Functional fuzzy approach for forecasting daily global solar irradiation

A new fuzzy model to forecast daily global solar irradiation at ground level is reported here. The stochastic component of the solar irradiation is mainly determined by the sky condition and it may be quantified by means of the clearness index. Basically the model forecasts daily clearness index, tracking the rules of an autoregressive fuzzy algorithm. Fuzzy c-means clustering is used to establish the membership functions while the overall algorithm is developed in the frame of functional fuzzy systems. A critical assessment of the model performances and limitations is conducted against data recorded at ten European stations, located between 40° and 50° Northern latitude. Based on overall results, it can be concluded that the model accuracy is adequate for routine practical purposes.