TAG: A time-dependent, autoregressive, Gaussian model for generating synthetic hourly radiation

Abstract

A model is described which generates synthetic daily sequences of hourly radiation values, on the horizontal plane, for any location, with the daily clearness index K t as input. The model assumes that for each K t and solar hour the probability density of the hourly clearness index k t is (simply) a truncated Gaussian function. A first-order autoregressive model is fitted for the k t variable, normalised using parametrisations for the time-dependent average and standard deviation values. Values generated by this ARMA (1,0) model can then be transformed backwards to generate synthetic sequances of k t values. Using a diffuse fraction correlation and a tilted radiation model, the horizontal global data can be transformed to any desired plane, thus providing solar system designers with the necessary hourly data for the accurate sizing of every type of solar system, including stand-alone, high solar fraction and passive ones.