Time series analysis of daily horizontal solar radiation

An analysis of the stationary and sequential properties of daily global horizontal solar radiation, on a discrete monthly basis, is presented for a number of locations of widely varying climatic conditions. Such information is essential as input to analytic models for the long-term performance of solar energy systems and for the generation of synthetic daily radiation sequences that can serve as input to numerical simulations that model solar systems. The new aspects of our study include (1) analysis of a solar radiation database that is much larger than those considered heretofore and includes tropical low-latitude, as well as temperate middle-latitude, climates, (2) documentation of the magnitudes and correlations of generalized stationary and sequential radiation statistics for a wide range of climatic stations, (3) proposal of a simple functional form for the probability density function for daily radiation and comparison with actual data, (4) explicit consideration of confidence limits in predicting stationary radiation statistics from a limited number of years of data, (5) evidence that, contrary to the claims of most related studies, there do not seem to be universal values or universal correlations for either the persistence strengths or the persistence times of daily radiation, and, (6) discussion of the practical value of statistical studies of this nature for the design of solar energy systems.