The ever-increasing penetration of power-electronic-based renewables is challenging the power quality and stability of electric power grids. Classical low-order harmonic profiles are expected to change while high-order harmonic distortions are being aggravated by the fast switching operations of electronic power converters. The wide timescale control dynamics tend to cause interactions among converters in renewable energy systems, such as wind/photovoltaic power plants, distribution/micro-grids, and further with the power supply network. There is consequently a great interest in the academia and industry on the need of properly modeling grid-connected power converters for harmonic studies. Both wind and photovoltaic systems will be addressed at all voltage levels (low, medium and high voltage). The panelists will present theoretical aspects and practical case studies.