**6. Conclusions**

Even though assessing the environmental impact of the life cycle of the fastest-growing types of renewable energy is a popular topic in scientific literature, it has still not been studied enough. The particular difficulty is the study of the recycling of obsolete solar and wind power equipment. The first reason for this is the complexity of the methodological approach, which involves the distribution of all the positive effects created in the recycling process to earlier stages of the life cycle. The second reason is the great uncertainty of the current estimates, both due to the lack of primary data and because of the variety of logistic solutions for supply chains.

This study systematizes the most recent and relevant LCA results and identifies, based on the comparison, the patterns that work under any assumption about the technology and organization of the recycling process. The paper concludes by arguing that the contribution of further improvements in PV recycling technologies to environmental impacts throughout the entire life cycle is insignificant. Therefore, it is more beneficial to focus further efforts on economic parameters, in particular, on achieving the economic feasibility of recycling small volumes of PV waste. In the case of wind power, broadly translated, our findings indicate that the issue of transporting bulky components of wind turbines to and from the installation location is critical for improving the eco-design of the entire life cycle.

These patterns can now be the basis for the design of production systems for generating electricity and thereby contribute to the development of a circular economy. It is important to note that those countries that are still at the beginning of the path of renewable energy development (for example, Russia) can take into account the positive and negative experiences of the leading countries and optimize their production systems at the very early stages of their development.

The main practical conclusion that can be drawn from this study is that in order to improve the environmental performance of solar and wind power plants, Russia needs to develop accurate data centers for the forecasting of waste flow. It will help to elaborate a reasonable proactive strategy and optimize the number and locations of recycling plants.

Future research should further develop and confirm these initial findings by monitoring the progress in RES environmental performance on each stage of their life cycles. In addition, the comparison of less developed RES technologies with an LCA "cradle-to-grave" approach might prove an important area for future research.

**Author Contributions:** Conceptualization, S.R. (Svetlana Ratner); Data curation, S.R. (Svetlana Ratner); Formal analysis, I.L.; Funding acquisition, I.L.; Investigation, S.R. (Svetlana Ratner); Methodology, S.R. (Svetlana Ratner); Project administration, S.R. (Svetlana Revinova); Resources, K.G.; Software, S.R. (Svetlana Ratner); Supervision, S.R. (Svetlana Ratner); Validation, S.R. (Svetlana Ratner), K.G. and S.R. (Svetlana Revinova); Visualization, K.G.; Writing—original draft, S.R. (Svetlana Ratner); Writing—review & editing, S.R. (Svetlana Ratner), K.G., S.R. (Svetlana Revinova) and I.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** The publication has been prepared with the support of the «RUDN University Program 5–100».

**Conflicts of Interest:** The authors declare no conflict of interest.

*Appl. Sci.* **2020**, *10*, 4339
