Matraeva, Liliia V., et al. “Methodological Approaches to Estimation of Energy Efficiency Within the Framework of the Concept of Green Economy and Sustainable Development”. International Journal of Energy Economics and Policy, vol. 7, no. 4, Sept. 2017, pp. 231-9, https://econjournals.com.tr/index.php/ijeep/article/view/5288.