  Amongst all the renewable energy resources (RES), solar is the most popular
form of energy source and is of particular interest for its widely integration
into the power grid. However, due to the intermittent nature of solar source,
it is of the greatest significance to forecast solar irradiance to ensure
uninterrupted and reliable power supply to serve the energy demand. There are
several approaches to perform solar irradiance forecasting, for instance
satellite-based methods, sky image-based methods, machine learning-based
methods, and numerical weather prediction-based methods. In this paper, we
present a review on short-term intra-hour solar prediction techniques known as
nowcasting methods using sky images. Along with this, we also report and
discuss which sky image features are significant for the nowcasting methods.
