Designs That Work
Hot-Humid Climate
Advanced Technologies - Photovoltaic Panels
Photovoltaic (PV) Panels are used as a means to generate on site
energy. The panels are relatively easy to integrate into the design of the
house and power system, and are a means to reduce source energy
consumption. One of the draw backs are that at this point in time is that
the cost of PV panels, while lower than a few years ago, still does not
make them cost effective from a payback point of view. The amount of
energy generated takes many years to pay off the initial cost of the
panels. However, as the use and demand for PV technology increases and
further advances in the technology increase the performance of the panels,
the costs will continue to drop, making the technology more viable
financially.
Figure 32: Schematic of a Photovoltaic System Design Considerations
Photovoltaic systems require a collector panel and an inverter in order
to produce electricity that is able to be used by the home. Photovoltaic
systems are either connected to a battery storage system located on site,
or connected into the power grid of the community. For locations where
connection to a power grid is not available or impractical, then a battery
storage system is desirable. Battery storage systems however, do require
maintenance to ensure that they continue to function adequately. Tying
into the local power grid is generally recommended over battery storage
when possible, due to the simplicity and costs. This removes the concerns
with maintenance of the battery systems.
Design Considerations
There are several aspects of the design of photovoltaic systems that
can significantly affect the performance of the system. The location and
angle of the collector, internal losses, shading, and temperature should
all be considered in the design of the system.
The collector plate should be installed on the South side of the
building. Variations within 15 degrees of true South will create
relatively little change in the performance of the panels, however, beyond
15 degrees the performance starts to drop off significantly. Also, setting
the tilt of the panel to maximize the summer time solar incident angle can
increase the energy production of the panel over the course of the year.
This can be more difficult than it seems as aesthetic issues often come
into play. It may not always be desirable to have the panel in a location
of high visibility, and architectural design may limit the options for the
collector tilt angle. If PV technologies are going to be incorporated into
the design, it should be considered early on in the conceptual design
stage, so that systems could be properly integrated into the aesthetic
design of the building.
Most systems will experience some internal losses in the system, and
only reach approximately 80% to 90% of the rated output of the panel at a
maximum. The losses are from dirt, dust, the resistance in the wiring,
elevated temperature of the panels, and losses through the inverter. This
is common for most systems and should be accounted for in the design of
the system.
Even the least bit of shading of the panels can dramatically decrease
the performance and close attention to keeping the panels in direct
sunlight is very important. This is due to the way the photosensitive
cells are linked in the array. Therefore it is very important that the
panels are placed in a location such that surrounding elements (such as
trees and chimneys) do not cast a shadow over even a portion of the panel.
Ideally, the panels would also be cleaned with some regularity of dust,
leaves, snow, or any other matter that might get deposited on the solar
collector.
The performance of the panels is also affected by temperature. As the
temperature of the panel increases, the output of the panels is reduced.
Therefore it is important to try to keep the panels as cool as
possible. One strategy is to install the panels slightly off the surface
of the roof, to allow for some ventilation behind the panel.
Energy Model
The system used in the energy model is based on a 1.9 kW photovoltaic
system (Similar to SunWize Packaged PV system including a Sanyo 190BA3
Solar Module and a Fronius Grid-Tie Inverter). The area of panels required
for this system was equivalent to 127 square feet or 10 panels. The amount
of site generated energy was able to make up 13.9% of the whole house
energy consumption. |
