Solar Irradiance Modeling over Indian Sub-continent using Cloud Microphysical Properties from INSAT-3DR

The extraterrestrial radiation that the earth receives at the top-of-atmosphere is a function of earth-sun distance. For a given location on the earth the TOA irradiance, varies along the day and throughout the year. Clouds, atmospheric particles, or bright ground surfaces such as water bodies, ice and snow reflect about 29% of the solar energy that arrives at the top of the atmosphere back to the space. Approximately 23% of incoming solar energy is absorbed by water vapour, dust, and ozone, and 48% passes through the atmosphere and is absorbed by the surface. The purpose of the current study is to model the solar irradiance reaching the earth's surface attenuated by the gases, aerosols, and clouds present in the atmosphere for the Indian sub-continent implementing the geostationary satellite INSAT-3DR. The radiative transfer models incorporate the multiple scattering and absorption phenomenon occurring within the atmosphere, and between surface and atmosphere considering plane-parallel or pseudo-spherical geometry. In this study, we implement the Fast All-sky Radiation Model for Solar applications (FARMS) to compute the direct normal irradiance (DNI), diffuse horizontal irradiance (DHI), and global horizontal irradiance (GHI) in presence of clouds. The clear-sky transmittance are first estimated from REST2 with inputs of aerosol optical depth and concentration of gases in the atmosphere. FARMS requires cloud parameters of cloud optical thickness, cloud effective radius, and cloud type. We utilize cloud information retrieved from geostationary satellite INSAT-3DR to be used as inputs to the model. The cloud optical thickness and cloud effective radius are obtained at the nominal wavelength of 0.65 m. We design an algorithm to approximate the cloud type from the brightness temperature data. The brightness temperature is a representation of cloud top temperature under defined conditions of cloud phase (water, ice, or mixed). The aren't any all-sky radiative transfer models that takes designated inputs from Indian geostationary satellites. The irradiance computed in the study are at half-hourly temporal resolution and valid for 3-5 km spatially. The data is useful for 15 min to a week ahead forecasting of solar irradiance, which is required for solar plants in operations and energy load assessment.