Comparison of solar radiation in Marsaxlokk, Malta and Valladolid, Spain

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.