Estimating Solar Irradiance Using Sky Imagers.

Ground-based whole sky cameras are now-a-days extensively used for localized monitoring of the clouds. They capture hemispherical images of the sky at regular intervals using a fisheye lens. In this paper, we derive a model for estimating the solar irradiance using pictures taken by those imagers. Unlike pyranometers, these sky images contain information about the cloud coverage and can be used to derive cloud movement. An accurate estimation of the solar irradiance using solely those images is thus a first step towards short-term solar energy generation forecasting, as cloud movement can also be derived from them. We derive and validate our model using pyranometers co-located with our whole sky imagers. We achieve a root mean square error of 178 Watt/m² between estimated and measured solar irradiance, outperforming state-of-the-art methods using other weather instruments. Our method shows a significant improvement in estimating strong short-term variations. [ABSTRACT FROM AUTHOR]