Frodyma, Katarzyna. “The Market of Renewable Energy Sources in the European Union - a Statistical Analysis”. Krakow Review of Economics and Management Zeszyty Naukowe Uniwersytetu Ekonomicznego W Krakowie, no. 5(941), Nov. 2015, pp. 63-78, https://doi.org/10.15678/ZNUEK.2015.0941.0505.