Estimation of economic efficiency of launching an autonomous natural gas power plant in comparison with the purchase of electric power from the power system is presented. A method for assessing the accumulated discounted effect is proposed. A regression model for the dependence of the efficiency of eigen electric generation on external and internal factors is constructed. The equation of the surface dividing the space of independent variables into economically viable and unprofitable combinations from the view point of using an autonomous electric power source is derived. The effect of individual factors on the considered economic efficiency is determined. The largest positive impact of the electricity price and installed capacity utilization factor on the value of the economic effect is shown. The average prices for purchased natural gas and electricity in Russia observed for the last 6 years are shown to locate near the dividing surface.