A method for recycling waste photovoltaic modules

Abstract

This disclosure relates to a method for recycling waste photovoltaic modules, the method comprising: S1, removing the backsheet material from frameless waste photovoltaic modules; S2, applying a layer of fiber cotton under pressure to the cell side of the frameless waste photovoltaic modules with the backsheet material removed, to obtain pretreated waste photovoltaic modules; S3, subjecting the pretreated waste photovoltaic modules to pyrolysis. The method of this disclosure achieves extremely high recovery rates for glass and crystalline silicon cells in waste photovoltaic modules.

Description

Technical Field

[0001] This application relates to the field of new energy, and specifically to a method for recycling waste photovoltaic modules. Background Technology

[0002] With energy demand increasing daily, countries worldwide are vigorously developing the photovoltaic (PV) industry to alleviate global energy shortages. Statistics show that China's PV installed capacity has steadily grown from 12.9 GW in 2013 to 52.3 GW in 2017, accounting for over 50% of global installed capacity, making China the largest PV application market. However, PV panels have a lifespan of 25-30 years. Due to this long lifespan, the recycling of used PV panels has been largely neglected.

[0003] However, according to reports, photovoltaic (PV) panels, which were first installed in the 1980s and 1990s, have reached the end of their lifespan in recent years. Furthermore, due to advancements in PV technology, reduced photoelectric conversion efficiency, equipment damage, and module aging, the growth of waste PV panels has accelerated, attracting widespread attention. The amount of waste PV panels is expected to increase significantly after 2016, with global waste reaching 43,500-250,000 tons in 2016. It is projected that global waste will reach 1.7-8 million tons by 2030 and 60-78 million tons by 2050. In 2020, China alone produced approximately 500 tons of waste PV panels. It is projected that by 2050, China will have reached 20 million tons, equivalent to 2,000 times the weight of the Eiffel Tower. Therefore, it is foreseeable that a large amount of waste PV panels will need to be processed globally in the future.

[0004] Currently, existing research methods for recycling and processing waste silicon-based photovoltaic panels both domestically and internationally mainly include: physical treatment methods, chemical treatment methods, combined physical and chemical treatment methods, and external field enhancement methods. These methods primarily address the different characteristics of the components within the photovoltaic panels, achieving a certain degree of recycling. However, from environmental, economic, and industrial application perspectives, existing recycling processes still present some challenges.

[0005] High-temperature heat treatment increases the risk of silicon-based solar cells breaking. As the average thickness of polycrystalline silicon wafers decreases from 550 μm to 170 μm, this reduction in thickness further increases the risk of breakage during processing. Currently, it is difficult to recover intact silicon-based solar cells for direct remanufacturing of photovoltaic panels. Summary of the Invention

[0006] The purpose of this disclosure is to provide a method for recycling waste photovoltaic modules, which has an extremely high recovery rate of glass and crystalline silicon solar cells in waste photovoltaic modules.

[0007] To achieve the above objectives, this disclosure provides a method for recycling waste photovoltaic modules, the method comprising:

[0008] S1. Remove the backsheet material from frameless, waste photovoltaic modules;

[0009] S2. Apply a layer of fiber cotton to the cell side of the frameless waste photovoltaic module after the backsheet material has been removed to obtain the pre-treated waste photovoltaic module.

[0010] S3. Pyrolyze the pretreated waste photovoltaic modules.

[0011] Optionally, in step S2, the thickness of the fiber cotton layer is 3-8 mm, preferably 4-6 mm.

[0012] Optionally, the material of the fiber cotton layer is selected from one or more of aluminum silicate fiber cotton, asbestos, and glass fiber cotton.

[0013] Optionally, in step S3, the pyrolysis conditions include: an initial temperature of 20-35℃, an end temperature of 430-480℃, a heating rate of 3-8℃ / min, and a time of 1-4 hours.

[0014] Optionally, in step S3, the pyrolysis conditions include: an initial temperature of 25-30℃, an end temperature of 450-460℃, a heating rate of 5-6℃ / min, and a time of 3-4 hours.

[0015] Optionally, the removal of the backsheet material from the frameless waste photovoltaic modules includes: cleaning the waste photovoltaic modules and mechanically removing the frames of the waste photovoltaic modules, and then removing the backsheet material from the frameless waste photovoltaic modules at 120-140°C.

[0016] Optionally, the method further includes step S4: cooling after the pyrolysis is completed, wherein the cooling conditions include a cooling rate of 3-8℃ / min and an endpoint temperature of 20-35℃.

[0017] Optionally, in step S2, a fiber cotton layer is applied under pressure to the cell side of the frameless waste photovoltaic module with the backsheet material removed in the pressure application device.

[0018] Preferably, the frameless waste photovoltaic module with the backsheet material removed is placed horizontally along its length between two opposing pressure application surfaces of the pressure application device, and a layer of fiber cotton is laid on the cell side; the orthogonal projection area of ​​the frameless waste photovoltaic module with the backsheet material removed on the pressure application surface is smaller than the area of ​​the pressure application surface.

[0019] Optionally, in step S2, the pressure applied to both sides of the frameless waste photovoltaic module with the backsheet material removed is the same, and the pressure applied to one side is 5-10 Pa, preferably 7-8 Pa.

[0020] Optionally, in step S3, the pyrolysis is carried out in a tunnel kiln.

[0021] Through the above technical solution, this disclosure adopts the lamination pyrolysis method to recycle waste photovoltaic modules. It cleverly promotes the uniform release of pyrolysis gases through the fiber cotton layer, and can achieve the recycling of glass and crystalline silicon cells in waste photovoltaic modules with an extremely high recycling rate.

[0022] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0024] This disclosure provides a method for recycling waste photovoltaic modules, the method comprising: S1, removing the backsheet material of the frameless waste photovoltaic module; S2, applying a layer of fiber cotton under pressure to the cell side of the frameless waste photovoltaic module with the backsheet material removed, to obtain a pretreated waste photovoltaic module; S3, pyrolyzing the pretreated waste photovoltaic module.

[0025] Existing technologies that subject waste photovoltaic modules to high-temperature heat treatment increase the risk of silicon-based cell breakage. The inventors of this disclosure have unexpectedly discovered that by adding a layer of fiber cotton to the cell side of the waste photovoltaic module, the position of the crystalline silicon cell can be strengthened and fixed. At the same time, the gas generated by pyrolysis is released at a uniform rate, avoiding the breakage of the crystalline silicon cell due to the excessively rapid release rate of the large amount of carbon dioxide gas generated by pyrolysis. This allows for the recycling of glass and crystalline silicon cells from waste photovoltaic modules with an extremely high recycling rate. The method is simple, easy to implement, requires no consumables, and is suitable for industrial applications.

[0026] According to this disclosure, the thickness of the fiber cotton layer can vary within a wide range. In one embodiment of this disclosure, in step S2, the thickness of the fiber cotton layer is 3-8 mm, preferably 4-6 mm. In this disclosure, the thickness of the fiber cotton layer refers to its thickness before pressurization. If the fiber cotton layer is too thin, it may result in uneven pressure application to the photovoltaic module and fail to effectively promote uniform gas release; if the fiber cotton layer is too thick, the pressure transmitted to the photovoltaic module during pressure application will be too dispersed, also failing to effectively promote uniform gas release. A suitable fiber cotton layer thickness within the above range is more conducive to uniform gas release, thereby further improving the recycling rate of glass and crystalline silicon solar cells.

[0027] According to this disclosure, the material of the fiber cotton layer can be a high-temperature resistant fiber cotton well known to those skilled in the art, such as one that can withstand high temperatures of 1000-1500°C. In one specific embodiment of this disclosure, the material of the fiber cotton layer is selected from one or more of aluminum silicate fiber cotton, asbestos, and glass fiber cotton.

[0028] In one specific embodiment of this disclosure, the pyrolysis conditions in step S3 include: an initial temperature of 20-35°C, an ending temperature of 430-480°C, a heating rate of 3-8°C / min, and a time of 1-4 hours; preferably, the initial temperature is 25-30°C, the ending temperature is 450-460°C, the heating rate is 5-6°C / min, and the time is 3-4 hours. By precisely controlling the pyrolysis conditions as described above, an unsuitable gas release rate due to an excessively fast or slow heating rate can be avoided, further improving the recovery rate of glass and crystalline silicon solar cells.

[0029] In one specific embodiment of this disclosure, the removal of the backsheet material of the frameless waste photovoltaic module includes: cleaning the waste photovoltaic module and mechanically removing the frame of the waste photovoltaic module, and then removing the backsheet material of the frameless waste photovoltaic module at 120-140°C.

[0030] According to this disclosure, cleaning can be performed using methods well known to those skilled in the art to remove dust, oil, and other contaminants from the surface of waste photovoltaic modules. For example, one or more of the following methods can be used: ultrasonic cleaner, high-pressure water gun rinsing, and roller brush cleaning. Specific operating methods are well known to those skilled in the art and will not be elaborated upon here. According to this disclosure, the frame can be mechanically removed using methods well known to those skilled in the art, such as a frame disassembly machine.

[0031] In one specific embodiment of this disclosure, the method further includes step S4: cooling after the pyrolysis is completed, wherein the cooling conditions include: a cooling rate of 3-8℃ / min, an endpoint temperature of 20-35℃, and the glass and crystalline silicon solar cells are separated after cooling to the endpoint temperature. Under the above conditions, the recovery rate of glass and crystalline silicon solar cells can be further improved.

[0032] In one specific embodiment of this disclosure, in step S2, a fiber cotton layer is applied under pressure to the cell side of a frameless waste photovoltaic module with its backsheet material removed using a pressure-applying device. The pressure-applying device can be, for example, a hydraulic impact device or a hydraulic stretching device. Preferably, the frameless waste photovoltaic module with its backsheet material removed is placed horizontally along its length between two opposing pressure application surfaces of the pressure-applying device, and the fiber cotton layer is applied to the cell side. More preferably, the fiber cotton layer is applied to the uniform side of the cell. The projected area of ​​the frameless waste photovoltaic module with its backsheet material removed on the pressure application surface is smaller than the area of ​​the pressure application surface. In this embodiment, the fiber cotton layer adheres more tightly to the crystalline silicon cell, providing a better fixation effect and further promoting uniform gas diffusion during pyrolysis.

[0033] In one specific embodiment of this disclosure, in step S2, the pressure applied to both sides of the frameless waste photovoltaic module with the backsheet material removed is the same, with a single-side pressure of 5-10 Pa, preferably 7-8 Pa. In this embodiment, the appropriate pressure allows the fiber cotton layer to adhere more tightly to the crystalline silicon solar cell, resulting in better fixation of the crystalline silicon solar cell and further promoting uniform gas diffusion during pyrolysis.

[0034] According to this disclosure, pyrolysis can be carried out in an apparatus well known to those skilled in the art. In one specific embodiment of this disclosure, in step S3, the pyrolysis is carried out in a tunnel kiln.

[0035] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0036] In the following examples and comparative examples, the waste photovoltaic modules processed were from retired photovoltaic modules of the State Energy Group.

[0037] Example 1

[0038] S1. The waste photovoltaic modules are cleaned and dusted using an ultrasonic cleaning device. Then, the aluminum frame is removed by mechanical separation. The waste photovoltaic modules are heated to 120°C by a platform to remove the back sheet material.

[0039] S2. Place the frameless waste photovoltaic module with the backsheet material removed horizontally along its length between two opposing pressure application surfaces of the flat uniform pressure application device. Evenly lay 5mm thick aluminum silicate fiber cotton on one side of the cell and apply a pressure of 8Pa. The contact surface of the pressure application surfaces on both sides is larger than the size of the frameless waste photovoltaic module with the backsheet material removed.

[0040] S3. Set the tunnel kiln to a heating program with a pyrolysis heating rate of 5℃ / min, an initial temperature of 25℃, an ending temperature of 450℃, and a pyrolysis time of 3 hours. After heating is complete, set a stable cooling program with a cooling rate of 5℃ / min. Once the temperature has dropped to room temperature, remove the glass plate and the crystalline silicon solar cell. At this point, the glass plate and the crystalline silicon solar cell are completely separated.

[0041] The experiment was repeated 10 times. In each group of experiments, the crystalline silicon solar cell and the glass could be completely separated without the crystalline silicon solar cell breaking.

[0042] Example 2

[0043] Waste photovoltaic modules were recycled using the same method as in Example 1, except that in step S2, aluminum silicate fiber cotton with a thickness of 3 mm was evenly laid on one side of the cell.

[0044] The experiment was repeated 10 times. In 8 of the experiments, the crystalline silicon solar cell and the glass could be completely separated without the crystalline silicon solar cell breaking. In 2 of the experiments, the crystalline silicon solar cell broke.

[0045] Example 3

[0046] Waste photovoltaic modules were recycled using the same method as in Example 1, except that in step S2, aluminum silicate fiber cotton with a thickness of 8mm was evenly laid on one side of the cell.

[0047] The experiment was repeated 10 times. In 7 of the experiments, the crystalline silicon solar cell and the glass could be completely separated without the crystalline silicon solar cell breaking. In 3 of the experiments, the crystalline silicon solar cell broke.

[0048] Example 4

[0049] Waste photovoltaic modules were recycled using the same method as in Example 1, except that in step S3, the tunnel kiln was programmed to heat at a pyrolysis rate of 8°C / min, with an initial temperature of 25°C and an ending temperature of 480°C, for a pyrolysis time of 3 hours. After heating was complete, a stable cooling program was set, also at a cooling rate of 8°C / min. Once the temperature had dropped to room temperature, the glass plate and crystalline silicon solar cells were removed, at which point the glass plate and crystalline silicon solar cells were completely separated.

[0050] The experiment was repeated 10 times. In 7 of the experiments, the crystalline silicon solar cell and the glass could be completely separated without the crystalline silicon solar cell breaking. In 3 of the experiments, the crystalline silicon solar cell broke.

[0051] Example 5

[0052] Waste photovoltaic modules were recycled using the same method as in Example 1, except that in step S3, the tunnel kiln was programmed to heat at a pyrolysis rate of 8°C / min, with an initial temperature of 25°C and an ending temperature of 430°C, for a pyrolysis time of 3 hours. After heating was complete, a stable cooling program was set, also at a cooling rate of 8°C / min. Once the temperature had dropped to room temperature, the glass plate and crystalline silicon solar cells were removed, at which point the glass plate and crystalline silicon solar cells were completely separated.

[0053] The experiment was repeated 10 times. In 6 of the experiments, the crystalline silicon solar cell and the glass could be completely separated without the crystalline silicon solar cell breaking. In 4 of the experiments, the crystalline silicon solar cell broke.

[0054] Comparative Example 1

[0055] Waste photovoltaic modules were recycled using the same method as in Example 1, except that step S2 was omitted. This experiment was repeated 10 times, and in all 10 experiments, the crystalline silicon solar cells were completely broken.

[0056] As can be seen from the above, the method disclosed herein is simple and easy to implement, and can achieve a high recycling rate for glass and crystalline silicon solar cells in waste photovoltaic modules.

[0057] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0058] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0059] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for recycling waste photovoltaic modules, the method comprising: S1. Remove the backsheet material from frameless, waste photovoltaic modules; S2. Apply a layer of fiber cotton to the cell side of the frameless waste photovoltaic module with the backsheet material removed in the pressure device to obtain the pre-treated waste photovoltaic module. S3. Pyrolyze the pretreated waste photovoltaic modules. In step S2, the frameless waste photovoltaic module with the backsheet material removed is placed horizontally along its length between two opposing pressure application surfaces of the pressure application device, and a layer of fiber cotton is laid on the cell side. The projected area of ​​the frameless waste photovoltaic module with the backsheet material removed on the pressure application surface is smaller than the area of ​​the pressure application surface.

2. The method according to claim 1, wherein, In step S2, the thickness of the fiber cotton layer is 3-8 mm.

3. The method according to claim 2, wherein, In step S2, the thickness of the fiber cotton layer is 4-6 mm.

4. The method according to claim 1, wherein, The material of the fiber cotton layer is selected from one or more of aluminum silicate fiber cotton, asbestos and glass fiber cotton.

5. The method according to claim 1, wherein, In step S3, the pyrolysis conditions include: an initial temperature of 20-35℃, an end temperature of 430-480℃, a heating rate of 3-8℃ / min, and a time of 1-4 hours.

6. The method according to claim 1, wherein, In step S3, the pyrolysis conditions include: an initial temperature of 25-30℃, an end temperature of 450-460℃, a heating rate of 5-6℃ / min, and a time of 3-4 hours.

7. The method according to claim 1, wherein, The removal of the backsheet material from frameless waste photovoltaic modules includes: cleaning the waste photovoltaic modules and mechanically removing the frames of the waste photovoltaic modules, and then removing the backsheet material from the frameless waste photovoltaic modules at 120-140℃.

8. The method according to claim 1, wherein, The method further includes step S4: cooling after the pyrolysis is completed, wherein the cooling conditions include a cooling rate of 3-8℃ / min and an endpoint temperature of 20-35℃.

9. The method according to claim 1, wherein, In step S2, the pressure applied to both sides of the frameless waste photovoltaic module with the backsheet material removed is the same, and the pressure applied to one side is 5-10 Pa.

10. The method according to claim 9, wherein, In step S2, the pressure applied on one side is 7-8 Pa.

11. The method according to claim 1, wherein, In step S3, the pyrolysis is carried out in a tunnel kiln.