The wind loading of ballasted solar systems on roofs is not covered by EN 1991-1-4, i.e. the part of the Eurocode that defines wind loads on buildings and structures. Some national standardization bodies have issued National Annexes to fill this gap. National Annexes, such as ÖNORM B 1991-1-4, or the purely informative Dutch standard NEN 7250, include pressure coefficients for mounting systems that are more or less applicable to aerodynamic PV flat roof systems, but they do not provide an economic design.
In 2019 and 2020, a technical committee, together with the leading wind tunnel experts in the DACH region, worked on a guideline for the design of mounting systems for PV modules based on wind tunnel tests in boundary layer wind tunnels. Central topics were:
The ultimate limit state or its interpretation for substructures based on the EQU concept according to EN 1990, equations for positional safety (derived from the governing load cases), load influence areas and a methodology for testing the load-distributing effect of the system composite, parameters of the building (such as length, width, height, parapet height), roof fixtures and basic building shape which affect the wind load, as well as the effects of the terrain (around the project site) on the peak velocity pressure. In addition, the application of a factor KFI = 0.9 for damage consequence class CC1 to roof-mounted rack systems for PV modules was found to be non-compliant with EN 1990.
The committee work was coordinated by the German Solar Industry Association (BSW). Dr. Thorsten Kray, Head of Research & Standardization at AEROCOMPACT provided valuable input on the required contents of the reference paper with his expertise on wind tunnel tests collected over a period of two decades at various research institutions. The key topics addressed by Dr. Kray were: the inflow in the boundary layer wind tunnel, the design and scale of the wind tunnel model adapted to the scale of the flow simulation, the analysis of the pressure coefficients, the experimental determination of the system composite, the determination of the required attitude ballast and the state-of-the-art documentation in the test report.
AEROCOMPACT's involvement in the key topics of the reference paper is documented in several info-figures. Figures 2 and 3 show the two methods suitable for the experimental determination of the system composite, while Figure 4 shows the S10 system installed on the roof of the AEROCOMPACT headquarters in Satteins, Austria. The figure above again shows a flow visualization over the Aero Z+ east-west system.
In 2021, the guidance paper was published. The provisions contained are consistently applied in the AEROTOOL to ensure the efficient and safe design of our substructures for solar modules.