[Bill of energy efficiency. (2011). EU, Brussels, Maszynopis.]Search in Google Scholar
[Borek, K., Barwicki, J., Majchrzak, M., Mazur, K., Wardal, W. (2015). Evaluation of the impact of digestate formed during biogas production on the content of heavy metals in soil. Agricultural Engineering, No 2, 15-23]Search in Google Scholar
[New developments in Lawrence Berkeley National Laboratory. (2013). USA.]Search in Google Scholar
[Information of Sustainable Energy Financial Facility. (2013). Warsaw.]Search in Google Scholar
[Information of the National Fund for Environment Protection and Water Management. (2012). Warsaw, Poland.]Search in Google Scholar
[Resolution of the Council of Ministers No. 202/2009 on the Polish Energy Policy until 2030, Brussels, Belgium.]Search in Google Scholar
[Solar collector market in Poland 2010. Institute for Renewable Energy, Warsaw, Poland]Search in Google Scholar
[Solar thermal markets in Europe. Trends and market statistics 2010, European Solar Thermal Industry Federation]Search in Google Scholar
[MIT new developments on energy projects – University information. (2013). New York, USA.]Search in Google Scholar
[Renewable energy sources in 2010. Central Statistical Office of Poland (GUS)]Search in Google Scholar
[Research activity in Oregon State University. (2013). Oregon, USA.]Search in Google Scholar
[Solar Botanic developments on renewable technologies. (2013). London.]Search in Google Scholar
[University of Texas research activity information. (2012). Texas, USA.]Search in Google Scholar
[Interreg EU - Baltic Sea Region - Baltic Slurry Acidification Project 2016-2019]Search in Google Scholar
[Project agreement BIOSTRATEG1/269056/5/NCBR/2015 z dnia 11.08.2015]Search in Google Scholar
[Wardal, W.J. et al., (2015). Technical and economical aspects of biogas production from agricultural sources including Polish conditions. Agricultural Engineering, No. 2(154), 137-148.]Search in Google Scholar
