Assessing Electrical Demand in New Buildings
For new buildings, assessing electrical demand is
harder to determine. Some PV installers will use
energy modeling or will attempt an energy model
comparison with other buildings with nearly
identical electrical loads based on size and
location.
Shade Types
Ideally, PV modules should be installed in shade-
free locations. Shading reduces the output of the
PV system, and often a small amount of shading
will lower PV system output more than expected.
Shading is possible no matter where an array is
placed. It can be small amounts of shading from
leaves and bird droppings. Or it can be the result
of a new building eclipsing the array. Energy
output is severely diminished by even min-
imal shading.
The amount of shading at a PV site greatly
influences the module connection method. In an
ideal world, without shading, energy production
does not hinge on the PV array connection arrangement. Taking that into
account, string inverters are simple and cheap to install. For the majority of PV
systems, parallel connections are the smart option but are more costly to install.
However, studies have shown that in the long-term calculation, parallel connec-
tions have a 30 percent higher power production than series connections.
The impact of shading hinges on certain considerations:
Sum of shaded modules
Interconnection between PV cell and bypass diode
Amount of shading
Path of shading over time
PV module interconnection process
Design of the inverter
There are several things about shading that PV installers need to know. The
solar path changes throughout the day and throughout the year. It is important
to consider how shading may change throughout the year using a shading
analysis.
There are five different types of shading that you will encounter when con-
ducting shading analysis. The first type is called temporary shading. Temporary
NREL engineer James Salasovich checks a shade analysis
tool. In this instance, the device used is a SunEye. The
SunEye analyzes shade to help determine a site’s solar
energy potential.
Courtesy of DOE/NREL, Credit: Patrick Corkery
72 ADVANCED PHOTOVOLTAIC INSTALLATIONS
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