Correlation of actual efficiency of photovoltaic panels with air mass

Photovoltaic installations are already producing more than 5% of electricity in several European countries. Monitoring of photovoltaic parks produces a huge amount of data that are employed in checking the real-world efficiency of photovoltaic panels in a variety of locations, for different atmospheric and environmental conditions. The aim of this paper is to present real-world efficiency data for photovoltaic panels and photovoltaic parks, as function of air mass and environmental conditions. The PV efficiency deteriorates quickly when the solar altitude is less than 45° and the solar insolation drops below 200 W/m2. This affects the accuracy of prediction of overall efficiency of PV parks and deserves more attention and study.