1. A method for predicting an output of a photovoltaic (PV) device, comprising the steps of: applying Fourier analysis to data to obtain frequencies and a mean of the frequencies in the data, wherein the data are time series of a historical outputs of the PV device; applying regression analysis to the data to obtain a regression coefficient; and predicting the PV output at a time step by summing the mean at the time step and a deviation from the mean at a previous time step, wherein the means are approximated by selected frequencies, and, wherein the deviation for the previous time step is weighted by the regression coefficient, and wherein the steps of the method are performed in a processor.