In this paper an universal analytical model for part-load operation of gas microturbines has been elaborated which is subsequently used in the energy and exergy analysis of a sample device. The model, based on the Brayton cycle and heuristic part-load performance formulas, takes into account: the temperature variation of working fluid specific heat at constant pressure in calculations of adiabatic processes, enthalpy, and exergy, the non-linear dependence of pressure drop on flow rate, and the cooling of generator by intake air. The model is validated using the manufacturer data for a commercially available microturbine of 30 kWe and results of measurements. The agreement is very good as for such a general simple analytical model. Exergy calculations based on the elaborated model show that the greatest potential for improving the efficiency of the microturbine lies in the combustion chamber and recuperator, as these components are characterized by the largest exergy destruction and loss.