For solar contractors looking to expand from residential into commercial solar, flat roof ballasted racking can be intimidating compared to more standard rails and flashings. The purpose of this article is to highlight some of the key factors to consider when designing and planning around flat roof arrays and how that preparation can pay off in high wind loads.
First, assess the wind speed and snow load of the project area against the unobstructed flat roof space. The objective is to prevent uplift from the modules in the event of windy conditions. Aerocompact, a leading ballast racking manufacturer, offers a free online design tool that incorporates historical wind speed, snow load data, and parapet height to generate a precise ballast plan for your local authority having jurisdiction (AHJ). Just like in residential solar, designers must first verify that the roof can accommodate the weight of a solar array.
Select a ballast tilt for your modules. While a higher degree tilt can yield more energy, the tradeoff is that the higher tilt acts like a sail and creates uplift that requires more ballast blocks and weight on the roof. A higher module tilt increases inter-row spacing to mitigate inter-row shading between modules. These factors can play a factor in achieving incentives based on azimuth and fitting enough modules on the roof.
Position the modules on the roof design. The Aerocompact design tool integrates thermal breaks in the arrays, provides a design package for permitting and generates a complete bill of materials.
In September 2017 Hurricane Maria struck Puerto Rico with over 250 km/h winds. The picture below illustrates an Aerocompact array in Puerto Rico surviving intact with no damage. “We were more than happy when we received the pictures showing our east/west system on the flat roof. The hurricane made landfall and hit the territory with winds up to 250 km/h,” explained Irina Schiffner with Aerocompact. It once more demonstrates how important it is to calculate precise static reports for each project to make sure that the racking systems are reliable and can withstand the highest wind loads.