Abstract Ephemeral clouds and atmospheric aerosols pose the greatest challenges in exploiting sunlight as a viable (both stable and reliable) source of energy. The passage of cloud shadows across a solar array results in significant fluctuations, or ramps, in available energy, while scattering aerosols redistribute direct and diffuse components of solar irradiance in a subtle but pervasive and more sustained way. The timescales of these fluctuations are highly diverse, varying from seconds, in the case of fair-weather cumulus clouds, to hours, in the case of a prefrontal cirrus shield, and to days or more in association with aerosol loading within a synoptic-scale air mass. The spectrum of spatial scale for aerosol and cloud parameters is broad, and monitoring from terrestrially based systems is an inherently ill-posed problem from the standpoints of cost and coverage. Here, satellite-based observations, particularly those from geostationary platforms capable of monitoring the temporal evolution of clouds, provide unique and indispensable capabilities with regard to solar-energy forecasting and resource assessment. In this chapter, we provide a high-level cross-section of environmental satellite observing systems and considerations for their application to quantitative, physically based estimates of solar irradiance at the surface for use in solar forecasting.