## 3 Methodology and Data
If the life cycle of the product also includes the recycling stage, the modeling and calculation of the total adverse environmental effects are complicated by the fact that the recycled product can enter the production cycle again. In this case, it reduces the need for some raw materials. In modeling the processes of recycling, two main approaches are used: the \"cut-off approach\" and the \"end-of-life approach\". When using the first approach, the recycling efforts are economically allocated among the treatment process and all the recovered materials with a positive economic value. In the second approach, the potential benefits from the usage of recycled materials are calculated by awarding credits for the avoided environmental impacts caused by the primary production of replaced products. At the same time, some researchers use a simplified approach called open-loop recycling (OLR), in which further flows of secondary materials are not taken into account [57]. More details about differences in allocation approaches can be found in [38]. When choosing the technology for generating electricity from several possible options by environmental parameters, we are faced with the need to take into account the full life cycle of the electricity plant, including the recycling of massive generating equipment. The first stages of the life cycle of wind and solar energy are relatively well studied using LCA. For example, [6; 39; 58] compare a broad spectrum of environmental categories of photovoltaic technologies, [59] studies a life cycle of organic photovoltaics, and [60; 61; 62] compare GHG emissions of several photovoltaic technologies. Other studies [63; 64; 65] give life cycle assessments of solar panels manufactured in specific locations. Ecological aspects of the disposal of used equipment have also been studied (e.g., [66]). In contrast, accounting for recycling as a primary route for end-of-life treatment is a complex problem [38]. First, as a rule, when conducting an LCA for an electricity plant, 1 kWh of energy produced over the entire life of the equipment is used as a functional unit. Such a choice of a functional unit is convenient because it allows one to compare the results of LCA for different technologies and make a choice in favor of the most environmentally friendly. In LCA of the recycling of used generating equipment, the mass of the equipment itself (PV panel or wind turbine) usually is considered as a functional unit. Therefore, it is impossible to directly aggregate the LCA results of the first and last stages of the life cycle. The second difficulty is the lack of a universal approach to determining the system's boundaries for recycling processes. Some researchers include the collection and transportation of used PV panels and wind turbines, while others suggest that recycling is done directly at RES plant location. The third difficulty is that, as noted above, most of the recycling processes of RES capacities are at the stage of laboratory research, so the data on the inputs and outputs of these processes are minimal and have great uncertainty. This study systematizes the LCA results of various methods of EoL treatment of used PV panels and wind turbines, brings them to single units of measurement, and converts them to functional units used to evaluate the earlier stages of the life cycle of electricity plants. The conversion to the functional unit of 1 kWh of all estimations from the literature was carried out under the assumption that the capacity factor of PV plant is 14% [12], solar irradiation in the location of PV plant is 1200 kWh/m\({}^{2}\)/year [12], the weight of the 200 Wp c-Si module is 16.8 kg [16], the weight of 1 m\({}^{2}\) of the module is 13.2 kg [67], the weight of 1 m\({}^{2}\) of the CdTe module is 14.63 kg [67], and the module efficiency is 10.5% [67]. The primary difference of the present research in comparison with similar ones is that we did not restrict ourselves with a certain LCIA method and considered a maximally wide spectrum of impact categories.