# Renewable Energy and Sustainability from the Supply Side: A Critical Review and Analysis
## 6 Conclusions and Research Prospects
First, the variety of renewable energies explored in the literature that address cases in developed countries is greater than the variety of renewable energies analyzed in the context of developing countries. In the sample articles focusing on low-income countries, biomass and hydroelectric energy are the only two types of renewable energies that have been studied. This resembles the empirical evidence on the energy ladder, according to which more developed countries invest more in more diversified renewable energy sources in their energy mix. This result also reveals the difference between the research unit focused on by academics and reality. According to the 2018 report on Global Trends in Renewable Energy [188], developing countries made up more than 60% of investment in renewable energy of the global investment, while the share of developed economies is only around 37%. This would indicate that most of the cases focused on by academics should be in developing countries, but this was not the case. According [PERSON] [189], the choice of examining developed countries instead of developing countries is due to the fact that countries with higher average income tend to care more about the environment than those with lower average income, thus the study of renewable energies and sustainability is more appropriately undertaken in these countries. Second, this study also supports that the environmental dimension of sustainability is the overwhelming concern among studies addressing countries of all development levels. In fact, even for lower income countries, economic sustainability concerns are a minority among all the literature reviewed and social sustainability concerns is not representative. Third, the wind-solar type of energy is the most focused on in the sample articles, with the environmental sustainability alone or with the economic sustainability as the most investigated. This reflects what is observed in reality and reported by the Renewables 2019 Global Status Report [190], which states that the global renewable energy sector is on an upward trend with the wind and solar sources of energies increasing their shares. Moreover, wind and solar energy systems are natural complements since solar power concentrates during the daytime, whereas wind power has greater output at night [191; 192]. The main conclusion that can be drawn is that the environmental dimension of sustainability alone or with other sustainability dimensions is the most explored and the social dimension of sustainability is the least. Biodiesel is clearly the exception to the pattern. In the articles focusing on this energy source, social and economic dimensions of sustainability prevail over the environmental dimension. A further analysis of the results of this research highlights some contradictory views about the issue when coming from the political discourse, empirical evidence, and our own review of the literature. In fact, there are contradictory views coming from the political arena of some of the world's leaders vis-a-vis the Sustainable Development Goals of the United Nations. However, although empirical evidence points to a one-way path that combines development and the energy mix with a high emphasis on modern renewable energies, the literature review reveals a lack of research on developing countries and those modern sources of renewable energies. Furthermore, it reveals a lack of analysis on the relationship between renewable energies adoption or investments and social dimensions such as poverty, inequality, and employment. Summing up, the state of the art of the literature may induce a further delay for developing countries to adopt cleaner technologies in their energy production. As these findings are independent of the authors' affiliation, there is a need and an opportunity to re-focus the literature on studying the implementation of cleaner renewable energies in developing countries.