## 2 Modern Recycling Technologies for PV Panels and Wind Turbines: A Systematic Literature Review
### Modern Technologies of Blade Recycling  
The simplest method of recycling a composite material is mechanical (cutting, crushing, crumpling). However, it damages individual fibers, which leads to a decrease in mechanical characteristics. According to the data [49], the tensile strength of recycled fiberglass compared to new is not more than 78%; for carbon fiber, it is less than 50%, with the fiber recycling ratio (recyclate yield rate) of 55-58% of the initial mass. The material recycled in this way has a low cost and cannot be a substitute for the virgin material. Typically, such a recycled composite material is used for less demanding mechanical applications, for instance, aggregates for artificial wood or asphalt and concrete in the construction industry [50; 51]. Recycled carbon fiber (CF) is also suitable for short-fiber nonwoven composites used in aircraft and vehicle interiors [52]. Manufacturers can use recycled material as a filler or strength enhancer in new products, reducing the cost and environmental impact of waste disposal. In addition, recycled CF can be mixed with a polymer to produce thermally and electrically conductive materials used to improve the durability of paint, cement, and other construction materials [36; 53]. Other actively developed methods for processing composite materials are pyrolysis, oxidation in a fluidized bed, and chemical decomposition of polymer resins (binders) [54]. During pyrolysis, the composite is heated to 450-700 \({}^{\circ}\)C in the absence of oxygen. The polymer resin is evaporated, and the fibers remain intact and can be restored entirely [36]. The recyclate yield rate of both carbon and glass fibers during pyrolysis is 67-70% of the original mass. The residual tensile strength is 52% for fiberglass and 78% for carbon fiber [49]. During oxidation in a fluidized bed, the polymer component (resin) is burned in a stream of hot (450-550 \({}^{\circ}\)C) air enriched with oxygen. The carbon fiber recyclate yield rate is higher and reaches 86-90% of the initial mass, while for fiberglass, it is 42-44% [49]. The residual tensile strength is 50% for fiberglass and 75% for carbon fiber. The chemical influence on the binder polymer element, selected directly for a specific combination of fiber and polymer matrix, helps to get the maximum possible amount of fiber suitable for reuse with minimal time and resources. The recyclate yield rate of both carbon and fiberglass is almost 100% [49], the residual tensile strength for fiberglass is 58%, and for carbon fiber, it is 95%. To the best of our knowledge, the economic characteristics of the various processes of recycling of composite materials are absent in the literature because all of the methods mentioned above are still at the stage of laboratory research. Meanwhile, the data on the current energy intensity of these methods are known, which in combination with data on recycling efficiency, allow us to judge the competitiveness of methods from an economic point of view indirectly (Table 1). However, economic feasibility depends not only on the cost of the production process but on the availability and size of the market for recycled materials. Therefore, the prospects of the above methods for recycling blades of wind turbines are also determined by the fact that they are suitable for the recycling of  
Figure 4: The share of leading countries in the production of the world’s silicon supply. Source: based on data [48]. composite wastes from other sectors of the economy (aircraft, automotive). Therefore, the cost of their development and practical application can be reduced due to economies of scale. The possibility of incinerating composite materials in municipal waste plants for energy recovery depends on the ratio of polymer to carbon fiber in its composition [50]. A significant disadvantage of incinerating composite material is that approximately 60% of the initial mass remains in the form of ash. Ashes must also be disposed of in some way.