A net zero source energy building produces as much en- ergy as it uses compared to the energy content at the energy source. The system boundary is drawn around the building, the transmission system, the power plant, and the energy required get-
ting the fuel source to the power
plant. It tends to be a better repre-
sentation of the total energy impact.
However, it is challenged by dif-
ficulties in acquiring site-to-source
conversions and by the limitations
of these conversions. Fixed con-
version factors do not account for
dispatch of energy with time of day,
and the changes in dispatch as new
buildings and the new power plants
to supply them come on-line. This
definition can depend on how the
utility is buying or producing the
power, rather than on the energy
performance of the building. So,
if someone wants to construct a
building in an area with a large per-
centage of hydroelectric energy, it
may have a low source energy impact. However, placing the building in that location may necessitate new fossil fuel generation plants and the building may actually use the new generation capacity, which is coal. This analysis is very difficult.