The calculation of a turbo-expander impeller of a thermoelectric plant operating according to organic Rankine cycle (ORC) is given. The calculation was carried out for real gas using the Peng-Robinson model. Freon R245fa was chosen as the working fluid of the plant. The approximation values of the coefficients of polynomial describing the temperature dependence of isobaric heat capacity on Freon R245fa were used in the calculation.