Short-Term Intermittency of Solar Irradiance in Southern Norway

Abstract

The temporal variability of solar irradiance at small time scales ranging from 1 second to 2 minutes was studied to characterize the short term fluctuations in irradiance at high latitudes. The change in irradiance at time scales of 1, 5, 10, 30, 60 and 120 seconds were calculated from irradiance data measured at a test station in Grimstad, Norway, over a one year period. The number of occurrences of different ramps in irradiance was analyzed at different time scales. The largest change in irradiance was detected over a 2 minute time interval with an amplitude of 995 W/m2. Similar amplitudes were detected at time intervals of 30 and 60 seconds. However, such large changes (above 900 W/m2) occur only a very few times over a year. The distributions of irradiance fluctuations at different time scales show that although, large changes in the range of above 600 W/m2 occur at time scale of 1 s, the number of occurrences over a year is significantly smaller than the number of occurrences at time scales above 5 s. Further, the number of occurrences of high magnitude fluctuations over a year particularly in the range of 500 W/m2 – 900 W/m2 does not show significant dependence on the time scale for time scales above 5 s.