1. A computer-implemented method for efficiently performing area-to-point conversion of satellite imagery for photovoltaic power generation fleet output estimation, comprising: accessing satellite imagery data of overhead sky clearness for a geographic region suitable for operation of a photovoltaic station; identifying a set of pixels within the satellite imagery data corresponding to a bounded area within the geographic region, each pixel representing collective irradiance over a plurality of points within the bounded area; setting an area clearness index for the bounded area as an average of point clearness indexes derived from the collective irradiance for each point; expressing a variance of the area clearness index as an average of the variance of the point clearness indexes; proportioning the variance of the area clearness index to an area metric corresponding to the physical area covered by each pixel; and determining a variance of the point clearness index for one such point as a ratio of the variance of the area clearness index and the physical area covered by each pixel given the point clearness index for the point, cloud speed, and time interval.