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Solar cell module

2021-08-17 09:13:05

According to the statistics of European Photovoltaic Industry Association (epla) in 2012, crystalline silicon solar cells have always accounted for the vast majority of the solar cell market and are the mainstream of photovoltaic power generation.

As the crystalline silicon solar cell itself is easy to be broken and corroded, if directly exposed to the atmosphere, the photoelectric conversion efficiency will decline due to the influence of humidity, dust, acid rain and other factors, and it is also easy to be damaged. Therefore, crystalline silicon solar cells must generally be made into a flat structure by means of glue sealing and lamination. For power supply, several single cells must be connected in series and parallel and tightly encapsulated, which is solar cell module.

Solar cell module 1

Solar cell module packaging is the key link for long-life utilization of solar cells, so as to isolate the contact channel between solar cells and the outside atmosphere, protect electrodes and avoid interconnection corrosion. In addition, packaging with rigid materials also avoids the fragmentation of solar cells. The packaging quality determines the performance and service life of crystalline silicon solar cell modules. The packaging of crystalline silicon solar cells mainly adopts vacuum hot pressing method. After the solar cells with positive and negative electrodes are welded in series and parallel to form a crystalline silicon solar cell array, EVA (ethylene / vinyl acetate) material is used on both sides, low iron tempered glass and TPT are added on both sides, and put into the vacuum laminator to vacuum and heat the lamination chamber, Glass / EVA / solar cell string / EVA / TPT are hot pressed together to ensure practicability, interchangeability, reliability and service life. TPT (tedler polyeast tedler) is the cover on the back of the solar cell, which is a white fluoroplastic film. After packaging, the components have sufficient mechanical strength to withstand conflicts, vibration and other stresses during transportation, installation and use, so as to reduce the overall power loss.

Packaging materials for solar cell modules

Component life is one of the important factors to measure component quality. The working life of components is closely related to packaging materials and packaging technology. Packaging materials play an important role in solar cells, such as glass, EVA, glass fiber and TPT. The materials, parts and structures used in the assembly are required to be consistent with each other in service life, so as to avoid the failure of the whole assembly due to one damage.

(1) Upper cover plate

The upper cover plate covers the front of the solar cell module and forms the outermost layer of the module. It should not only have high light transmittance, but also be firm and play the role of long-term battery protection. The materials used for the upper cover plate include: tempered glass, polyacrylic resin, fluorinated ethylene propylene, transparent polyester, polycarbonate, etc.

At present, the mainstream product of packaging glass used for solar cells is low iron tempered embossed glass. Within the wavelength range of spectral response of solar cells (320 ~ 1100nm), its iron content is very low (less than 0.015%), so its light transmittance is very high (about 91% within the spectral range of 400 ~ 1100m). It is white from its edge, so it is also called white glass, It has high reflectivity for infrared rays greater than 1200nm.

In addition, toughening the glass can not only maintain a high light transmittance, but also increase the strength of the glass to 3 ~ 4 times that of ordinary flat glass. The glass toughening process helps to improve the ability of solar cell module to resist hail and accidental attack, and ensure that the whole solar cell module has high enough mechanical strength. In order to reduce the reflection of light, some antireflection processes can be carried out on the glass surface to make "antireflection glass". The main measure is to coat a thin film layer on the glass surface to reduce the reflectivity of the glass.

(2) Resin

Resins include room temperature curing silicone rubber, fluorinated ethylene propylene, polyvinyl butyral, transparent dioxygen resin, polyvinyl acetate, etc. The general requirements are as follows: ① high light transmittance within the visible light range; ② Elastic; ③ Good electrical insulation performance; ④ It can be applied to automatic component packaging. Resin packaging is a simple form of solar cell packaging. It uses simple measures to package and protect solar cells, and the material cost is relatively low. With its flexibility and low price, it is widely used in small solar products, such as solar lawn lamps, solar chargers, solar teaching appliances, solar toys, solar road signs and solar signal lamps.

(3) Organic silica gel

The basic structural unit of silicone products is composed of silicone oxygen links, and the side chains are connected with other organic groups through silicon atoms. Silicone is not only resistant to high temperature, but also resistant to low temperature. It can be used in a wide temperature range. Both chemical properties and physical and mechanical properties change little with temperature. Silicone products have good electrical insulation properties. Their dielectric loss, voltage resistance, arc resistance, corona resistance, volume resistance coefficient and surface resistance coefficient are among the best among the insulating materials. Moreover, their electrical properties are little affected by temperature and frequency, and the silicone adhesive is colorless and highly transparent after curing.

(4) EVA adhesive film

EVA, also known as solar cell adhesive film, is used to bond glass and solar cell array, solar cell array and TPT film. Its light transmittance is good. Two layers of EVA adhesive film are generally added to the standard solar cell module. The EVA adhesive film plays a bonding role between the battery and glass, and between the battery and TPT. EVA is a copolymer of ethylene and vinyl acetate. Unmodified EVA has the characteristics of transparency, softness, hot-melt adhesion, low melting temperature and good melting fluidity. These characteristics meet the requirements of solar cell sealing, but they have poor heat resistance, easy extension and low elasticity, low cohesion strength, easy thermal shrinkage, resulting in solar cell fragmentation and bonding delamination. In addition, as a product used outdoors for a long time, whether EVA adhesive film can withstand outdoor ultraviolet aging and thermal aging is also a very important problem. EVA solar cell adhesive film is prepared by heating and extrusion with EVA as raw material and appropriate modifying additives, which is easy to cut at room temperature; The solar cell module is laminated and sealed according to the heating and curing conditions, and a permanent adhesive seal is generated after cooling. The glass fiber layer is woven with glass fiber to remove bubbles that may be sealed in the battery board during lamination.

(5) Back material

Generally, it is tempered glass, aluminum alloy, plexiglass, TPT, etc. TPT is used to prevent water vapor from entering the solar cell module and reflect sunlight. Because of its high infrared reflectivity, it can reduce the working temperature of the module and improve the efficiency of the module. The thickness of TPT film is 0.12mm, and the average reflectivity is 0.648 in the spectral range of 400 ~ 1100nm.

At present, TPT composite membrane is widely used, which has the following requirements: ① it has good weather resistance and can withstand outdoor temperature change, ultraviolet aging and thermal aging; ② No change in lamination temperature; ③ It is firmly combined with the bonding material.

(6) Border

Flat panel components must have frames to protect components, and components with frames form a square array. The frame is sealed to the edge of the component with adhesive. The main materials are stainless steel, aluminum alloy, rubber, reinforced plastic, etc.

Production process of solar cell module

(1) Battery test

Due to the randomness of battery production conditions, the produced batteries have different performance. Therefore, in order to effectively combine batteries with the same or similar performance, they should be classified according to their performance parameters; Battery test is to classify the battery by testing the output parameters (current and voltage) of the battery, so as to improve the utilization rate of the battery and make qualified battery components.

(2) Front welding

Front welding is to weld the bus strip to the main grid line of the front (negative) of the battery. The bus strip is tinned copper strip. The welding machine can spot weld the welding strip on the main grid line in the form of multiple points. The heat source for welding is an infrared lamp. The infrared thermal effect is used for welding. The length of the welding strip is about twice the side length of the battery. The excess welding strip is connected with the back electrode behind the battery during back welding.

(3) Back serial connection

The back serial connection is to connect the batteries in series to form a component string. The positioning of the battery mainly depends on a mold plate, which has a groove for placing the battery. The size of the groove corresponds to the size of the battery. The position of the groove has been designed, and different templates are used for components of different specifications. The operator uses an electric soldering iron and solder wire to weld the front electrode (negative electrode) of the "front battery" to the back electrode (positive electrode) of the "rear battery", so as to connect the battery pieces together in series and weld leads at the positive and negative electrodes of the assembly string.

(4) Laminated laying

After the back is connected in series and passed the inspection, the series connected battery sheet, glass and cut EVA, glass fiber and back plate shall be laid according to a certain level and prepared for lamination. The glass is coated with a layer of reagent in advance to increase the bonding strength between glass and EVA. During 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. The laying layers are glass, EVA, battery, EVA, glass fiber and backplane from bottom to top.

(5) Component lamination

Put the laid battery into the laminator, draw out the air in the module by vacuuming, and then heat to melt EVA to bond the battery, glass and back plate together; Finally, cool down and take out the components. Lamination process is a key step in component production. Lamination temperature and lamination time are determined according to the properties of EVA. At present, rapid curing EVA is mainly used. The lamination cycle time is about 25min and the curing temperature is 150 ℃.

(6) Trimming

During lamination, EVA melts and extends outward due to pressure to solidify to form burr, so it shall be cut off after lamination

(7) Frame

Similar to the glass frame, the glass module is equipped with aluminum alloy frame 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 component is filled with polysiloxane resin, and the frames are connected with angle keys.

(8) Welding junction box

Weld a box at the lead on the back of the module to facilitate the connection between the battery and other equipment or batteries. The solar junction box provides users with a combined connection scheme of solar cell allegro. It is a solar cell array composed of solar cell modules and a solar charging control device

The connector is a cross domain comprehensive design integrating electrical design, mechanical design and material science. It is an important component of solar modules.

Structure of junction box: general solar junction box includes upper cover and lower box. The upper cover is connected with the lower box through a rotating shaft, which is characterized in that several wiring bases are arranged in parallel in the lower box, and each adjacent two wiring bases are connected through one or more diodes. The upper cover or lower box is made of thermal conductive materials, and its product types now include: glue filled junction box, screen wall junction box, small component junction box, etc.

(9) 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 components. The parameters of solar cell module shall include insulation resistance, insulation strength, working temperature, reflectivity, thermomechanical stress and other parameters in addition to some common parameters that are the same as those of single solar cell. Insulation resistance measurement is to measure the insulation resistance between the output end of the component and the metal substrate or frame. Safety inspection shall be conducted before measurement. For the square array that has been installed and used, first check the ground potential, electrostatic effect, and whether the metal substrate, frame and support are well grounded. An ordinary megger can be used to measure the insulation resistance, but a megger with a voltage level roughly equivalent to the open circuit voltage of the square array to be measured shall be selected. When measuring the insulation resistance, the atmospheric relative humidity shall not be greater than 75%. Insulation strength is the ability of the insulation itself to withstand voltage. When the voltage acting on the insulation exceeds a certain critical value, the insulation will be damaged and lose its insulation function. Generally, the insulation strength of power equipment is expressed by breakdown voltage; The insulation strength of insulating materials is expressed by the average breakdown electric field strength, referred to as the breakdown electric field strength. Breakdown field strength refers to the voltage at which breakdown occurs divided by the distance between the two electrodes to which the voltage is applied under the specified test conditions.

In the case of indoor test and outdoor test, the requirements for the shape, size and size of the reference component are inconsistent. In the case of indoor test, the structure, material, shape, size, etc. of the reference component shall be the same as that of the component to be tested. When measuring in outdoor sunlight, the above requirements can be slightly relaxed, that is, reference components with small size and different shapes can be used. In the measurement of component parameters, it is better to calibrate the irradiance by using the reference component than directly using the standard solar cell.

The ground solar cell module operates in the outdoor environment for many years. It must be able to repeatedly withstand various harsh climatic conditions and other changeable environmental conditions, and ensure that its electrical performance does not deteriorate seriously within a fairly long rated life (usually more than 15 years). Before and after each item, it is necessary to observe and check whether the appearance of the component is abnormal and whether the decrease of the maximum output power is greater than 5%. Those with abnormal appearance or the decrease of the maximum output power is greater than 5% are unqualified, which is the common requirement of all tests.

High voltage test refers to applying a certain voltage between the component frame and the electrode lead to test the withstand voltage and insulation strength of the component, so as to ensure that the component will not be damaged under harsh natural conditions (such as lightning, etc.).

Vibration and impact test: the purpose of vibration and impact test is to assess its ability to withstand transportation. The vibration time is 20min in the normal direction and 20min in the tangential direction, and the impact times are 3 times in the normal direction and 3 times in the tangential direction

Hail test: the steel ball used in the simulated hail test weighs about 227g, and the falling height depends on the cover plate material of the module (tempered glass: height 100cm, high-quality glass: 50cm), falling towards the center of the solar cell module.

Salt spray test: solar cell modules used in offshore environment shall be subject to this test. After being stored in the fog of 5% sodium chloride aqueous solution for 96h, check the appearance, maximum output power and insulation resistance. More stringent inspections include ground sunlight irradiation test, torsion test, constant damp heat storage, low temperature storage and temperature alternating inspection, etc.

(10) Packaging warehousing

The solar cell modules can be packaged and put into storage after passing the acceptance.

With the development of amorphous silicon solar cells, the same super smooth surface packaging method as crystalline silicon solar cells is also being studied. The substrate glass of integrated solar cells is directly used as the protective plate of the light receiving surface, and the connection of each unit cell does not need wires, so the assembly process of components can become particularly simple.

According to the purpose, purpose and scale, solar cells are divided into various types of components:

① Components for electronic products. In order to drive electronic products such as calculators, watches, radios, televisions and chargers, a voltage of 1.5V to tens of volts is generally required. The voltage generated by a single solar cell is less than 1V, so in order to drive these electronic products, multiple solar cell elements must be connected in series to achieve the required voltage.

② Condenser assembly. Solar cell power generation system works under focused sunlight. It is divided into lens type and reflector type. The large-area convex lens necessary for focusing adopts a lens, which connects the divided convex lens surfaces. There are two forms of reflective type. One is to use paraboloid mirror, and the solar cell is placed on its focus. The other is to place solar cell on the bottom and configure reflector on the side; In addition to monocrystalline silicon solar cells, gallium arsenide solar cells with high conversion efficiency are often used. In addition, there is a fluorescent concentrating plate solar cell, which changes the absorbed solar cell light into fluorescence through the fluorescent plate. The fluorescence propagates in the fluorescent plate and is finally concentrated at the end of the solar cell.

③ Hybrid components. Photothermal hybrid module is a device for more effective use of solar energy and solar power generation and heating. The hybrid components include condensing type photothermal hybrid components, collector type photothermal hybrid components, etc.

Solar cell module production equipment

A complete set of equipment on the production line of solar cell modules: laser dicing machine (solar cell cutting, silicon wafer cutting), solar module laminating machine, solar module tester, solar cell sorting machine, etc. These equipment can be produced by domestic manufacturers.

(1) Laser dicing machine

Laser dicing machine equipment is mainly used for semiconductors such as solar cell, silicon, germanium and gallium arsenide

Engraving and cutting of bulk substrate materials. The laser dicing machine adopts computer-controlled semiconductor pump and lamp to pump laser

The workbench can do various movements according to the graphic track. Pump means excitation or excitation. Laser, also known as laser, has high brightness, high collimation and high coherence. It can be used in industrial processing, medical treatment, military and other fields.

Both semiconductor pumped and lamp pumped lasers use Nd: YAG (neodymium doped yttrium aluminum garnet) crystals

As the working material produced by laser, the absorption peak of this material to pump light is near 808 nm. Lamp pumping uses the light emitted by krypton lamp to pump Nd: YAG crystal to produce 1064nm working laser. However, the spectrum of the light emitted by krypton lamp is wide, but there is a slightly larger peak at 808nm, and the light of other wavelengths is finally converted into useless heat and dissipated.

There is also a semiconductor pump, which uses the 808nm laser emitted by the semiconductor laser diode to pump the Nd: YAG crystal to produce the laser. Because the emission wavelength of semiconductor laser diode is consistent with the absorption peak of laser working material, and the pump light mode can well match the laser oscillation mode, the optical conversion efficiency is very high. The optical conversion efficiency of the semiconductor pumped laser can reach more than 35% (the lamp pumping efficiency is only 3% ~ 6%), and the overall efficiency is one order of magnitude higher than that of the lamp pumped laser, so only a lightweight water cooling system is required. Therefore, the semiconductor pumped laser has the advantages of small volume, light weight and compact structure.

(2) Solar module laminator

The solar module laminating machine is used for packaging single crystal (polycrystalline) solar modules, and can automatically complete the processes of heating, vacuum pumping, lamination, etc. according to the setting program; The automatic mode is to preset the lamination control parameters through the console, automatically run after manually closing the cover, automatically alarm and open the cover after lamination, and wait for the next batch of components to be packaged; The manual mode is manual operation through the control button on the console. The flat lamination platform makes the battery board horizontally placed, evenly heated, high degree of automation and stable performance. One person can easily complete the operation of placing and taking out the battery board.

(3) Solar module tester

The solar module tester is specially used for the testing of solar monocrystalline silicon and polycrystalline silicon battery modules. By simulating the solar spectral light source, the relevant electrical parameters of the battery module are measured. Generally, it has a unique correction device, which inputs compensation parameters for automatic / manual temperature compensation and light intensity compensation, and has the functions of automatic temperature measurement and temperature correction.

Measuring the electrical performance of solar cells is attributed to measuring its volt ampere characteristics. Because the volt ampere characteristics are related to the test conditions, the measurement must be carried out under the uniformly specified standard test conditions, or the measurement results must be converted to the standard test conditions, so as to identify the good or bad of the electrical performance of solar cells. Standard test conditions include standard sunlight (standard spectrum and standard irradiance) and standard test temperature. The temperature can be controlled manually, and the standard sunlight can be simulated manually or found under natural conditions. Using simulated sunlight, the spectrum depends on the type of electric light source and the filter and reflection system; Irradiance can be calibrated with the calibration value of short-circuit current of standard solar cell. In order to reduce the spectral mismatch error, the spectrum of simulated sunlight should be as close as possible to the standard sunlight spectrum, or the standard solar cell with basically the same spectral response as the measured cell should be selected.

For the detection of solar cell efficiency, one case is that the spectrum of the solar simulator is completely consistent with the standard solar spectrum, and the other case is that the spectral response of the measured solar cell is completely consistent with the spectral response of the standard solar cell. These two special cases are difficult to strictly realize, but in contrast, the latter case is more difficult to realize, because the solar cells to be tested are diverse, and it is impossible for each cell to be tested to be equipped with a standard solar cell completely consistent with its spectral response. The reason why the spectral response is difficult to control is that, on the one hand, due to the process, under the influence of many complex factors, even the solar cells produced in the same process, structure, material or even in the same batch can not guarantee that they have exactly the same spectral response; On the other hand, due to the difficulty of testing, the measurement of spectral response is much more troublesome than volt ampere characteristics, and it is not easy to measure correctly. It is impossible to measure the spectral response of each solar cell before measuring volt ampere characteristics. Therefore, in order to improve spectral matching, the best way is to design a precision solar simulator whose spectral distribution is very close to the standard solar spectrum. The standard stipulates that the ground standard sunlight spectrum adopts the AM1.5 standard sunlight spectrum of total radiation, and the total irradiance of ground sunlight is specified as 1000W / m²。 The standard test temperature is specified as 25 ℃. If the test can only be carried out under non-standard conditions due to objective conditions, the measurement results must be converted to standard test conditions.

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