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.
A ballasted system is a flat roof racking system, typically used on flat or low sloping roofs. This racking system is typical in larger commercial projects where the property owner wishes to make minimal penetrations while adding solar to their location. In a ballasted racking system concrete blocks are placed in the system in order to weigh down the solar array and prevent the panels from being affected by weather elements like wind or snow. Next, we will go over 3 key steps a contractor should take when introducing themselves to the world of ballasted racking.
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. Some ballast racking manufacturers offer free online design tools that can incorporate 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 part in achieving incentives based on azimuth and fitting enough modules on the roof.
Find the right design software for your project. Once you have that, position the modules on the roof design. The BlueSol design tool simulates the behavior of the PV system in all its components, provides a module layout overview, and is downloadable via an activation code that you receive. Other valuable design tools include Unirac’s U-builder and IronRidge’s ballast design assistant. Both of which can also design specifically for ballasted racking systems.
In September 2017 Hurricane Maria struck Puerto Rico with over 250 km/h winds. The island's electoral grid was extremely damaged and many were left without power; it’s estimated that 80% of the grid was offline. However, with proper planning, ballasted racking systems were able to withstand the wind. Thanks to ballasted racking, and solar in general, the island sees a new more secure solar energy future. 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.