The impact of harmonic distortion on the power quality, caused by solar inverters, is strongly affected by the spectral characteristic of the grid impedance at the point of common coupling (PCC). The grid impedance at a PCC can be modelled as a parallel connection of the equivalent impedances of the grid structure and the solar inverter system. Yet, it is challenging to determine the exact frequency characteristics of these parameters. It requires detailed spectral models, which are often not available especially for the grid. In this contribution, both parameters are measured and evaluated in the frequency range from DC up to 20 kHz. In order to analyse the impact, the impedance is measured on a test grid structure and a PCC. In particular, this paper analyses the influence of the number of parallel-connected inverters as well as the operation point and the integrated mains monitoring system on the resulting spectral grid impedance.