Solar Racking Made Simple: What You Need to Know About Designing Your Solar Energy System
Installing a solar energy system can be a challenging task. A home solar panel installation will include up to or more than a thousand parts so gathering the right component parts can take a lot of time researching what each part is and what each part does. One critical component of your solar energy system is the solar racking, otherwise known as solar panel mounts. The solar rack is the hardware under the solar module that secures the panel to a surface (roof, ground, pole) in the panel installation. If you don't get this right, then forget it-you are just buying yourself years of trouble. In this learning article, we will focus on how to select the proper solar racking.
Space Available for the Solar Energy System
The first step in evaluating which solar rack to use, you must first evaluate the space available for the home solar panels. Either on the roof, on the ground or on a pole, you need to know the square footage before you begin the selection process. Measure the length and width of the surface on which you intend to place the solar panels. And if you are installing the solar energy system on the roof of your home, remember you are only measuring that portion of the roof with a southern exposure (and not shaded by a 70 year old oak tree). You will have to subtract that portion of the roof on which there are any obstructions such as chimneys, skylights and vents. Consult with local and state building, electrical and zoning codes to make sure that you can comply with applicable laws and ordinances. Once you have the measurements, draw a diagram so that you can reference it later.
Dimensions of the Solar Module
Next we will need to evaluate the length and width of the solar module you will be using. Each home solar panel has its own specific measurement so consult the panel's specification sheet for the solar modules you are considering. Once you have the dimensions, write the information on a sheet of paper so that you can determine the rail length you will need for installation.
For our example, we will use one of the leading solar modules that we sell at SolarTown, which has a width of 39.4 inches and a length of 65 inches. For the width, we will round up to 40 inches per module. We are assuming for this installation that the panels will be installed side-by-side in a portrait orientation. As most installers recommend leaving a small space between panels, we will round up the length of the panels to 66 inches.
Number of Solar Modules
The next step then is to calculate the total number of solar modules we want to mount at our site. Remember that there are different solar mounts used for each application: flush mounting for roofs, solar pole mounts, and solar ground mounts.
In our example, let's say that we want to get the most number of panels on our home. If the total length of our surface is 30ft (360 inches) left-to-right and 20ft (240 inches) top-to-bottom, we need to confirm how much unobstructed space is available for the panels we want to install. And you do not want to install the solar array right up to the edge of the roof. For our example, we will assume that the panels are installed up to 12 inches from the edge, as may be required by local building codes, and that there are no obstructions on the roof.
The next thing is to divide the top-to-bottom length of the roof by the long edge of the panels to come up with how many rows will fit in the space available. We are assuming that the panels are going up in a portrait orientation. Divide 216 inches, which is the top-to-bottom length of the roof minus the 12 inch border on each side, by the long-edge of each panel and you get 3.3 panels -obviously you cannot cut a panel so you can get three rows on your roof.
Do the same calculation for the number of panels across the width of the roof (336 inches ÷ 40 inch panels = 8 panels or 8 columns across the horizontal width of the roof. Altogether, you can get 3 rows and 8 columns or 24 panels on the roof in a portrait layout with 12" of room on each side of the array.
Solar Rail Selection
At this point of the installation, you are now ready to pick the rails. You have already figured out where the roof supports are and that your roof can hold the added weight of the panels. The standard spacing for roofing rafters is 16 inches and standoffs, which are posts bolted to the roof rafters, are spaced up to 48 inches. If the structure of your roof is non-standard, you may want to talk with an engineer.
To pick the right rail, we need to know the combined width of the panels in a portrait configuration. We are going to simplify this example. Let's assume that that you want to install four panels across in a portrait configuration. The combined width of these panels, using the dimensions that we gave earlier, is four times 40 inches, or 160 inches. We will need a rail long enough to cover the 160 inches and remember that each module needs to be attached to two rails.
For rails, it is always better to have a longer rail compared to a shorter rail so in this application anything equal to or greater than 160 inches will be fine. You want to make sure that the rails extend beyond the measurement of the panels. You can cut the rails to size after you have installed the rails. You can peruse the lengths of the rails that SolarTown has available in the solar racking section of the store. One of the leading manufacturers, Unirac, manufactures a UniRac Rail 168 inch standard rail. There will be eight inches of extra railing, which we can cut for a perfect fitting.
Choosing the Clamps
Once you've determined how many panels your site can handle, and the rails necessary to hold the panels, the last step is choosing the clamps that secure the modules to the frame. Most modules are between 1.00" - 2.00" thick. Clamps come in varying sizes and the devil is in the details! Review the mechanical dimensions on your module spec sheet and note the thickness of the panel. Then select an end-clamp and mid clamp or a cap strip to hold the panels down.
End clamps install on the outer edges of the array, and mid clamps install between columns of panels. A cap strip is an alternative that functions as a clamp, but gives a sleeker look for the array as a unit. Cap strips come in lengths to match the rails you've chosen. Top-mount clamps are the most common attachment method, and support modules between .9" and just over 2.0". Know the thickness of your modules and pick the corresponding end clamps, mid clamps or cap strips for the finishing part of the install. SolarTown offers all the necessary clamps or cap strips to support your installation.
The installation of your solar energy system for your home is going to take 1 or 2 days and you will enjoy solar energy for 25 years or more. But you need to put in the time to design your system, and the solar racking is a critical component of your system.