Even where reasonably accurate annual average values are used, they do not reflect the variations in building operation in response to weather and over the course of the day, week, and year. Furthermore, the electric grid itself has large temporal variations by hour, day of the week, and season. Different plants are on-line as "baseload" and are always on and http://excavations.comuv.com others come on as needed. In some locations, the baseload generation is relatively "clean" (hydro and nuclear), and the peak load is relatively dirty (coal). In other locations it is exactly the opposite. Wind, solar, geothermal, and gas also play their roles to varying degrees.
