2.1. Characteristics of the Photovoltaic Market in the EU
In recent years, there has been a dynamic growth of the photovoltaic market in the EU. One of the most important reasons for this trend is the significant development of photovoltaic technologies, which results in decreased prices. Generally, it can be stated that this form of obtaining electricity has become price-competitive compared to traditional energy sources [
5]. An important aspect is the system of subsidies, which has been enforced in various forms in some countries, including many European ones. In 2021, the total installed capacity in PV was almost 158 GW, which is 18.7% of the total installed capacity in PV globally. Compared to the previous year, this is an increase of approximately 16%.
Figure 1 shows the top 10 markets for PV technology in the EU. The data characterizing individual markets include the installed capacity in PV in GW and the amount of electricity produced from PV in TWh for 2021 [
16,
17,
18].
In the EU, Germany is the leader, with a PV capacity of 58.5 GW. Italy is ranked second, with 22.7 MW of installed PV capacity. They are followed by France, the Netherlands and Spain. These countries have the capacities of PV installations equal to approx. 14 GW. The last one in the top ten is Hungary, which has an installed PV capacity of 2.1 MW. Thus, there is a significant difference between the leader and the last country, which is still at the forefront of Europe. In terms of gross electricity production, the ranking is similar, although there are changes in the positions of individual countries. Countries with very good insolation conditions gain. As a result, their annual electricity production reaches high efficiency, such as in Spain and Greece [
18,
19].
Figure 2 [
20] shows a geographical comparison of European countries in terms of irradiation and EPBT (energy payback time). The intensity of solar radiation per 1 m² of surface (irradiation) translates into the amount of electricity produced. Depending on the geographical location, the difference can be significant. The second indicator confirms this trend. The payback period for PV installation is shorter for regions with higher irradiation.
Portugal and Italy, as well as the Balkan countries, Romania, Bulgaria and the southern part of France, also have very good geographical conditions for solar energy. This is conducive to the development of PV technology.
According to forecasts [
5,
6], PV technology will account for an increasing share in electricity production. In addition, the EU climate policy, defined, e.g., as part of the Renewable Energy Directive, sets a target for the share of renewable sources in energy production of 40%, with the possibility of increasing to 45% [
21]. One of the key technologies to achieve this goal will be PV.
2.3. Methods of the Photovoltaic Panels Recycling
Photovoltaic panels are generally classified as belonging to three generations: I, II and III. The first generation includes crystalline silicon (c-Si) panels. They constitute the vast majority (approx. 95%) of currently used panels [
23]. Second-generation modules account for about 5%, while third-generation panels are practically not considered in real-scale installations. The first generation includes crystalline silicon panels: mono- and polycrystalline (also known as multicrystalline). The second generation includes thin-film technologies: cells based on amorphous silicon (aSi) and silicon-free cells—CIGS (copper indium gallium selenide), CdTe (cadmium telluride) and perovskite. Among the modules with crystalline cells, monocrystalline cells are currently more often used, while in the case of the second generation, the use of CdTe cells prevails. The last generation includes dye cells, which are based on the phenomenon of photosynthesis [
24,
25].
In general, recycling methods can be divided into downcycling and upcycling. Downcycling is so-called low-value recycling, which recovers materials of lower purity that are therefore more difficult to reuse. Upcycling in reverse recovers materials of higher purity or quality, suitable for reuse [
26].
Both approaches start with the same action, namely removing the aluminum frame, cables and junction box. In the next stage, other processes are already taking place. Downcycling is a simplified method that results in the recovery of most of the glass and aluminum. As a standard, the next stage is fragmentation of the module on the glass recycling line, crushing, and then glass and aluminum sorting processes. Partial recovery of ferrous metals also takes place here. The other components present in the module, i.e., silicon, metal residues, glass, plastic and aluminum, form a mixture that ends up in landfills. Hence, downcycling can be described as a simple method of recycling PV panels that does not require significant energy inputs or high investment costs and allows for a reduction in the landfilling of a significant amount of this type of waste. On the other hand, it limits the number of recoverable raw materials, as well as lower-quality recycled raw materials. In addition, the mixture remaining after the process may contain metals, the introduction of which into the environment should be limited, and high-calorie components that should not be landfilled [
27,
28,
29,
30].
Upcycling aims to recycle other components, e.g., Ag, Si, Cu, Cd, Te. The first common step is followed by a series of thermal, mechanical or chemical processes that allow for the recovery of many high-purity materials. This results in higher upcycling complexity, as well as higher investment and operating costs. In addition, the chemical or thermal processes used here require energy and the use of chemical compounds. Process products that require management, such as fly ash from thermal processes, should also be included. As part of upcycling, there are many methods dedicated to various types of PV modules, mostly crystalline silicon modules [
29,
31].
In general terms, the upcycling of first-generation solar panels includes the following steps:
removal of the aluminum frame, cables and junction box;
separation of the glass from the silicon wafer in a thermal, mechanical or chemical process;
separation and purification of silicon cells and special metals (e.g., silver, tin, lead, copper) using chemical and electrical techniques [
29].
The individual stages of downcycling and upcycling are presented in
Figure 3.
Thin-film panels require some modifications to the recycling processes. More detailed information on the technology of recycling photovoltaic modules can be found in articles [
27,
28,
29,
30,
31,
32,
33,
34,
35].
2.4. The Current State of Photovoltaic Waste Recycling in the EU
Although the amount of PV waste is not at a high level at the present time, the first recycling plants have already been built. Currently, they do not have high processing capacity. Rather, they are test installations, although they carry out recycling with a high recovery rate. The largest is the Veolia plant in France, which converts the PV modules delivered there with a recycling rate of 96% for c-Si PV modules [
33]. The organizer of the collection and transport of EoL PV panels here is PV Cycle. The scope of the company’s operations is similar to that of an operator in the deposit-refund system. Therefore, PV Cycle aims to create a voluntary and sustainable take-back program for EoL PV panels, and then subject them to the development. The system is currently being tested primarily in France, where 1300 Mg of panels were processed at the Veolia plant through PV Cycle in 2018. The plan for 2022 is 4000 Mg [
36,
37,
38].
Among the companies involved in the recycling of PV panels, the German companies Loser Chemie and Solar World can also be mentioned. Loser Chemie has several collection points where it collects several types of photovoltaic systems (c-Si, CdTe, CIGS). The company developed and patented original processes using mechanical and chemical treatment to recycle solar cells [
39]. SolarWorld [
40] also has its own c-Si recycling method. A significant number of laboratory tests are available for different methods of recycling photovoltaic panels. Some of the results are listed below.
The starting stage of upcycling is the separation of the glass from the solar cell. Between these two layers is a hard-to-remove layer of a bonding polymer–EVA (ethylene-vinyl acetate). Mechanical, thermal or chemical methods can be used for this purpose. As part of mechanical separation, grinding and crushing are most often used. A relatively high efficiency of glass recovery was obtained in the study [
41], where triple grinding was used, in which 91% of the glass was recovered. A different approach was used in studies [
33,
42]. In the first case, delamination was performed using a cryogenic process. In the second, a hot knife cut was used. This method turned out to be the most effective among mechanical methods, as it allowed for the recovery of 98% of glass [
42].
Among the methods of thermal delamination, the most commonly used process is pyrolysis. This allows for thermal decomposition of the EVA layer, which occurs at a temperature of approximately 500 °C within 1 hour. An undoubted advantage is the high recovery of glass and the preservation of the high quality of separated silicon cells. In the case of mechanical methods, this material is often of lower quality. The disadvantages of such a solution are high costs and energy consumption and the generation of harmful products of the thermal process [
43].
Chemical delamination methods rely on the use of inorganic and organic solvents. The characteristic features of this method are its duration, which can be up to several days, and high demand for chemicals. Currently, methods of significantly accelerating the process are being investigated. According to [
44], the process of dissolving the EVA layer in toluene using ultrasonic radiation takes less than 1 hour.
The next step in the recycling of PV panels is the separation of silicon and metals by leaching and etching, which require chemicals. The methods used here allow for the recovery of silicon. The implementation method affects the purity of the recovered material [
45,
46]. In the case of complex methods, it is possible to recover high-purity silicon, which can be reused in photovoltaic products. Simplified methods, usually preceded by an invasive mechanical process of separating the glass from the solar cell, result in the recovery of much lower-quality silicon [
42].
The last step of upcycling is the extraction of the metals left over from the leaching or etching process in solution, which can be accomplished by electrolysis, metallic replacement or chemical precipitation. In order to compare the effectiveness of these three methods, one can refer to [
47] on the recovery of silver from photovoltaic modules. The element recovery rates obtained were 89.7, 87.4 and 99.5%, respectively.
Based on the results of upcycling research available in the literature, the currently achievable recovery rates of individual materials contained in the EoL of photovoltaic panels were determined. Data are presented in
Table 1 [
41,
42,
43,
44,
45,
46,
47,
48,
49,
50,
51,
52].
Assessment of the environmental impact of recycling waste PV panels carried out by [
53,
54,
55,
56] indicates a significant advantage over other management methods. When comparing different recycling methods, the situation is difficult to evaluate unequivocally; however, chemical processes are mentioned as having the greatest impact on the environment [
31,
57]. Considering the economic aspect of recycling generally leads to the conclusion about the financial losses associated with the recycling of PV waste. Only in case of a stable, large stream of PV waste, the profitability of the recycling plant can be established [
51,
58].
Nevertheless, it should be noted that currently, the upcycling of photovoltaic panels does not take place on a large scale and is rather for demonstration [
26]. Photovoltaic waste that is not upcycled is currently downcycled, reused or stored. The exact waste streams for each management method have not been identified. However, it should be noted that the stream of this type of waste will increase every year. According to the prediction of [
5], the amount of PV waste in the world in the 2030 will be 1.7–8 million Mg.
One of the basic problems of recycling EoL photovoltaic panels is unprofitability. Current waste volumes are still low, implying economic impediments to the development of existing processes. Comparing the economics of recycling other WEEE waste, the profits from the sale of recovered materials are too small to cover the costs of upcycling PV waste. In addition, the production PV modules use less valuable materials, such as copper, silver or tellurium. This is an advantage of technology development for environmental impact. Paradoxically, however, this reduces revenues from the sale of secondary raw materials. Nevertheless, the extended producer responsibility (EPR) system and the growing EU targets for the recovery of materials, including from WEEE waste, are factors in favor of the development of upcycling methods towards increasing profitability, practicality and efficiency, as well as reducing environmental impact.