In this work, a numerical method, based on the one-dimensional finite difference technique, is proposed
for the approximation of the heat rate curve, which can be applied for power plants in which no data
acquisition is available. Unlike other methods in which three or more data points are required for the
approximation of the heat rate curve, the proposed method can be applied when the heat rate curve data is available only at the maximum and minimum operating capacities of the power plant. The method is applied on a given power system, in which we calculate the electricity cost using the CAPSE (computer aided power economics) algorithm. Comparisons are made when the least squares method is used. The results indicate that the proposed method give accurate results.