Probabilistic Solar Irradiation Forecast using Beta Regression

Although renewable energies such as solar and wind power are penetrating rapidly, they require reserve powers for sudden change of output and sometimes cause serious incident in electricity grid because of their unpredictability. On the other hand home energy management systems also need efficient operation of energy storage devices to maximize the utility of facilities including photovoltaics. Therefore to know the uncertainty of their output is crucially important to utilize such unstable power sources effectively. As the solar irradiation has upper and lower bound, beta distribution which has finite interval of 0,1 is suitable to represent the uncertainty of the irradiation. Thus we applied beta regression, which is a kind of generalized linear models using beta distribution, to probabilistic forecast of solar irradiation. As a result of assessment of estimated models by using threat score, precision, and recall, the model employing variable dispersion beta regression showed the best performance in terms of predicting occurrences of large forecast errors. Moreover the precision parameter ϕ(x) of the variable dispersion beta regression was found to be an excellent indicator to alert possibility of large forecast errors.