Data of the time series of the daily solar irradiation on horizontal surfaces from 32 Spanish stations were analyzed. The method applied deals with stochastic components X(i,t) as following a first order Markov model. The results of the first order autocorrelation coefficient for each series vary from 0.23 to 0.49 in the Peninsula and from 0.33 to 0.62 in the Islands. The similitude, based on a contingency coefficient, between the frequency distributions of the simulated and experimental data of the residual time series X(i,t), is about 90% for every station.