As an Amazon Associate, this site earns commissions from qualifying purchases. For more details, click here.
Installing solar panels on rooftops can be challenging. There must be enough space on your roof but you have to make sure there is ample room between each panel too. But how much space is required, and why is it necessary in the first place?
Solar panels must have at least 4 to 7 inches of space between rows because the frame contracts and expands as the weather changes. There must also be at least 12 inches of space between the solar panel and the edge of the roof to comply with building codes and to keep the array secure.
Why is There a Gap Between Solar Panels?
The solar panel frame and glass are affected by temperature, contracting and expanding all the time. If there is no space the panels will press into each other and could cause damage. Your solar panel warranty will be voided if there is no space between the panels, so make sure there is a gap.
It is tempting to place the solar panels right next to each other to fit as many as possible, but that is not advisable. Solar panels are designed to work under specific circumstances. A solar array can only be a particular distance from a house before performance is affected, and it holds true for module spacing as well.
The panel frame and the glass covering the cell are durable, but they are not designed to bump into each other. Depending on the weather the modules will get quite hot as well, so you want to make sure there is sufficient gap between them.
Space between Solar Panel Rails and Support
Solar panel rails should have 12 to 16 inches of space between the first support and the end of the rail. Too much space between the rails and the panels could bounce, dangerous during a heavy storm or strong wind gusts. Two rail pieces must also have a rail splice for stability and support.
Space for roof rafters is 16 inches on the average roof, while the standoffs have a 48 inch space between each post. If you are going to install four PV modules measuring 65 x 39 inches each, the combined dimensions will be 160 inches.
Each panel has to be fastened to two rails, and the rail has to be long enough for all the panels. In other words the rail must be at least 160 inches long. If the rail is too long you can cut if off anyway, and it is easier to deal with than being stuck with s short rail.
Solar panel brackets have to be bolted with correct flashing. This will keep the rail from moving and exerting pressure on the other parts. The clamps must also be the right size and number to ensure a proper fit. Remember, your panels are resting on these mounts, so they have to be as sturdy as possible. We strongly recommend the Relmon Z brackets as they are sturdy and well built.
Solar Clamp Size Guide
Most solar panels are 1 to 2 inches thick. Top mount clamps are ideal because they can handle panel thicknesses ranging from 0.9 to over 2 inches. The clamps will secure the panels so make sure that is the right specs for your system.
If you buy a solar panel kit it should include all the clamps required to assemble the system. But if you are installing the panel piece by piece, check your solar panel instructions for the recommended clamp size. This is a critical part of the installation so you have to use the right size. A good choice would be the UI AI Solar Panel Clamp Set which should be fine for most setups.
How Many Solar Panels Can Fit on My Roof?
Assuming you allocate the required space between panels, how many can fit on your roof? For that we have to do some calculating and math.
The distance depends on several factors including the panels’ expansion tolerance, clamp size, bracket type, roof and solar panel size. How the panels are being installed and where also determine the space between rows. You also have to measure only the area where the panels will be installed, so parts shaded by trees cannot be included.
Most solar panels are 5.5 ft x 3.25 ft and occupy 17 sq ft. Rounding the figure to 20 sq ft, you need 60 to 70 sq ft for every kilowatt, space between panels included. For an 8 kw array you need about 500 sq ft.
The average roof size in US homes is 1600 square feet, which can fit 80 solar panels. This assumes no chimneys, pipes or other structures on the roof. This also assumes no part of the roof is shaded. In real world situations that is unlikely so we have to use a different calculation.
If we compute the average roof size with the average area available for solar, it is about 26%. So for a 1600 square foot roof with 25%-30% available space you can install 20 to 30 panels. This is a general estimate only as it will depend on the solar panel size and wattage.
If you require 1000 kwh per month, you would need 35 to 40 250W solar panels. If you buy 375W modules though you would require only 25 to 30.
Most solar panels for homes are 250W to 375W. A good rule of thumb is 1 kw for every 3.5 panels for a 285W module. If you install 340W-375W panels you would require only three. However it does not mean you will save space with a large panel. Whether you go for large or small modules the footprint will be just about even in the end.
Your solar panel installer will determine what solar panel size is best suited for your roof. They will conduct an assessment on the available space to determine which setup provides the best results. They will also assess what solar array configuration is most suited for the energy production you need. if you have a 10kw solar system for instance, there must be enough space available.
The biggest factor is how many kilowatts you want the system to produce each month and how much rooftop space is available. Again, roof space calculations should only account for the usable area, not those near a chimney or skylight.
How Many Panel Rows Can Fit on My Roof ?
For solar panels that will be installed in portrait mode (which is the standard), divide the length of the array by the panel width in inches. To find the panels for each row, divide the array width by the panel length.
Array Length / Panel Width = Number of panels per row
Array Width / Panel Length = Number of solar panel rows
Assuming each solar panel measures 5 1/2 x 3 1/2 feet and available roof space is 14 ft W x 38 ft L, two rows can be installed. This assumes the modules are installed portrait style and at the same angle as the roof. If the panels are 3 1/2 ft wide, ten panels can be installed.
These formulas give you a general idea of how many panels can be installed. But the figures have to be adjusted to account for the hardware specs. This is why there needs to be a few inches of space at the end of each rail. The calculations account for longer rails because it can be sawed off anytime.
How to Calculate Solar Panel Space For Roof – Example
Each solar panel row should have half an inch space between them. There should be 2 to 3 feet of empty space per 2 to 3 rows so a repairman can troubleshoot the solar panel . This is a general guideline as some racking mounts may need more space. Check the racking mount instructions for the specific number.
Here is an example with the solar panels to be installed in portrait. Each panel is 65 inches long and 39.4 inches wide. For convenience the width will be rounded to 40 inches.
The roof space is 360 inches (30 feet) in length and 240 inches (20 feet) from bottom to top. To calculate how much space can be used for solar panels, you have to subtract 12 inches from the edge on each side 924 inches total), as that is the limit in most US building codes.
Subtract 24 inches from the roof top to bottom surface:
240 – 24 = 216 inches
Divide 216 inches by the solar module length:
216 / 65 = 3.3
You can put 3 solar panel rows on the roof.
/subtract 24 inches from the roof width surface:
360 – 24 = 336
Divide 336 by the solar module width:
336 / 40 = 8
You can install 8 columns on the roof. 24 solar panels arranged in 3 rows and 8 columns can be installed on a 30 ft x 20 ft roof with 12 inches of space available on either side.
As you can see a lot of factors are considered when installing solar panels. The 4 to 7 inch gap is recommended, though you can make it larger. The challenge is to balance the spacing with maximizing the available rooftop space, which is why planning is very important.