Cucchiella, F., I. D’Adamo, and M. Gastaldi. “Profitability Analysis for Biomethane: A Strategic Role in the Italian Transport Sector”. International Journal of Energy Economics and Policy, vol. 5, no. 2, Apr. 2015, pp. 440-9, https://www.econjournals.com/index.php/ijeep/article/view/1100.