Abstract :
Precise aerosol information is indispensable in providing accurate clear sky irradiance forecasts, which is a very important aspect in
solar facility management as well as in solar and conventional power load prediction. In order to demonstrate the need of detailed aerosol
information, direct irradiance derived from Aerosol Robotic Network (AERONET) ground based measurements of aerosol optical
depth (AOD) was compared in a case study over Europe to irradiance calculated using a standard aerosol scenario. The analysis shows
an underestimation of measurement-derived direct irradiance by the scenario-derived direct irradiance for locations in Northern Europe
and an overestimation for the Mediterranean region.
Forecasted AOD of the European Dispersion and Deposition Model (EURAD) system was validated against ground based AERONET
clear sky AOD measurements for the same test period of February 15th to 22nd, 2004. For the time period analyzed, the modelled
AOD forecasts of the EURAD system slightly underestimate ground based AERONET measurements. To quantify the effects of varying
AOD forecast quality in their impact on the application in solar energy industry, measured and forecasted AOD were used to calculate
and compare direct, diffuse, and global irradiance. All other influencing variables (mainly clouds and water vapour) are assumed to be
modelled and measured correctly for this analysis which is dedicated to the specific error introduced by aerosol forecasting. The underestimated
AOD results in a mean overestimation of direct irradiance of +28 W/m2 (+12%), whereas diffuse irradiance is generally underestimated
( 19 W/m2 or 14%). Mean global irradiance values where direct and diffuse irradiance errors compensate each other are very
well represented (on average +9 W/m2 or +2%).
2007 Elsevier Ltd. All rights reserved.
