Total global solar shortwave (G) irradiation and sunshine duration were recorded at nine Spanish stations located in the Iberian Peninsula. G irradiation under cloudless conditions was simulated by means of a radiative transfer model using satellite data as input. A method based on these cloudless simulations and sunshine duration records was developed to reconstruct G series. This model was validated against experimental data, providing a good agreement for cloudless skies (mean bias error of 0.4% and root mean square error of 5.8%). Monthly averages of modelled and measured G irradiation presented a mean bias error of 0.5% and a root mean square error of 3%. Differences between modelled and measured G irradiation were in agreement within the model uncertainties. The reconstruction model was applied to sunshine duration measurements, giving long-term G series at the nine locations. Monthly, seasonal, and annual G anomalies were calculated and analysed. Averaged series (using the nine locations) showed a statistically significant decrease in annual G from 1950 to the mid 1980s (−1.7%dc−1) together with a significant increase from the mid 1980s to 2011 (1.6%dc−1). The effect of uncertainty in the reconstructed series on statistically significant trends was studied.