficiency than amorphous silicon thin-film solar cell efficiency, lower cost than monocrystalline silicon batteries, and is also easy to large-scale production, but due to the cadmium has a high degree of toxicity, will cause serious pollution of the environment, so it is not the most ideal alternative to the crystalline silicon solar cells.
Gallium arsenide (GaAs) III-V compound battery conversion efficiency of up to 28%, GaAs compound material has a very ideal optical band gap and high absorption efficiency, anti-irradiation ability, heat insensitive, suitable for the manufacture of high-efficiency monojunction battery. However, the price of GaAs materials is not expensive, thus limiting the popularity of GaAs batteries to a large extent.
Copper indium selenide thin-film batteries (CIS) are suitable for photovoltaic conversion, there is no photoelectric degradation, and the conversion efficiency is the same as that of polycrystalline silicon. With the advantages of low price, good performance and process simplicity, it will become an important direction for the development of solar cells in the future. The only problem is the source of materials, due to indium and selenium are relatively rare elements, so the development of such batteries is bound to be limited again.
(3) Polymer multilayer modified electrode-type solar cells
Replacing inorganic materials with organic polymers is just beginning a research direction in solar cell manufacturing. Due to the advantages of organic materials such as good flexibility, easy fabrication, wide range of material sources, and bottom cost, thus it is important for the large-scale utilization of solar energy to provide cheap electricity. However, the study of organic materials to prepare solar cells has only just begun, whether it is the service life, or battery efficiency can not be compared with inorganic materials, especially silicon cells. Whether it can be developed into a practical significance of the product, but also to be further research and exploration.
(4) nanocrystalline solar cells
Nanometer TiO2 crystal chemical energy solar cells are newly developed, the advantage lies in its cheap cost and simple process and stable performance. Its photovoltaic efficiency is stable at more than 10%, the production cost is only 1/5 ~ 1/10 of the silicon solar cells. life expectancy can reach more than 2O years.
But because the research and development of such batteries has just begun, it is estimated that in the near future will gradually on the market.
Solar cell (module) production process
Component line, also known as the encapsulation line, encapsulation is a key step in the production of solar cells, there is no good encapsulation process, how good the battery is also unable to produce good component panels. The encapsulation of the battery not only ensures the life of the battery, but also enhances the impact strength of the battery. The high quality and life span of the product is the key to win can customer satisfaction, so the encapsulation quality of the component board is very important.
Process:
1, battery inspection - 2, front side welding - inspection - 3, back side stringing - inspection - 4, laying (glass cleaning, material Cutting, glass pretreatment, laying) --5, lamination --6, de-burr (de-burr, cleaning) --7, mounting frame (glue, mounting corner key, punching, mounting frame, scrubbing residual glue) --8, welding junction box - 9, high-voltage test - 10, component testing - appearance inspection - 11
How to ensure high efficiency and high life of the module:
1, high conversion efficiency, high quality cells;
2, high-quality raw materials, such as: high cross-linking degree of EVA, high bonding strength of encapsulant (neutral silicone resin glue), high transmittance, high strength toughened glass, etc.;
3, a reasonable encapsulation process
4, the staff's rigorous work style;
Because the solar cell is a high-tech products, the production process of some of the details of the problem, some inconspicuous issues such as should be wearing gloves and do not wear, should be uniformly coated with reagents and scribbling to finish the job, etc. is the enemy of product quality, so in addition to the development of a reasonable production process, the staff's conscientiousness and rigor is very important.
Introduction of solar cell assembly process:
Introduction of the process: Here is only a brief introduction to the role of the process, to give you a perceptual understanding.
1, battery testing: due to the randomness of the battery cell production conditions, the production of battery performance is not the same, so in order to effectively combine the performance of the same or similar batteries, so it should be classified according to its performance parameters; battery testing that is, through the testing of the size of the battery's output parameters (current and voltage) for its classification. In order to improve the utilization rate of the battery, to make the quality of qualified battery components.
2, Positive welding: is to weld the converging strip to the front of the battery (negative) on the main grid line, the converging strip is tinned copper tape, we use the welding machine can be welded in the form of multi-point welding strip on the main grid line. The heat source for welding is an infrared lamp (utilizing the thermal effect of infrared rays). The length of the strip is approximately twice the length of the battery side. Extra welding tape in the back welding with the back of the battery cells behind the back electrode connected
3, the back of the string: the back welding is the 36 pieces of cells in series to form a component string, we are currently using the process is manual, the positioning of the battery mainly rely on a film with a board, there are 36 placed in the cell groove, the size of the groove and the size of the battery corresponds to the groove position has been designed, different sizes of components using a template, and the location of the groove. Different sizes of components use different templates, the operator uses a soldering iron and soldering wire to solder the front electrode (negative) of the "front battery" to the back electrode (positive) of the "back battery", so that the 36 pieces of the string together and in the components of the string of The front electrode (negative electrode) is welded to the back electrode (positive electrode) of the "back battery".
4, laminating and laying: the back of the string is connected and passed the inspection, the component string, glass and cut EVA, glass fiber, backplane in accordance with a certain level of laying, ready to laminate. The glass is coated with a layer of reagent (primer) to increase the adhesive strength of the glass and EVA. Ensure that the relative position of the battery string and the glass and other materials when laying, adjust the distance between the batteries, to lay a good foundation for the lamination. (Laying level: from the bottom up: glass, EVA, battery, EVA, fiberglass, backplane).
5, component lamination: put the laid battery into the laminating machine, extract the air inside the component by vacuuming, and then heat to melt the EVA to bond the battery, glass and backplane together; finally cool down and take out the component. The lamination process is a critical step in the production of the module. The lamination temperature and time are determined by the nature of the EVA. When we use fast curing EVA, the lamination cycle time is about 25 minutes. The curing temperature is 150°C.
6, trimming: lamination of EVA melting due to the pressure and the extension of the curing outward to form a burr, so the lamination should be removed.
7, framing: similar to the glass to install a frame; to the glass component aluminum frame, increase the strength of the component, further sealing of the battery components, to extend the service life of the battery. The gap between the frame and the glass component is filled with silicone resin. Each bezel is connected to each other with an angle key.
8. Welding junction box: Weld a box on the back of the module at the lead wire to facilitate the connection between the battery and other equipment or batteries.
9, high-voltage test: high-voltage test means applying a certain voltage between the module frame and electrode leads to test the voltage resistance and insulation strength of the module to ensure that the module will not be damaged under adverse natural conditions (lightning strikes, etc.).
10, component testing: 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.