Numerical simulation of wind loads on PV systems placed on the ground and a flat roof

Wind loads are a major design constraint for photovoltaic (PV) systems, in particular when modules are installed on flat roofs not connected to the building. Such PV system designs must be heavy enough to assure safe and durable operation under varying and peak wind conditions, but should not be much heavier. The additional weight required for a selected configuration cannot be easily deduced from wind engineering standards (codes) without a calibrated aerodynamic model and without knowledge of the local wind environment. Consequently, risk and lifetime analysis, by means of critical loads for PV panel disposition and fracture initiation due to extreme wind events, as well as fracture worsening due to unsteady aerodynamic loads, cannot be addressed.

To overcome the mentioned limitations, case-specific loading rules have to be developed based on design-specific aerodynamics and site-specific wind conditions within the atmospheric surface layer (ASL), potentially in an urban environment. Numerical simulations provide means to develop such case-specific loading rules. For this purpose, the simulations need to offer sufficient fidelity to enable the prediction of lift and drag forces that act on the selected PV system, simulataneously providing further insight into the flow. Nevertheless, the computational approach is limited by numerical approximations and modeling assumptions. The corresponding numerical and modeling errors manifest themselves by a dependence of the simulated wind loads on the mesh, timestep, selected turbulence model, and inflow condition, among others.

In the contribution, large-eddy simulations (LES) of wind loads on PV systems placed on the ground and a flat roof will be presented. First, starting from the case of a single (South-oriented) PV panel placed on the ground, LES results obtained with OpenFOAM and PVade are compared to each other in order to establish a minimal reference set-up. Second, the geometry is extended to a double-panel (East-West) configuration, which is likewise simulated with both solvers. Third, a single building is introduced in the OpenFOAM-based set-up so that LES for a building without and with a roof-placed PV system are conducted. For comparison, the same PV array is simulated placed on the ground. These results demonstrate the significant influence of the local wind environment on panel-based wind loads and the derived case-specific loading rules. Last, an outlook is given to fluid-structure interaction and fracture initiation.