Solar Power in Building Design
Author:
Peter Gevorkian, Ph.D., P.E.,
ASIN: B00121SIIM
Publisher: McGraw-Hill
Professional
Shading Analysis and Solar Energy
Performance Multiplier
One of the significant steps prior to designing a solar power is to
investigate the location of the solar installation platform where the solar
PV arrays will be located. In order to harvest the maximum amount of solar
energy, theoretically all panels in addition to being mounted at the optimum
tilt angle must be totally exposed to sun rays without any shading that may
be cast by surrounding building, object, trees, or vegetation.
To achieve the preceding objective, the solar power mounting terrain or the
platform must be analyzed for year-round shading. Note that the casting of
shadows due to the seasonal rise and fall of the solar angle must be taken
into account as it has a significant impact on the shadow direction and
surface area. For instance, a shadow cast by a building or tree will vary
from month to month changing in length, width, and shape.
In order to analyze yearly shading of a solar platform, solar power
designers and integrators make use of a commercial shading analysis
instrument called the Solar Pathfinder shown in Figure 4.6. The Solar
Pathfinder is used for shade analysis in areas that are surrounded by
trees, buildings, and other objects that could cast shadows on a designated solar platform. The device is essentially comprised of a semispherical plastic dome shown in Figure 4.7, and
latitude-specific yearly solar intensity time
interval semicircular removable or disposable plates shown in Figure 4.8.
Figure 4.9 represents latitude map of the United states.
The disposable semicircular plates shown in Figure 4.8 have 12-month
imprinted curvatures that show percentage daily solar energy intensity from
sunrise (around 5 a.m.) to sunset (around 7 p.m.). Each of the solar energy
intensity curves from January to December is demarcated with vertical
latitude lines denoting the separation of daily hours. A percentage number
ranging from 1 to 8 percent is placed between adjacent hourly latitude
lines.
Percentage values progress upward at sunrise from a value of 1 percent to a
maximum value of 8 percent during midday at 12:00 p.m. and then drop down to
1 percent at sunset. Depending on the inclination angle of the sun, the
percentage solar energy values depicted on the monthly curvatures vary for
each month. For instance, the maximum percentage value for the months of
November, December, and January is 8 percent at solar noon 12:00 p.m. and
for the other months from February through October the percentage value is 7
percent.
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