Estimation and Assessment of Direct Normal Irradiance from Meteorological Data: Complete Methodology and Application to Portugal

Engerer model was used to estimate hourly values of direct normal irradiance out of global horizontal irradiance ground measurements for Portugal. Model parameters were calibrated for Évora station (southern Portugal) and applied to a network of 90 stations in mainland Portugal, part of the Instituto Português do Mar e da Atmosfera. From modelled direct normal irradiance time-series, and for stations that comprise 20 years of data, typical meteorological years were determined. A comparison analysis to all stations showed annual availabilities up to ~2307 kWh/m2 in Castro Marim, deviating ~6.81 % from the estimation made by the Photovoltaic Geographical Information System (~2160 kWh/m2). Moreover, to identify locations of interest for possible installations of solar power systems, annual direct normal irradiance availabilities were mapped. This work aims to support decision making at energy policy and management levels by providing reliable estimations of direct normal irradiance.