Directional Solar Variability Analysis

The irradiance at ground level mostly fluctuates due to cloud coverage. As clouds are moving toward a certain direction, the cardinal orientation of photovoltaic arrays affects the variability of the output power, and thus the impact on the electric power grid. This paper presents a new methodology with a circular layout for irradiance monitoring units to assess the solar variability in different directions of any site based on cloud speed-direction trend and directional variability reduction. The proposed methodology is used to assess the directional variability for a site at Varennes, QC, Canada using 1 year of measured data. The cloud speed direction is studied in order to observe any trend from a month-to-month and from an hour-to-hour. Overall the cloud direction has a trend of West to East direction, especially during the winter months. The variability reduction for each axis is estimated using the variability index (VI). The largest VI reduction is observed close to the cloud direction axis.