faces, which may not be the optimal angle to the sun. This issue often results
in lower power collection.
Ballasted-mount systems are sensitive to wind speeds. They do not allow for
much airflow, which may range from fair to poor, but are a solution for
flat roofs.
Tracking-mount systems provide the best situation for the cell to collect
sunlight. They allow for fair to good airflow. However, they are costly and
require routine maintenance.
In BIPV applications where solar roof tiles are mounted in place of tiles on a
standard roof, airflow will drop from poor to bad. However, an aggressive
design that allows for three or more inches of airflow will improve the
situation. Even large battens will not allow for enough airflow to get out of
the bad range, though.
BIPV wall units also have very poor airflow unless creatively designed.
BIPV with open roof underside and clear airflow, as in a parking structure,
canopy, patio, or breezeway, have fair to good airflow and potentially even
very good, on some applications.
Unfortunately, airflow is rarely considered in design, but its effect on perfor-
mance and system life cannot be ignored.
BIPV Applications
Building-integrated PV (BIPV) systems are electric generating systems integrated
into the shell of the building or other structure. The PV component takes the
place of traditional building materials or components. Shingles, overhangs, cano-
pies, parking structures, skylights, and windows are all potential BIPV applica-
tions. Advantages to BIPV systems over standard options are:
Some BIPV products are made to interface with the building structure and
do not always require additional racking components. A glazing product is a
good example.
Some provide day lighting, shading, insulation, sound control, thermal
collection, and wind protection, all while producing electricity.
Costs are higher with BIPV systems, but those costs are often offset by the
fact that BIPV systems replace other building materials. Many times no
additional construction materials are needed to mount them.
Electricity savings over time displace the initial cost of the system in
residential and commercial applications. In this instance, the BIVP product
pays for itself one or more times with energy production and savings.
BIPV products are often appealing to the eye and increase the positive
visibility and educational impact of solar power.
CHAPTER 9 PV System Mechanical Design 173

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