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Photovoltaics

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 45 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 15 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.

Photovoltaics

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