How to calculate the number of solar racking
June 28 , 2017
Before choosing the solar racking , there are a few other key pieces of data must be gathered, such as:
1: Type of roof surface (asphault shingles, concrete tiles, gravel, etc.)
2: Length and width of the array space
3: Number of rows
4: Thickness of the roofing material between your mount placement and the rafters or other structural members
5: Distance between the beams
As you shop for rails and mounts, beware of the weight of the material and type of metals used. Lightweight aluminum rails and stainless steel hardware is the preferred combination. The aluminum keeps the structure lightweight, while stainless steel fasteners are strong, durable, and do a better job of resisting galvanic corrosion than galvanized steel.
To calculate the exact length of each row, start by retrieving the module's width from its spec sheet. Then multiply that dimension by the number of modules in each row. but you'll have to factor in extra space for fasteners and any other requirements specified by the racking product instructions. For example, the rail installation might call for:
1: an inch between each pair of modules for clamp fastening
2: room for a half-inch clamp at either end of the rail
3: a two inch-margin of extra rail space on each end
The final equation looks like this:
Array Rail Length = ( #Modules X Module Width ) + ( Mid-Clamp Size X
( #Modules - 1 ) ) + (End Clamp Size X 2) + (Margin on End X 2)
For a landscape orientation (sideways), use module length instead of module width.
For our sample 20-module array, the math is thus: (10 X 39.1") + ( 1" X (10-1) ) + (1/2" X 2) + (2" X 2) which equal extra spacing adds up to 405". The next easy calculation determines how many row lengths the rails will have to cover.
Rail Rows = Module Rows X 2
Since two rows of 10 modules will accommodate the 20-module array, the math is 2 X 2, which equals four total array rail lengths. Next you'll have to decide which quantity of the available standard rail sizes will do the job for the least amount of money. This equation is divided into three parts:
Step 1: Of Rails Per Row = (Array Rail Length / Standard Size)
Let's look at the larger size rail of 162" first. When that's divided into the rail length of 405", the result is 2.5 rails. The second size 136" divided into 405" yields a result of 2.97. This number rounds up to 3. Now on first glance, you might conclude that 2.97 rails isn't be long enough to create one array rail length out of three 136" rails. However, the opposite is true, and three rails will exceed 405" by three inches. (Here's the math: 3 X 136"= 408".)
At this point, both sizes appear to fill the order efficiently, leaving little or no waste material. Let's move on...
Step 2: Of Standard Size Rails to Order = ROUNDUP ( #Rail Rows / #of Rails Per Row )
The math for the 162" rail looks like this: 4 X 2.5 = 10 rails. "Round Up" means a decimal number must be raised to the next highest whole number or integer. Since 10 is a already a whole number, it doesn't need to be rounded up. Meanwhile, the math for the 136" size is this: 4 X 2.97 = 11.88. Since 11.88 isn't a whole number, we must round it up to the next integer, 12.
So now we know that we can order either 10 rails sized 162" or 12 rails at 136" for our array. Before checking their prices, we must also factor in the number of splice kits we'll have to order in conjunction with each standard size of rail under consideration. Thus:
Step 3: Splice Kits = Rail Rows X ROUNDUP (of Rails Per Row)
For the 162" rail, the math is thus: 4 X (RoundUp 2.5) = 4 X 3 = 12. For the 136" rail, the solution is 4 X (RoundUp 2.97) = 4 X 3 = 12. The number of splice kits is the same for both option. Consequently, this will have no impact on either the price or the labor time spent installing them.
Pricing is the next step in our journey to choose a rail size. Keep in mind that rails are long lengths of non-foldable metal requiring shipment in a truck. If you or your installer are not picking up the material from the supplier, there may be an additional charge for the longer rail, since 162" translates to 13.5 feet, while 136" is a somewhat less wieldy 11.3 feet. With all these details in mind, here's the the final calculation concerning the rails and splices.
Step 4: Cost for Rails = (#of Standard Size Rails to Order X Price per Rail )
+ (#Splice Kits X Cost per Splice Kit) + freight charge
When the time comes, you can perform this math on your own to see which standard rail size is most cost-effective. Next, you'll have to consult the product literature to determine all the fastening hardware and quantities required to get the job done (plus a few extras of each part). Most of the time, you'll use the same products regardless of the rail size you choose. Here's a list of common parts and the mimimum number of them required:
1：Mid clamps - installed between two modules to hold them against the rails. A standard calculation for the order quantity is:
#Mid Clamps = #Modules - #Module Rows
2: End clamps - one installed at the end of each rail on the outer module. A standard calculation for the order quantity is:
#End Clamps = #Module Rows X 4 or #End Clamps = #Rail Rows X 2
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