Conversion of energy with the highest possible efficiency is of primary importance in processes with high intensity of energy flows, among which the most significant are those in thermal power plants. The paper deals with the influence of coal composition on the conversions taking place in power plants. The analysis of energy conversions treats, above all, the heat loss due to the exhaust flue gas. The analyses of the power plants use of electric powers are focused on the processes of coal pulverising and exhaust flue gas cleaning. The results of the analyses are graphically presented.