Paunkov, N., R. Popov, R. Manatbayev, N. Kalasov, E. Zulbuharova, A. Tulepbergenov, S. Nedelcheva, and A. Georgiev. “Efficiency Comparison of Photovoltaic and Photovoltaic-Thermal Solar Panels”. International Journal of Mathematics and Physics, vol. 8, no. 1, June 2017, pp. 28-33, doi:10.26577/ijmph.2017.v8.i1.05.