## 2 Modern Recycling Technologies for PV Panels and Wind Turbines: A Systematic Literature Review
### Ecology Issues of Renewable Energy Sources (RES)-Capacity Recycling
A closer look at the literature on the EoL of wind turbines reveals that the most difficult components for recycling are the blades and the concrete foundation [27; 28]. The blades are currently simply landfilled or, in some cases, incirated at municipal waste plants. As they are made from composite materials, their recycling is very complicated. In cases where it is technologically possible, the recovered materials have much lower quality than virgin materials [29; 30]. It does not allow us to reuse them for the same purposes. In addition, the large sizes of the blades, which can reach 80-90 m in length on modern turbines, make it difficult to transport them to the place of recycling. The landfill of large volumes of wind turbine blades is a severe environmental and economic problem [31]. The mass of the blades of modern wind turbines reaches 12.37-13.41 tons per 1 MW, and for turbines ending their life in the coming years, it is about 8.34 tons per 1 MW [32]. It means that if in 2020, it is necessary to landfill more than 31,000 tons of blades, in 2025, this amount will be already more than 142,000 tons, while in 2030, this number will be more than half a million tons. Landfilling of such large objects will require their preliminary energy-intensive shredding or cutting. The EoL treatment of offshore wind turbines is an even more significant problem. Although their share in the total volume of wind turbine installations is much lower (Figure 3), they are more susceptible to adverse environmental effects and have a shorter lifetime. Thus, for example, in 2015, the first 10 MW Yttre Stengrund Swedish wind farm was decommissioned after only 15 years of operation [33]. In 2018, Utgrunden I Marine Wind Park (10.5 MW, Sweden) was decommissioned,  
Figure 2: Historical development of annual new wind turbines installations (in GW) and anticipated decommissioning until 2035. Source: based on [26]. which had operated for 18 years. In 2013, the first marine park built in the UK by Blyth (4 MW) ceased to operate after 13 years. Due to the lack of a clear demolition program, it is still abandoned in its original location. The Beatrice Demonstration Project (10 MW, UK) met the same fate. From a logistical point of view, the process of dismantling a marine wind park is much more complicated. Besides, there is currently no clear understanding of whether it is necessary to completely dismantle the foundation of wind turbines or they must be left in the same place [34]. Several methods are being developed in the literature to extend the lifetime of marine parks, which are based on the common idea of their more or less large-scale re-equipment. Some academicians have suggested replacing the engine, gearbox, and turbine blades and reusing the old tower, foundation, and power grid [33]. Others have suggested replacing all wind farm equipment except the foundation, which can last up to 100 years [35]. The implementation of such re-equipment is expected to reduce costs compared with the construction of new offshore wind farms [33]. Still, it does not entirely solve the disposal problem. From an economic point of view, the extraction of valuable materials from used blades is of more interest. For example, Vestas' blades are made up of glass fiber, carbon fiber (CF), epoxy resin, and polyurethane [36]. Carbon fiber (CF), in addition to wind energy, is also actively used in aircraft, automotive, shipbuilding, and other industries. Carbon fiber is produced from light fractions of crude oil, propane, and propylene through a multistage chemical treatment that requires significant energy costs. The production of one kg of carbon fiber requires 165 kWh, while the recovery is only 8.8 kWh. According to [37], the energy intensity of the glass fiber recycling is 10 times less than that of its production. Some European countries, especially the ones the most committed to the concept of developing a circular economy, prohibit the disposal of unprocessed waste with a high organic component at the legislative level.