Deriving Solar Radiation in a Mountain Area from MODIS Information

Abstract

Solar radiation has a direct influence on the air and ground temperature, indirect influence on the value of atmospheric humidity, movement of air masses and precipitations, and it is easy to understand how its evaluation is essential not only in the technological area such as for sizing solar heating and photovoltaic plants, but also in fields such as agriculture or meteorology. Nowadays, the assessment of the solar energy resources over large areas and the elaboration of solar radiation maps are conducted using satellite derived information. Among the existing methodologies, those based on parametric models to firstly estimate the clear-sky solar radiation are usual. The success of that option depends both on the accuracy of the solar radiation algorithm and the satellite derived information and on the relationship between each other.In this work, daily global solar irradiation under clear skies is estimated by means of a model which includes the horizon effects. This characteristic is important in those cases where a complex topography is present, such as mountains. The topographic information is obtained from a digital elevation model. The other inputs to the model are the atmospheric precipitable water vapour content, the Angström's turbidity coefficient and the ground albedo. Experimental values of the atmospheric precipitable water vapour content are obtained from the MODIS sensor. The two latter parameters are averaged values calculated on previous studies.Estimates by the model are compared with ground measurements obtained in fourteen radiometric stations located in a mountain zone (Sierra Nevada, Granada, Spain) recording global solar radiation, atmospheric temperature and relative humidity. Since ground experimental values of precipitable water vapour content are available, a comparison between these values and those derived from the MODIS sensor is also presented.