Understanding Height and Clearance: Critical Design Parameters for Utility-Scale Solar Racking

Understanding the intricacies of utility-scale solar racking design is crucial for successful project implementation. One of the most fundamental aspects is the careful consideration of minimum clearance and maximum height parameters. These specifications play a vital role in both fixed-tilt and tracker systems, affecting everything from snow management and vegetation control to wind loading and local zoning compliance.

In this except from HeatSpring’s comprehensive Utility-Scale Solar Design Applications course, instructor John Selby breaks down these critical parameters and demonstrates how designers can account for them in their system designs.

For professionals looking to master utility-scale solar design principles, the Utility-Scale Solar Engineering bundle offers in-depth training that includes actionable PVcase tutorials alongside essential design considerations every utility-scale solar professional should know.

Transcript below.

Let’s examine another key term in the design parameters for the racking and that is minimum clearance and maximum height. You can see here what those parameters look like for each of our two main racking types. 

With fixed tilt, it’s a pretty easy concept to grasp, since everything stays put.  

For tracker systems; however, you have a moving part which both decreases the clearance and increases the system height as it moves throughout its daily cycle. So now you’ll need to factor in the height of the system at its maximum rotation or height.  

One key way that ground clearance and maximum height are varied or adjusted is by changing what’s called post reveal. Reveal is the distance from the ground to the top of the post and it’s a key consideration for racking design. 

Let’s start with clearance. 

Typically, the minimum clearance will be determined by the project owner, if they have a technical specification. Then, designers also need to look at maximum snow depths and vegetation control plans to determine how much clearance the racking needs to maintain above grade at maximum tilt. Note: I have a tracker system shown here, but these factors apply for fixed tilt as well.  

When looking at a maximum height, there’s also the wind loading to consider. As modules are tilted higher and higher or are further off the ground, they’re exposed to higher wind loading, and this may either cause foundations to be deeper or heavier steel or may just simply exceed the mechanical rating of the modules or racking. This is really a limitation that will be calculated by the racking vendor, but just something to be aware of, especially in areas with high wind speeds.  

To determine the required clearance and maximum height of a tracker system, you’ll need to know the tracker rotation angle. Tracker rotation angles vary by manufacturer and are typically listed on the datasheets. For the most part, these will be between 45-60 degrees with some manufacturers offering special options for higher angles; for instance, to stow at 75 degrees angle to avoid perpendicular impacts of hail, which is pretty cool.  

Remember that zoning regulations usually restrict the maximum height of a PV array based on the height of the system at maximum tilt. Zoning boards are fairly attuned to system height and may want a graphic like the one a few slides ago that shows the maximum height of the tracker system at full tilt.