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Photovoltaic Design |
Roof Mounts
Roof mounts are the most popular choice for small residential systems. The
modules are located above most objects that would cause shading problems and
the large roof surface makes it easy to attach the mounting structure. A roof
mount also locates the modules out of the way and out of sight, reducing the
possibility of vandalism or theft. If your roof is facing in the wrong
direction or the roof pitch causes problems then modules can be installed on a
south facing wall using the same mounting structure. Roof mounts may also be
secured to the ground.
Pole Mounts
Pole mounts are easy to install and allow the array angle to be adjusted after
installation. The mounting frame fits on a length of schedule 40 pipe
(available locally at any metal shop) set securely in a concrete form in the
ground. Whichever mounting structure is chosen air circulation and snow load
must be considered.
Air Circulation
All PV mounting structures must have good air circulation around the modules.
Air circulation provides natural cooling of the modules and increases
efficiency by allowing them to operate at lower temperatures. If the site where
your array will be mounted receives high winds you must ensure the back of the
modules are not exposed. High winds and northerly winds during the winter can
create uplifting forces strong enough to seriously damage your array. Spacing
your modules a few inches apart decreases the likelihood your array will be
damaged by the wind.
Snow
In regions with heavy snowfall an array should be installed where snow can be
easily brushed off. A pole mount allows snow to slide off easily. If modules
are tilted at an angle of 45É or more then a few sunny days will usually melt
snow off the array.
Maximum Power Output
To achieve the best performance from your array it should be aimed in the
direction of most sunlight and angled correctly for the season. The array
should be adjusted to the latitude plus or minus 15É from summer to winter for
optimal output. If your mounting structure is not seasonally adjustable the
modules should be mounted to achieve maximum output during the period of
highest usage. For example, if you use your cottage during the summer months
your array should be mounted accordingly.
PV modules should always be aimed in the direction where they receive full exposure to sunlight. In areas with little or no shading, modules should face south. However, magnetic south on a compass may not be an accurate indicator of true south. Consulting a good map of your area usually indicates the correction factor to adjust compass readings.
Most of the sun's power occurs between 10 am and 2 pm. If your array receives full exposure during these hours then adjusting your array is unnecessary. If your array is significantly shaded during these hours then you should position your array at the midpoint of the sunny period. For example, if your array received full exposure from 7 am to 1 pm then it should be positioned to face the sun at 10 am.
In some locations and applications a tracking mount will significantly increase output. These mounts track the sun's movement automatically throughout the day.
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