Top Six Reasons to do a Ground Mount vs. Roof Mount

Ben Farmer's Ground Mounted Solar Array

Most of the PV installs people see in their community happen to be placed on top of a home’s roof. While this is aesthetically pleasing, space saving on the property and out of the way from people’s hands there are a few drawbacks to this method, which I have outlined below.

1. If the angle and orientation of the roof is not ideal then you will lose some percentage of your overall production. Ground mounting allows you to be more flexible in both regards.

2. Maintenance on your PV array may be required in the future and having to trouble shoot an array on the roof is much more time intensive and dangerous than a ground mount array which allows you you to walk right up to the array and easily navigate around it for maintenance and trouble shooting.

3. Performance with a ground mount system will always be better than roof top arrays since the system on the ground has more airflow to cool down the panels vs. having the array on the roof and within inches of a hot surface.

4. Your PV system is designed to run for many decades to come and the odds are your roof will need to be replaced before the end of the PV systems lifetime. Ground mounting will make sure you will not have to take down and reassemble your array when a new roof is needed.

5. For roof top installs the racking system has to penetrate the roof with lag bolts and as any roofer knows the more hole penetrations you have the more chances for failure in the future. Installing your PV array with a ground mount will guarantee not to interfere with your existing structure and will also allow you the space to mount the panels anyway you like vs. having to conform around roof vents, antennas, and other misc obstructions.

6. Room for expansion is usually not as much of an issue with a ground mounted array.

I do see the reasoning to put PV on roofs in locations that do not have adequate space or a good solar window on the ground within the property boundaries. Also, some properties have other problems such as tall trees or a heavily wooded property in general.  I guess one could also say wiring runs are shorter for roof top than ground mounted arrays, but with high voltage grid tie inverters the wire size can be smaller even for longer distances. And for battery based systems there are now high voltage charge controller options such as the Midnight Classic’s or the new Xantrex XW MPPT 80A Solar Charge Controller (up to 600V DC input!) to keep wire size down. I’m sure others could come up with a host of “custom” situations where roof would be better. But that’s just it, most all installs are custom, but I’d say in general, a ground mounted array is the best choice if you have the option to do so.

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Ben Farmer

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5 Comments

  1. tom m

    Don’t forget to add ease of maintenence for cleaning and lower installation costs….

  2. Thomas Taylor

    This is really good info.
    But as I live in the city and theft is high.
    Roof mount is my only choice.

  3. Matt Boschen

    A few of these categories apply to specific areas more than others.

    As an installer heading into my 4th year and having done installs all over the country, I have found that in my area (New England), it’s a real challenge to install a ground mount for two reasons. One is simply because of the trees! Wherever there is space in a yard, is typically much lower than the house and tends to get a lot more shade than a roof. One such instance at a customer’s house, the roof received 4.21 sun hrs per day according to our pathfinder report. The location for a ground mount near the tree line (was their hopes) ended up only getting 3.12 sun hrs per day, a 25% reduction! If your customer has the space (and clear skyline) from way down on the ground, then they can be worth it. I have found this is usually the case in larger wide open places where there’s not a lot of trees- more like New Mexico or Utah. That being said, I have installed several ground mounts and dozens of pole mounts throughout New Hampshire- they do work, but you need clear space in front (south) of an either side of (E-W) your installation site. The 2nd reason I have found it so hard to do ground or pole mounts in New England is the amount of ledge we have here. Almost every ground or pole mount here has resulted in needing to drill and pin a pole to the ledge or the use of dynamite to blast the ledge out- both up the bill dramatically- often making the entire installation prohibitively expensive.

    As far as roofs wearing out before installations- If the roof isn’t new (within the past 5 years), we always recommend getting a new roof first. Often I’ll work with customers and talk them into a standing seem metal roof if possible. This really is the way to go- as they last much longer than an asphalt roof, and you need ZERO roof penetrations! With standing seems, the solar mounting clamps crimp onto the seems of the roof- no penetrations for lag bolts. The only penetrations you need are for the wires, and even those typically run up under the cap without changing the integrity of the roof- ZERO penetrations! I have done several roof mounts at municipal buildings, schools, and businesses this way. The metal roof is also good for your customers interested in a rain-water-catchment system, if they want to get off city water, or have a contaminated well, or are worried about future well contamination. A Metal roof if probably 4/5 of the equation- catchwater cisterns are the rest, but once the roof is in, everything else is set up, all the ducks are in a row. … I’ll leave a conversation about why we should all have metal roofs for another topic!

  4. Rahul

    Thanks there guys.. Good Info. I was planning to use Roof Mount. But now i need to double check!!

  5. Calvin Walker

    Hi Everyone, I have created a Tool Set for finding underlying rafter centers on shingle/composition roofs. Inside the attic a rafter clip holds and references a tape measure to the first rafter of a horizontal run. The tape is pulled across perpendicular to rafters to the end rafter of the horizontal run and attached to the end clip. Rafter centers are then marked onto the tape, the tape reference is “Translated” to the outside of the roof, translation plates hold and reference the tape measure along the horizontal run on the outside of the roof where the marked rafter centers can now easily be transferred to the roof. http://www.trucenterrafterclips.com I believe this Tool Set will be a great advantage to the one time or first time installer who may not be comfortable with the “sounding”, method or drilling “test holes” in there roof.

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