Multiple Tilts – Weight Constrained Roof

TerraGen worked with the project developer and the building structural engineer to identify the structural reserve capacity in order to proceed with confidence.

The Challenge

TerraGen was contacted by a solar developer that was facing a structural challenge on a school PV project that they were looking to install. The issue was that there were many roof sections with varying roof elevations and varying structural reserve capacities. The developer wanted to maximize the PV system capacity, and to achieve their desired kWp, the smaller roof sections had to be utilized. The smaller roof sections had smaller arrays, which had fewer modules able to share in the uplift resistance, meaning a greater amount of ballast was needed.

The increased ballast requirements caused a higher distributed load than the building structural engineer would allow. The building owner suggested that mechanically fastening the PV array to the building structure was not an option.

To utilize the smaller roof sections, a creative design was required, that would allow the developer to maximize the PV capacity by installing solar on these roof sections, while maintaining the array distributed loads within the identified structural limitations.

The Solution

TerraGen worked with the project developer and the building structural engineer to identify the structural reserve capacity on each of the roof sections. Once the limitations were understood, TerraGen was able to reconfigure the layout by utilizing the TGR flat roof system. The flexibility of TerraGen’s TGR flat roof mounting system provided the developer the benefit of being able to change the racking design to accommodate and overcome the building restrictions.

It was determined that the best way forward was to maintain the same module F-F dimension throughout the whole site, but on the roof sections that were structurally challenged, to reduce the tilt angle. By reducing the tilt angle to 5 degrees on the challenged roofs, but maintaining the 10 deg F-F dimension, the distributed load was significantly reduced and within the structural restrictions.

The Result

With no requirement for building structural reinforcement or major changes to the system, the developer was able to proceed with the rooftop PV installation. The project consisted of 756 modules totaling 230.58 kWp. 629 modules were installed at a 10 deg tilt angle, and 127 modules were installed at a 5 deg tilt angle. Another project saved.