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Ultraviolet (UV) total solar irradiation, 290-385 nm (UVT), at ground level in Valladolid, Spain (lat. 41°40′N, long. 4°50′W and 840 m a.s.l.), has been recorded from February 2001 to June 2008. The temporal evolution of the UVT irradiation follows a sinusoidal pattern with maximums in summer and minimums in winter. A complete statistical study of hourly and daily values of UVT solar irradiation has been carried out. The results show that the stability is greater in the summer months and it can be concluded that the maximum values can be considered as representative of UVT irradiation. During an average year, the accumulated UVT solar irradiation is 244.5 MJ m. The relationships between UVT and global solar irradiation have been analysed finding a relationship of 4.2% between them. A potential relationship between both also provides good results. The dependence of UVT solar radiation with solar elevation and cloudiness has been studied. It can be concluded that solar elevation is the main factor to take into account for modelling the UV solar radiation. The dependence of UV/G ratio with cloudiness has been shown introducing the clearness index or global hemispherical transmittance ( k). This ratio has an increasing trend with the cloud cover and hence, it can be deduced that the presence of clouds reduces the global radiation more strongly than the UV component does. UV hemispherical transmittance ( k) has been evaluated. It has been found that k values represent almost 70% of the global hemispherical transmittance in Valladolid city. With a potential relationship between both transmittances coefficient of determination values higher than 0.9 are also achieved. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The article presents a study on the proposed empirical models for ultraviolet total (UVT) radiation. The study uses the measurement of UVT radiation from February 2001 to June 2008 in Valladolid, Spain, the empirical models that lack radiometric variables, and the global radiation measures and parameters of ultraviolet radiation. The study shows that the empirical models had presented that solar elevation cannot determine UV radiation, and the global radiation model elaborated the UVT model.

Abstract: This paper aims at providing scientific evidence of the existence of a high potential of solar energy, not only for the application of flat photovoltaic installations, but also for tracking systems that use concentration, which promise to contribute towards lowering the cost of photovoltaics to the €1/Wp value. It reports results of solar radiation data gathered in Malta (latitude 36°), which represents a central Mediterranean location and compare it to the Region of Valladolid (latitude 42°), within continental Spain to the west of the Mediterranean region. The availability of direct normal radiation is quite good for both sites and could support the building of concentrated systems in the region. A 5-year cumulative annual global solar radiation on a horizontal surface was found to be 1693 and 1841 kWh/m²/day for Valladolid (Spain) and Marsaxlokk (Malta), respectively. Studies showed that Marsaxlokk had a greater normal direct solar potential than Valladolid, but with lower annual variance. Daily analyses showed that Marsaxlokk had more sunny days, similar frequency of partly cloudy days and much lower overcast days than Valladolid. Seasonal analysis showed that Valladolid had less sunshine in autumn and winter but similar availability as Marsaxlokk in spring and summer. A number of correlations between the Clearness Index and the Diffuse Fraction were also made. Such correlations are very useful in estimating past missing data and forecasting future solar availability. [Copyright &y& Elsevier]