Solar Mounting – Ground or Roof?

Mounting Options for Solar Arrays:

Ok folks, there are two options for mounting solar panels. One is roof mount, the other is ground mount. We are going to discuss the pros and cons of each and Ill sprinkle my opinion in along the way.
Rooftop solar arrays are restricted by the characteristics of the roof on which they are installed. If your roof is at a bad angle, doesn’t face south, or has obstructions like chimneys or skylights, then your solar array will be less productive. On the other hand, ground-mounted solar panels can be located wherever the conditions are best.

Generally, ground mount solar panels cost a bit more than rooftop solar on a per-watt basis because of additional labor and permitting that may be required for the installation. That being said, if your property isn’t ideal for rooftop solar, installing a ground-mounted system can actually save you more money in the long run.
In addition, if your home uses a lot of electricity, your roof might not be big enough for a solar energy system that meets your electricity needs. In contrast, ground-mounted solar systems can be sized to match your electricity consumption without the space restrictions of a rooftop system.
One of the reasons we tell people to perform an energy audit, and put together a usage reduction plan first, is that if you dont, you are going to run out of real estate(roof or ground) before you meet your needs. If you need 1200 sq ft of roof dedicated to solar, but only 800 sq ft of your roof faces south, you can see what I mean. Now that being said if you are going to be going with a roof mounted system, and you have already maxed out your conservation, then going with more efficient, but also more cost per watt panels may be the right option for you.
When you mount on your roof, your panels are going to be hader to access to maintain, and we know clean panels are always the goal. Not cleaning pollen, dust, and other buildup from panels can have a big impact on your output. Snow buildup is another consideration that must be taken into account for a roof system. you cant easily get onto the roof to clear snow after a storm when your panels are on the roof. Additionally, in the summer your panels will be hotter because there is less airflow behind them up on your roof. Hotter panels are less effective.
When mounting solar panels on your roof, you take advantage of a space that is otherwise not being used. You are not sacrificing precious rreal estate on the ground, and while im not aware of any studies, I would imagine that the little bit of shade on the roof itself may have a degree or two impact on your attic temps which might reduce your overall cooling load in the summer. You dont have to dig a trench to bury transmission lines with a roof mount, and there is no excavation or heavy equipment needed for a roof mount system.
Now lets talk a bit more about ground mount systems. Obviously when putting in a ground mount system, you can place the panels at the exact tilt and azimuth you choose, which is best for your goals. Due south might not be the best option in your are due to shading considerations.
The ideal is to have a shade-free array throughout the entire day, from dawn until dusk. However, obstructions such as trees, buildings, and mountains are common. Early morning and late afternoon sunlight isn’t as powerful as those midday hours, so aiming for a shade-free “solar” window from 9 a.m. to 3 p.m. will give you most of the energy available at the site assuming that you dont have any shading issues. If you have great sun from 10 to 5, like we do at our homestead, you might cange your azimuth a little bit to take advantage of that. Ground mount also allo for multiple azimuths, so you might have most of your panels facing one direction, but have a few panels off by a few dozen degrees to take advantage of afternoon or morning sun, as your conditions may require.
Now when working on a ground mount system, many people utilize tracker systems.
The angle at which the sun’s rays meet the surface of the solar panel (known as the “angle of incidence”) determines how well the panel can convert the incoming light into electricity. The narrower the angle of incidence, the more energy a photovoltaic panel can produce. Solar trackers help to minimize this angle by working to orient panels so that light strikes them perpendicular to their surface.
There are two types of solar tracking systems: single-axis and dual-axis.
A single-axis tracker moves your panels on one axis of movement, usually aligned with north and south. These setups allow your panels to arc from east to west and track the sun as it rises and sets. Imagine as the sun traverses the sky, the panels move along with it, then reset themselves in the evening back to east.
A dual-axis tracker allows your panels to move on two axes, aligned both north-south and an east-west. These systems maximize your solar energy collection throughout the year. It can track seasonal variations in the height of the sun in addition to normal daily motion.
If you are on an off grid, homemade mount system like we are, you can also utilize a single tilt system that only adjusts the angle based on the time of the year you are in and guided by the height of the sun in the sky. When we put our system in, I couldnt find a reasonable price for a single axis traker so we just built our own mounts and adjust them a little bit here and there over the course of the year.
The closer to the equator you are, the less effective a dual tracking system is because there is less variation in the winter and summer sun. Where I do consulting work, typically south of the Ohio River, I advise my customers to evaluate a single axis and not to even look into dual axis. Panels are so cheap that you can add panels for less expense than adding a second axis of tracking.
In summary, if you have the real estate and relatively soft ground, a single axis pole mount single axis tracker is the way to go.  A standard, non tracking ground mount system would be next best, unless your roof just happens to be at a great angle and azimuth and of the proper size for your solar needs, in which case its a toss up.
 

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