| Criterion
6.5.13
Shading of Collector
Criteria
text:
The
location and orientation of the collector shall be such that it
is not shaded by external obstructions or mutual shadowing more
than the specified period allowed in the design.
Comments:
This requirement is quite self-explanatory and is one of the
first things an installer determines prior to system installation.
Collectors should be installed in a unobstructed location, preferably
with no shading on the array between 9 am and 3 pm (at a minimum)
solar time, at any time of the year. Figure 1 indicates that this
site should have no problems with shading. Nevertheless, there
are situations in which how much solar access is available and
where to place the collector can be questionable.
Figure 1
For
example, a roof mounted air conditioning unit (Figure 2), roof
wings (Figure 3), false fronts (Figure 4), chimneys, etc., may
be adjacent to the solar collector and could affect solar access
and shading.
Figure 2
Figure 3
Figure 4
In
other situations, natural elements such as trees and large vegetation
can obstruct solar access during certain times of the day and
year. See Figure 5 for a site that has an easily identifiable
problem. The house roof faces north and south. The trees create
shade on the south facing roof.
Figure 5
Keep
in mind that the sun is lower in the horizon in the winter. Take
careful note of potential shade problems in the horizon as these
may be affected by seasonal sun positions. As indicated in Figure
6, what appears to be an unshaded site during the summer may be
otherwise during the winter months.
Figure
6
Although
most experienced installers have a good eye for solar access,
there are times when the use of a solar pathfinder (Figure 7 and
8) can be of immense assistance when solar access is questionable.
(Please note that the site selector indicated in Figure 8 is no
longer available. It is shown here for educational purposes.)
The solar pathfinder is a very easy device to use and will help
determine shading problems throughout the course of a day as well
as seasonally. Once again, the objective is to identify a location
that is un shaded between the hours of 9 a.m. and 3 p.m. (at a
minimum) solar time throughout the year. If need be, the installer
can adjust the collector location or eliminate shading concerns
to obtain an unobstructed solar window for the collector.
Figure
7
Figure
8
A
template (Figure 9) in this particular solar pathfinder device
allows the installer to determine and record the shade that will
occur at a specific location.
Figure 9
Care
must be taken to use the solar pathfinder at the location where
the collector will be installed. Figure 10 below indicates that
there can be a great difference between whether the collector
is installed on a roof versus at ground level.
Figure
10
As shown in Figures 11-12 below, the use of the solar site selector
indicated in Figure 8 also allows the installer to determine and
record the shade that will occur at a specific location. Note
that in Figure 11 the site selector indicates that there will
be no obstructions during the course of the day, while in Figure
12, it is quite evident that shading will occur in the morning
hours.
Figure
11
Site 12
Additional
information on the solar pathfinder indicated in Figure 7 above
can be obtained at: http://www.solarpathfinder.com/
The
solar site selector shown in Figure 8 above appears to no longer
be available.
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