The solar industry is moving from the research stage into the production stage, aiming at lower costs and maximised yields. As manufacturers of solar cells and modules face the pressure to drive down costs, they are turning to higher volume automated manufacturing, accompanied by high speed inspection to increase yields and improve the quality of their products.
By Srabani Sen & Sandhya Malhotra
Friday, January 15, 2010: There are four main parts of the manufacturing process, which occur in the following sequence—casting and wafering solar cell manufacturing; module assembly; solar system assembly and installation.
Solar cell plants are complex and large. In cell manufacturing, wafers typically undergo a process sequence of etching, diffusion and screen printing before they are tested and graded for incorporation into modules. For thin films, glass or stainless steel substrates are processed through steps of transparent conducting oxide deposition, semiconductor layer growth, laser scribing and metallisation. Thin film plants are designed to handle large substrates in sheet or roll form, so the process equipment is much larger than the wafer based plants.
Solar module assembly usually involves soldering of cells together to produce a cell string and laminating it between toughened glass on the top and a polymeric backing sheet at the bottom. It is then mounted on frames.
The leading players
All these production processes require solar manufacturing equipment—while some are fully automatic and semi-automatic machines, some processes can be done manually as well. Presently, India has nine cell manufacturers and 31-35 module manufacturers. The demand for production line is still less in India. While most of these machines are imported, particularly the fully automatic ones, there are few manufacturers and some turnkey solution providers as well.
Flexi Manufacturing Solutions Pvt Ltd designs and manufactures machines for the module manufacturing area. “We have exclusive range of products designed specially for the solar industry. The products range covers solar cell handling to complete panel handling,” explains R Kathirvel, director, Flexi Manufacturing Solutions Pvt Ltd. “For solar module making, we provide machines like tabbing station, stringing station, soldering stations, inspection station, solar module conveyers, IR scanning tables, height adjustable soldering inspection tables, pick and place systems, etc,” he adds.
DD Berg Project Consultants Pvt Ltd of Bergen Group provides turnkey solutions that include research and development, designing, planning and construction of technologically advanced production plants. “We have successfully executed major PV projects including the Moser Baer PV facility. Two of our similar projects under execution are Phoenix Solar and Ajit Solar. We have recently signed joint ventures with 3S (Swiss Solar Systems) and Schmid to represent them in India,” says Poonam Poonia, manager, Bergen Electronics Ltd.
Mumbai based Solar Machines Pvt Ltd is also a manufacturer of automatic and semi-automatic screen printing machines. “We offer a complete range of high quality silk-screen printing equipment for the screen printing industry. We have about 400 machines working successfully in India and have also exported to Sri Lanka, Bangladesh, Nepal, Middle East, African countries, Malaysia, etc,” informs its spokesperson.
Innovation according to needs
Solar cell and module manufacturers are under pressure to drive down costs in order to achieve grid parity. Also, with technology advancing at a fast pace, solar machines are being upgraded to meet high quality, high volume production, yet cost-effective capabilities of the solar industry. “If we want to significantly reduce the cost of production to achieve grid parity, we must not only improve the machines’ efficiency but also innovate new designs for these production lines,” explains Ajay Prakash Shrivastava, president, Maharishi Solar Technology Pvt Ltd. Points out Sunil Goel, its vice president, “Although the technology is 15 years old, improvement has taken place in the form of designs. There is a major shift from semi-automation to fully automation.”
Cost of setting up plants
The capital cost of translating solar cell into a laminated solar module is low, and smaller capacity plants can serve this purpose. But manufacturing solar cell is expensive which requires fully automatic production line. “The cost varies depending on the volume and productivity level as well as the scale of operation. While some manufacturing can be done from a home based plant, on the other hand, the set up of a higher capacity line can cost hundreds of millions of rupees,” says Kathirvel.
Goel, however, says that the cost of installation of a production line for solar modules with a combination of semi-automatic and fully-automatic machines is about Rs 5 crore. Maharishi Solar Technology has a vertically integrated manufacturing facility at Srikalahasti, Andhra Pradesh, to produce multi-crystalline silicon ingots, multi-crystalline wafers, multi/mono solar cells, SPV modules and SPV systems. “The plant was set up at a cost of Rs 50 crore,” informs Shrivastava.
Explains Shanker Grover, senior engineer, D D Berg, “Depending on the capacity, a fully automatic plant can cost more than Rs 150 crore. But with more players venturing into the solar domain, the cost of machines will get reduced as the demand will be more. Moreover, these machines have a life span of 25 years.” Uday Dharia, vice president, WAAREE Energies Pvt Ltd, which uses PV modules assembly line from P Energy of Italy, feels these robust production lines are economical.
However, Shrivastva suggests that before investing on such expensive machines one needs to take the guidance of a consultant and do some extensive research to get a competitive price. “We did extensive research and visited various machine manufacturers prior to deciding our equipment supplier,” says Dharia.
Financing is a challenge
If you are ready to set up a solar plant, you need to finance the machines as they are very expensive. Finding companies that specialise in financing solar machines can be tricky but not impossible. There are turnkey providers like DD Berg who can help. The most popular way of acquiring a machine, however, is through a lease. Banks also provide loans as Maharishi Solar acquired a loan from Exim Bank, although the processing of the loan took 18 months. Indian Renewable Energy Development Area (IREDA) under the Ministry of New and Renewable Energy (MNRE) extends loan on soft terms through designated intermediaries.
Maintenance is hassle free
As any other machine, solar machine also requires regular preventive activities. “These machines have components that are found in any other machine, hence no special attention is required,” says Kathirvel. Goel agrees, “The machines need proper oiling, general cleaning and routine checkup. All spare parts are available locally.” According to Shrivastava, “Bigger the solar plant, lesser will be the maintenance cost—which is usually 1 per cent of the equipment cost. But Grover feels that since these machines are complicated and deal with chemicals and gases, one needs to take preventive actions against leakages. The manufacturers of these machines usually provide free maintenance during the warranty period and thereafter under AMC. They also send engineers at the site for any repair.
“We get full support from our suppliers. We also have trained manpower to take care of the equipment indigenously,” says Dharia.
Key machines for solar cell line
To manufacture solar cells, the crystalline silicon wafer is used as the base substrate. After cleaning and texturing the surface, emitter is formed through a diffusion process. The front and back sides of the wafer are then isolated using the plasma etching technique; the oxide formed during the diffusion process is removed and, thus, an electrical field is formed. An anti-reflective coating is then applied to the surface of the cell using plasma enhanced chemical vapours to enhance the absorption of sunlight. The front and back sides of the cell are screen printed with metallic inks and the cell then undergoes a fire treatment in order to preserve its mechanical and electrical properties. Finally, the cell is tested and classified according to its parameters.
To understand about different types of machines used in the manufacturing of solar cells, we talked to Gurgaon based DD Berg, who entered into solar business in 2007 and provides turnkey solutions for solar production. Maharishi Solar Technology also has a fully automatic solar plant in Srikalahasti to manufacture cells. The company has imported machines from Germany, USA, Japan and Switzerland.
Acid texturing:
It uses hydrofluoric and nitric acids to clean and remove impurities caused by wire sawing, and textures the chemical surface to increase cell efficiency by reducing reflections. It is suitable for all standard wafer sizes and guarantees damage-free transport of the wafers through various processes.
Diffusion machine:
Silicon wafers are doped with small amounts of phosphorous to create the n-junction of the solar cell. This process is accomplished by depositing phosphorous vapour or coating on top of a silicon substrate. It is then fired at temperatures between 800°C and 1000°C to drive the phosphorous into the silicon, thus, creating the n-junction.
Etching: It is used for removing and cleaning diffused chemicals.
PECVD:
It gives blue imprint on the cell and an anti-reflection coating to store maximum amount of sunlight in a cell.
Metallisation/screen printing: Used for giving busbar, fingers and putting paste at the back of solar cells. It consists of mainly three printing processes AG, AG+AL and AL
Firing furnace:
This is the most critical step. The solar cells are rapidly heated to temperatures ranging from 780°C to 900°C followed by rapid cooling. It involves the process by which thick film conductive inks (usually silver and aluminum) are applied to the front and back of the solar cells.
Cell sorter:
At the end of the production process, the solar cells are sorted according to the effectiveness and optical criteria. A variety of different measurement and inspection procedures are used for this. The results allow each cell to be assigned a specific performance level and quality category.
Key machines for module assemble line
A PV module or panel is a packaged interconnected assembly of PV cells, also known as solar cells. The majority of modules use wafer based crystalline silicon cells or thin film cells based on silicon. The module, commonly called solar panel, is then used as a component in a larger PV system to generate electricity for commercial and residential applications.
But, have you ever wondered how these modules are manufactured? What machines are being used or what type of manpower is required to produce these modules? To have a first-hand look at the complete module line, we visited the Noida unit of Maharishi Solar Technology. Set up in September 2008, the PV plant has a total production area of 10,000 sq ft and manufactures modules ranging from 2-225 watts. “Presently, our’s is a small plant with a capacity of 2 MW but very soon we will increase it to 50 MW. We can manufacture 500 modules per day and plan to increase it to 1,000 modules. Our modules are supplied to mega power plants, government nodal agencies, hotels, hostels, hospitals, institutes and project developers,” says Sunil Goel, vice president, Maharishi Solar Technology Pvt Ltd.
Tabbing and stringing machine:
This machine interconnects solar cells by soldering flat metal leads or tabs to cell contacts. Solar cells are processed at a throughput of up to 600 cells per hour with high yield. The machine unloads solar cells from stacks and aligns their edges. Tab material is fed from spools, coated with flux, cut to length and provided with a stress-relief bend.
Fully automatic Lay up station:
It is a convenient system that allows the operator to cut materials, such as ethylene vinyl acetate (EVA) sheets and module backsheets to proper length. The rack holds rolls and a roller knife accurately cuts the materials.
Manual Lay up Station
can also be done manually by covering stringing cells with EVA sheets to protect the cells from physical stress. It is then enclosed in an aluminum frame with a glass front and normally with a material called TPT.
Electrical cell tester:
It tests the electrical performance of PV cells under simulated sunlight. The tester measures current voltage characteristics of cells at sun intensity. It also permits testing of very small area devices. A calibrated monitor cell is located on the test plane to monitor the light intensity.
Vacuum laminator:
This fully automatic machine laminates PV modules. The heart of the system is the laminator. It comprises two vacuum chambers which are separated by a flexible membrane. The chambers can be separately evacuated and ventilated. The laminator is equipped with a pin-lift system to lift the laminates above the heating plate. After lamination, the laminates are cooled down under defined pressure in a cooling press.
Curing machine: After lamination curing is done at high temperature.
Framing machine:
It frames at the four sides of the connected solar cells to provide better mounting options during the actual application.
Sun simulator:
This testing system features light sources that closely match the solar spectrum while avoiding the excessive solar cell heating. Sun simulators can test crystalline or thin film modules and can be integrated into a fully automated module production line or operated in manual mode.
SOLAR THERMAL PLANT: FLAT PLATE COLLECTOR LINE
Solar thermal energy is a technology for harnessing the solar energy into thermal energy (heat). This heat can be used water and space heating, solar process heating for industrial applications, solar drying, solar refrigeration and air conditioning, solar cooking, solar passive architecture, solar water desalination and water purification, etc.
The heart of a solar thermal system is a solar collector. its main function is to collect solar thermal energy and transfer it to the fluid to be heated. There are four different types of solar collectors including flat plate collector, evacuated tube collector, compound parabolic concentrator and parabolic trough concentrator.
solar collectors for domestic and industrial hot water application. “Besides manufacturing collectors, we have tied up with the US-based Abengoa Solar Inc (ASI) for production of solar energy, which would be used for industrial processing applications, air-conditioning, hot water needs and other thermal applications,” explains S K Kaila, vice president, Maharishi Solar Technology.
Power Press machine:
It gives ‘U’ shape slot/channel and punches to each aluminium frame.
Frame fixture:
It connects the four different aluminium frames’ channel on the fixture.
TIG Welding:
It welds the aluminium frames to give them high degree of thermal efficiency and 100 per cent bond conductance.
Chop saw machine:
It cuts welded channels up to 45 degree angle and also chops copper tubes.
Drill machine:
It drills choped copper tubes up to 13mm diameter.
Assembly of collector frame:
It assembles aluminium channel, angle, toughened glass, aluminium sheet and other components together.
Flange bridging fixture:
It makes absorber panel by putting a variety of materials like selective coated fin and tubes, copper tubes or riser and rock wool insulation, parallely to maximise solar efficiency and prevent degradation of the panel.
Hydraulic machine:
This is the last stage, where the machine checks and bridges any leakages in the absorber panel.
The solar industry is moving from the research stage into the production stage, aiming at lower costs and maximised yields. As manufacturers of solar cells and modules face the pressure to drive down costs, they are turning to higher volume automated manufacturing, accompanied by high speed inspection to increase yields and improve the quality of their products.
There are four main parts of the manufacturing process, which occur in the following sequence—casting and wafering solar cell manufacturing; module assembly; solar system assembly and installation.
Solar cell plants are complex and large. In cell manufacturing, wafers typically undergo a process sequence of etching, diffusion and screen printing before they are tested and graded for incorporation into modules. For thin films, glass or stainless steel substrates are processed through steps of transparent conducting oxide deposition, semiconductor layer growth, laser scribing and metallisation. Thin film plants are designed to handle large substrates in sheet or roll form, so the process equipment is much larger than the wafer based plants.
Solar module assembly usually involves soldering of cells together to produce a cell string and laminating it between toughened glass on the top and a polymeric backing sheet at the bottom. It is then mounted on frames.
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