ARTICLE IN PRESS2852F.R. Mart<strong>in</strong>s et al. / Energy Policy 36 (2008) 2843–2854Fig. 8. (a) Annual average of daily sum of the diffuse solar irradiation <strong>in</strong> <strong>Brazil</strong>ian territory. (b) Seasonal averages of daily sum of the diffuse irradiation <strong>in</strong> <strong>Brazil</strong>ian territory.The seasons are arranged as described <strong>in</strong> Fig. 3.
ARTICLE IN PRESSF.R. Mart<strong>in</strong>s et al. / Energy Policy 36 (2008) 2843–2854 2853w<strong>in</strong>ter). One hypothesis may be the <strong>in</strong>crease of aerosol particlenumber concentrations emitted to the atmosphere by the burn<strong>in</strong>gof biomass typical dur<strong>in</strong>g this time of the year <strong>in</strong> these regions.3.3. <strong>Solar</strong> irradiation over a tilted planFig. 7 presents the maps for annual and seasonal means ofglobal solar irradiation over a plan tilted to an angle equal to thecell latitude. The assessment of the ‘‘tilted’’ comp<strong>one</strong>nt is veryimportant <strong>in</strong>formation for the development of PV applications andsolar heat<strong>in</strong>g systems. Disregard<strong>in</strong>g the local topography, the solarirradiation over a surface tilted to a latitude angle is theconfiguration that allows captur<strong>in</strong>g the maximum solar <strong>energy</strong>throughout 1 year.All maps <strong>in</strong> Fig. 7 present similar patterns as discussed forglobal solar irradiation. The furthermost levels of irradiation onthe tilted plane occur <strong>in</strong> the range that goes from the Northeast tothe Southwest dur<strong>in</strong>g the spr<strong>in</strong>g and the smallest values <strong>in</strong> all<strong>Brazil</strong>ian regions occur dur<strong>in</strong>g the w<strong>in</strong>ter months.3.4. Diffuse solar irradiationFig. 8 exhibits the maps for annual and seasonal averages of thedaily total of diffuse solar irradiation. On the annual average <strong>one</strong>can observe that the Northern region receives greater diffuseirradiation ma<strong>in</strong>ly <strong>in</strong> the estuary of the Amazon River. This is dueto the larger nebulosity <strong>in</strong> the region as a result of the ITCZ<strong>in</strong>fluence. Seasonally the greatest diffuse irradiation occurs dur<strong>in</strong>gthe summer throughout the Amazon region. The smallest valueshappen dur<strong>in</strong>g the dry season (fall and w<strong>in</strong>ter) <strong>in</strong> the Southeasternand Southern regions.4. ConclusionsThis paper describes the satellite-derived assessment of solar<strong>energy</strong> resource prepared dur<strong>in</strong>g the SWERA project. The projectSWERA had f<strong>in</strong>ancial support from UNEP and GEF and it aimed atprovid<strong>in</strong>g reliable and high-quality <strong>in</strong>formation to decisionmakers, politicians, <strong>in</strong>vestors and stakeholders <strong>in</strong> order to fosterclean <strong>energy</strong> applications <strong>in</strong> develop<strong>in</strong>g countries. The solarirradiation maps for <strong>Brazil</strong> were prepared by us<strong>in</strong>g a radiativetransfer model BRASIL-SR fed by climate data and satellitederivedcloud cover data. The reliability of solar resourceestimates and model BRASIL-SR performance were checked outthrough comparisons with solar estimates provided by numericalmodels adopted <strong>in</strong> SWERA to map solar resources <strong>in</strong> otherparticipat<strong>in</strong>g countries and comparison with ground data acquired<strong>in</strong> all <strong>Brazil</strong>ian regions. Concisely, the model BRASIL-SRpresented a similar performance as other core models adopted bythe SWERA project for solar assessment <strong>in</strong> other regions, but itusually overestimates solar irradiation—MBE around 6% andRMSE about 13%.The larger values of global solar irradiation were found for thesemi-arid area <strong>in</strong> the <strong>Brazil</strong>ian Northeast region. The extremelydry environment (semi-desertic) and the high number of sunsh<strong>in</strong>ehours all year round resulted <strong>in</strong> mean solar irradiation around6.5 kWh/m 2 day. Slight smaller values were obta<strong>in</strong>ed for theSouthern region dur<strong>in</strong>g spr<strong>in</strong>g and summer seasons. However,the solar irradiation there presents higher variability through theyear due to the <strong>in</strong>cursions of cold fronts orig<strong>in</strong>at<strong>in</strong>g from the deepcyclonic systems <strong>in</strong> the Antarctic region, ma<strong>in</strong>ly dur<strong>in</strong>g fall andw<strong>in</strong>ter seasons.The maps for solar irradiation over a plane tilted <strong>in</strong> a angleequal to the local latitude po<strong>in</strong>t toward the great potentialavailable for solar <strong>energy</strong> applications <strong>in</strong> <strong>Brazil</strong>, even <strong>in</strong> the semitemperateclimate <strong>in</strong> the Southern region where annual mean ofsolar irradiation is comparable to that estimated for the equatorialAmazonian region. It was also verified that all <strong>Brazil</strong>ian territoriesreceive larger solar irradiance than many of the Europeancountries where a large number of solar <strong>energy</strong> projects are be<strong>in</strong>gimplemented ma<strong>in</strong>ly as a result of good <strong>energy</strong> regulation forrenewables and valuable government <strong>in</strong>centives.The <strong>scenarios</strong> for solar thermal and PV applications, preparedby us<strong>in</strong>g the GIS database acquired dur<strong>in</strong>g SWERA together withthe solar resource maps presented here, will be discussed <strong>in</strong> twoother papers to be published <strong>in</strong> the near future.AcknowledgmentsThis work was possible thanks to the f<strong>in</strong>ancial support ofUNEP/GEF (GFL-232827214364–SWERA) and FINEP(22.01.0569.00). This work was prepared with the fundamentalcontribution of the follow<strong>in</strong>g colleagues: Silvia V. Pereira, Crist<strong>in</strong>aYamashita, Sheila A.B. Silva, Hugo Corrá and Rafael Chagas. Thefollow<strong>in</strong>g <strong>in</strong>stitutional acknowledgment is due to Centre forWeather Forecast and Climatic Studies (CPTEC) and, <strong>in</strong> particular,for the people from the Environmental Satellite Division (CPTEC-DSA) for the cont<strong>in</strong>uous support <strong>in</strong> satellite data and ancillarysatellite products and from the Laboratory of MeteorologicalInstrumentation (CPTEC-LIM) for the support <strong>in</strong> operation andma<strong>in</strong>tenance of ground measurement sites. Thanks are due toDave Renné (NREL/USA), Richard Perez (SUNY/Albany) and TomHaml<strong>in</strong> (UNEP) for help and scientific contributions to thedevelopment of the SWERA project. 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