The purpose of this paper was to evaluate forecast accuracy by using data of primary production of electricity in Slovakia. It is therefore aimed to analyse SES forecasting method. To estimate optimal value of smoothing constant, forecasts are computed with a = 0:1 to a = 0:9, with increments of 0.01. Three forecasting accuracy techniques, such as MAE, MAPE, and RMSE are used to select the most accurate forecast for one year ahead forecast.