The interaction between flat weak rooftops and the Rable system

Abstract

Due to the increasing demand for energy and the growing desire to reduce the dependence on fossil fuels in response to climate change, there is significant demand for rooftop solar panel installations. Unfortunately, a large part of roofs currently cannot support solar panels due to structural limitations. These roofs are typically designed to withstand only the weight of their own construction, for example isolation material, and the roof covering, and the snow loads imposed by the NEN-standards, and not the heavy weight of conventional solar panel systems or other installations. Rable has developed a construction solution specifically designed for roofs that would otherwise be too weak for solar panel installations.
The Rable system is a rigid structure composed of centers and sides that together form trusses in two directions. As a truss system, it is significantly stiffer than a standard solar panel structure. This increased stiffness allows the installation to transfer a portion of its weight to the purlins, which, in most cases, can handle more load than just snow. In addition, the Rable system is lighter than standard solar panel constructions.
To determine the actual deflection of the Rable system and understand how much it relies on the roof structure, the centers and sides were first analyzed separately under the load of the Rable system. The resulting deflections were then combined to calculate the deflections for various setups. Once the deflection of the Rable construction without a supporting roof was determined, additional calculations were performed for different configurations to evaluate how much the combined roof and the Rable construction would deflect, how much weight would be transferred to the purlins, and how much insulation would compress at the contact points.
To ensure that the construction is strong enough to support itself, the stiffness added by the Rable system to the roof was analyzed. In all but one setup, the construction added sufficient stiffness to support the additional weight. This means that the Rable system can be installed on most roofs.
To verify the deflection calculations, a 3D model was developed and the deflections were analyzed using the Finite Element Method (FEM). Although the FEM results aligned with the calculations in many cases, discrepancies were observed for some setups. These discrepancies were attributed to the fact that the FEM model was not extensive enough to include elements outside the observed section, which are necessary to counterbalance the system. This resulted in the Rable systems deflecting more in the FEM model for certain setups. However, for other setups, the FEM results matched the calculated values from the study.

In conclusion, the Rable system offers a viable solution for installing solar panels on structurally limited roofs. Its lightweight and stiff design, combined with its ability to transfer a significant portion of the load to the purlins, makes it suitable for many applications, provided that the specific roof conditions and materials are thoroughly analyzed and that an good solutions or alternative has been found for the current cable.