Photovoltaic (PV)-modules are not only exposed to static mechanical loads, such as snow and wind loads (for building integrated modules), as tested in the current standard IEC 61215. The highly dynamic loads occur when wind triggers oscillations. It is obvious that the dynamic loads are more likely to cause fatigue of materials, especially of PV-cells and connecting wires. The dynamic behavior of modules with different designs and sizes is analyzed by different methods. Outdoor measurements of the deflection show the dynamic behavior of different types of modules under wind loads and the correlation between wind speed and deflection. Numerical calculations, based on FEM-modeling, showed that their resonance frequencies are typically in the range from 1Hz to 100Hz, depending on the modes. Results of the outdoor measurement and numerical simulations are reported.