Hi, I'm a student doing a project that involves building a model house with passive solar heating system. I'm curious if there is a way to approximate the amount of heat I will absorb through a south facing window on a sunny day, in early April. I realize this depends on many variables, but I'm just looking for a ball park figure (10 BTUs, a billion BTUs?) I'm in Boulder Colorado (North Latitude 40 degrees). The average high is about 55F. Anyone have any thoughts? Thanks!