Net ZEB Case Studies - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 371

energy use was reduced by 7%. This is a positive outcome, since it indicates
that the designers of ÉcoTerra did not miss any major opportunities. In
order to attempt to offset all energy use with renewable energy, the gap
should be filled with the energy supply side.
Fig. 7.20 Electricity use and generation for successive upgrades
For active solar energy collection, an existing issue that should be
considered is snow accumulation on the roof and its negative impact on
wintertime generation. For example, the performance in 2010 clearly
indicates that the performance in the winter fell short of theoretical
performance ( Figure 7.14 ) . Thus, the effect of increasing the BIPV/T roof
slope to 45° (from 30°) was examined. From experience, this slope has been
found to effectively shed snow (Athienitis, 2007). RETScreen (RETScreen
International, 2005) indicates that the difference in slope has a minor effect
on annual incident solar radiation, since both slopes are in the near-optimal
range for the site's latitude - 45°N. Assuming that the base of the
south-facing roof remains the same, the additional pitch results in a 22%
increase in area for a total surface area of 65.6 m 2 .