Cumulative frequency distributions of daily clearness index for temperate and high latitudes

Abstract

Cumulative distributions of daily clearness index, which is based on actinometrical observations from meteorological stations and NASA POWER data, have been constructed for the Russian Federation territory, which spans a wide range of latitudes and covers more than half of the high-latitude Northern Hemisphere. Possible applications of NASA POWER data for the simulation of solar power systems at temperate and high latitude areas have been shown. Daily clearness index distributions were approximated by equations derived from data in tropical climate conditions, with modified dimensionless variables. These equations were found to be adequate for high latitudes, which provides greater confidence that they are universal. It has also been shown here that the selection of the extra-terrestrial radiation calculation method has an influence on the calculated clearness index value, especially for high latitudes. The difference between Cooper's equation for declination and calculations conducted with NASA POWER data at high latitudes is more than 35%.