The subject matter of the invention is a method of measuring a grounding current of a photovoltaic power system incorporating a photovoltaic inverter, a measurement current being led through two shunts (Rs1, Rs2) disposed at different points, the measurement current being a current that may flow alternatively at two different points at different electric potentials, the current flowing at a potential that differs by at least 50 V from the potential of the point of evaluation, the shunts (Rs1, Rs2) being inserted in such a manner in a current mirror circuit that the voltage drop caused by the measurement in the shunts generates an asymmetry in the current mirror the magnitude of which is proportional to the measurement current, and the measurement current being the grounding current of the photovoltaic power system with optional positive or negative pole grounding.