Designs That Work
Very Cold 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.
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.
Figure 26: Schematic of a Photovoltaic System
Design
Considerations
In the design of photovoltaic systems there are several aspects of the
design that can 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 PV panels should be installed on the South side of the building.
Variations up to 15 degrees of true South will create little change in the
performance of the panels, however, beyond 15 degrees the performance will
begin to decrease. 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 begin to 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 panel temperature, dirt, dust, the resistance
in the wiring 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. Rain tends to primarily perform the cleaning function, but
periodic detergent cleaning can remove any build-up of grime.
The performance of the panels is also significantly 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 Results
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 8.7% of the whole house
energy consumption. |
