# Renewable Energy and Sustainability from the Supply Side: A Critical Review and Analysis
## 6 Conclusions and Research Prospects  
The literature bridging renewable energies and sustainability was analyzed, providing the first critical literature review on the issue that considers the three dimensions of sustainability simultaneously. To this end, we reviewed and analyzed 316 articles published from 1997 to 2019. To guide the analysis, three research questions were devised: \"Are there differences between the type of renewable energy focused on in the articles and the level of development of countries in which they are analyzed?\"; \"Are there differences between the dimension of sustainability focused on in the papers and the country's development level?\"; and \"Are there differences between the type of renewable energies focused on and the dimension of sustainability analyzed in the articles?\"  
Most works on renewable energies and sustainability are concerned with environmental problems, mainly those focusing on biomass and wind-solar sources of energies and attempt to find solutions to make the renewable energy production supply chain more sustainable using suitable policies and investments in the economy. In fact, some authors alert the scholarly community to the importance of a set of factors that seems to be responsible for the success of the renewable energy production: (i) the optimization of supply chains and logistics management [181]; (ii) the capacity and location of supply, collection, and processing centers [182]; and (iii) the supplier selection and the SC network design [183]. Regarding the type of renewable energies most focused on in the sample articles, biofuel appears as the most examined followed by biomass, with biodiesel as the least investigated. The most productive countries in terms of renewable energies and sustainability concerns in the sample are USA, Brazil, European Union, China, and UK. The research community that studies the relationship between renewable energies and sustainability covers 55 countries, most of which are regarded as high development countries. In another work about the economy, energy, and environment [184], also using a bibliometric analysis as methodology, the same countries were identified as the main contributors to the development of that research field: China, USA, UK, and some European Union countries (Italy, Germany, Spain, France, and the Netherlands). The important contribution of the European Union to the advances in renewable energies and sustainability derivesalso from the Energy Union Package [185] in 2015. This is a Framework that gives priority to energy policies being supported in the following five priority areas: (1) decarbonization; (2) energy efficiency; (3) internal energy markets; (4) energy security; and (5) research, innovation, and competitiveness. This will lead to the adoption of national policies and monetary incentives motivating the research on renewable energies (energy efficiency) and sustainability (decarbonization). In China, the research topic of renewable energies and sustainability has also increased, supported mainly by the Energy Research Institute of China and the Special Fund arrangement created in 2006, which offers subsidies and grants to renewable energy players such as manufacturers and research institutions in the production and technological innovation of renewable energies with sustainability concerns. Moreover, China's National Mid- and Long-term Plan for Science & Technology (2006-2020) has also been an important driver in this increased tendency [186]. In USA, several energy efficiency and renewable energy programs are responsible for supporting much of the research published in top journals, for example the Renewable Energy Research and Development Program provides financial assistance to conduct balanced research and development efforts in renewable energies and has existed since the 1970s [187]. The main conclusions are as follows.