Power quality (PQ) becomes a more and more pressing issue for the operation stability of power systems with renewable energy sources. An important aspect of PQ monitoring of distribution networks is to compare the PQ indicators in different operating conditions. This paper evaluates the impact of a microgrid implementation in a real distribution network on power quality indicators at the point of common coupling in an LV network. The study includes a classical assessment of the long-term PQ parameters according to the EN 50160 standard, such as nominal frequency deviations, voltage RMS variations, voltage fluctuations (represented by long-term flicker severity), voltage unbalance and total harmonic distortion. The PQ evaluation is extended in statistical assessment based on cluster analysis. The case study contains 5 weeks of power quality observation results obtained at the assessment point in two different working conditions of the distribution system: before and after implementing the microgrid. The study allows establishing general conclusions regarding a microgrid interconnection in order not to exceed power quality limits and considering the influence of photovoltaic generation on power quality parameters.