Solar radiation forecasting using zenith angle

This paper discusses simple methods for forecasting solar irradiation. We use the zenith angle (the angle between sun beam and perpendicular line on horizontal surface) to remove both seasonal and time of day effects. Then we forecast by using least-squares (LS), time-varying least squares (TVLS), exponentially weighted recursive least squares (EWRLS) and one step estimation of second order statistics. For comparison we also consider a standard method of normalizing data by subtracting mean and dividing by deviation (at that time of day, sixty days moving average) and then applying the same signal processing algorithms. Finally, we compare simulation results for different sites and various time of prediction. Simulation results shows that using zenith angle in signal processing methods improves the performance.