High resolution direct normal irradiance data for testing CPV plants: ISFOC database

Abstract

Knowledge about hourly solar radiation in terms of intensity and time distribution is essential for the design of solar energy systems. Accurate forecasting of solar radiation over a limited area is needed in order to estimate the available energy as a source of electricity. The increasing interest in Concentrated-Photovoltaic Energy (CPV) as an incipient solar renewable energy demands high quality measurements of Direct Normal rradiance (DNI). The probabilistic properties of the hourly DNI are analyzed over one-year database once the data estimated by analytical models and compared with observations. Diffuse Fraction correlation index, Kd, derived from clearness index, Kt, appears as a tool for predicting hourly DNI from hourly Global Irradiance. A correct interpretation of DNI variations in time is presented in this work as an indispensable previous step for short-range forecasting of the solar energy available for CPV power plants in order to assess the concentrated solar module-tracking systems performance. © 2010 American Institute of Physics.