## 2 Modern Recycling Technologies for PV Panels and Wind Turbines: A Systematic Literature Review
### Modern Technologies of PV Panel Recycling  
The modern industrial algorithm for recycling silicon-based photovoltaic panels begins with their disassembly, during which aluminum (frame) and glass parts (coating) are separated. Almost 95% of the glass is recyclable, and all external metal parts can be reused to form new frames for solar modules [38]. The remaining materials are heat-treated at a temperature of 500 \({}^{\circ}\)C, during which the encapsulating plastic evaporates, leaving the silicon elements ready for further processing. In modern recycling plants, evaporating plastic is not released into the environment but used as a heat source for further heat treatment (energy recovery technology), which partially reduces adverse environmental effects [15; 16; 39].  
After heat treatment, 80% of the PV modules (by mass) can be reused, while the rest is subject to additional cleaning. Silicon particles contained in cracked and scratched wafers are etched with acid and then melted for reuse to produce new silicon modules, resulting in an 85% level of recovery of the raw silicon material. The reuse of silicon can significantly reduce the adverse environmental effects of silicon photovoltaic panel manufacturing by saving, in addition to silicon sand itself, a significant amount of energy and water used in the production stage of metallurgical silicon. Based on the data of [PERSON] and co-authors [16], it is possible to estimate the energy savings in the manufacturing of 1 kW of a photovoltaic panel due to the reuse of silicon as 76.2 kWh and water savings as 76.2 L. It avoids an average emission of 123.34 kg of CO\({}_{2}\), 3.36 kg of SO\({}_{2}\), and 0.73 kg of NO\({}_{\mathrm{x}}\).  
The recycling of thin-film photovoltaic panels is more complicated [21; 40]. In the first step, the panel is crushed to a particle size of not more than 4-5 mm, which allows the removal of the lamination that holds the internal materials. Unlike silicon panels, the remaining substance consists of both solid and liquid materials, which need to be separated. Liquids pass through a precipitation and dehydration process to allow the recovery of semiconductor materials. Separation of semiconductor metals is carried out in various ways, depending on the technology used in the manufacture of panels; however, an average recovery rate of 95% is achieved. Solids contaminated with so-called interlayer materials are cleaned by vibration. Furthermore, the material undergoes washing, as a result of which there remains clean glass that must be melted and reused [39].  
There are some new technologies for recycling photovoltaic silicon modules at the stage of laboratory research: technology for dissolving a laminating film in an organic solvent (tetrahydrofuran, o-dichlorobenzene or toluene), technology for dissolving with additional ultrasonic treatment, hot cutting, pyrolysis, technology for dissolving in nitric acid, and some others [41; 42]. For thin-film modules, in addition to organic solvent dissolution and hot cutting technologies, laser exposure, vacuum processing, and flotation technologies are also being developed [43; 44].  
Previous studies have shown that the recycling of silicon modules becomes feasible at a scale of at least 19,000 tons per year [45]. Only when such volumes are achieved, the cost of processing decreases due to the economies of scale. The economic feasibility of recycling an entire PV panel is much higher than the expediency of recycling PV modules only, since the metal frame and electrical cables are easier to recycle, and the recovered materials (aluminum, copper) are valued higher [46; 47]. The economic feasibility of recycling silicon panels substantially depends on the price of new modules, which has fallen significantly in recent years. For example, for Europe, the commercial attractiveness of silicon recycling is also determined by the lack of its mining (Figure 4). Of all the European countries, only Norway has a share of more than 4% in the global silicon production market.