A method for determining an optimal placement of measurement units for estimating the state of a physical power distribution grid comprising a set of nodes and a set of branches, the method comprising the following steps: I. provide a model of the power distribution grid comprising the topology (nodes), the lines with their resistance and inductance and nominal capacity, as well as the nominal capacity of connected loads and generations at every node; II. specify a hypothetical monitoring infrastructure for the model of the power distribution grid, the hypothetical monitoring infrastructure comprising at least one randomly placed measurement unit, wherein any node of the power distribution grid that is equipped with a measurement unit according to the hypothetical monitoring infrastructure is called hereafter a "measuring node"; III. assess whether the placement of the at least one measurement unit in the monitoring infrastructure is compatible with a two-stage state estimation method, wherein the first stage of the method consists in implementing a Minimum Norm SE for each scenario comprised in a set of stochastic scenarios for loads and generations, the Minimum Norm SE using as input for each particular scenario, measured data corresponding to the particular scenario, since in order for the placement of the at least one measurement unit to be compatible with the two-stage SE method, the result of the first stage must be controllable, and wherein the second stage of the method consists in implementing a Weighted Least Square SE for each scenario in the set of stochastic scenarios, using as input for each particular scenario, the measured data corresponding to the particular scenario and non-zero values estimated in the first stage of the method for the particular scenario, since in order for the placement of the at least one measurement unit to be compatible with the two-stage SE method, the result of the second stage must be observable; IV. if the placement of the at least one measurement unit is compatible with the two-stage state estimation method, determine the means and the standard deviation of the second stage State Estimation error, and record the placement of the at least one measurement unit along with said means and said standard deviation; repeat steps II to IV until at least one hundred measurement-unit placements have been recorded; V. select a measurement-unit placement that comprises a minimum number of measurement units from the recorded measurement-unit placements that satisfy the condition | μ s | < A, with A ∈ R +, and/or the condition | σ s | < B, with B ∈ R +; VI. provide the physical power distribution grid with a monitoring infrastructure comprising measurement units placed according to the measurement-unit placement selected in step V. I. provide a model of the power distribution grid comprising the topology (nodes), the lines with their resistance and inductance and nominal capacity, as well as the nominal capacity of connected loads and generations at every node; II. specify a hypothetical monitoring infrastructure for the model of the power distribution grid, the hypothetical monitoring infrastructure comprising at least one randomly placed measurement unit, wherein any node of the power distribution grid that is equipped with a measurement unit according to the hypothetical monitoring infrastructure is called hereafter a "measuring node"; III. assess whether the placement of the at least one measurement unit in the monitoring infrastructure is compatible with a two-stage state estimation method, wherein the first stage of the method consists in implementing a Minimum Norm SE for each scenario comprised in a set of stochastic scenarios for loads and generations, the Minimum Norm SE using as input for each particular scenario, measured data corresponding to the particular scenario, since in order for the placement of the at least one measurement unit to be compatible with the two-stage SE method, the result of the first stage must be controllable, and wherein the second stage of the method consists in implementing a Weighted Least Square SE for each scenario in the set of stochastic scenarios, using as input for each particular scenario, the measured data corresponding to the particular scenario and non-zero values estimated in the first stage of the method for the particular scenario, since in order for the placement of the at least one measurement unit to be compatible with the two-stage SE method, the result of the second stage must be observable; IV. if the placement of the at least one measurement unit is compatible with the two-stage state estimation method, determine the means and the standard deviation of the second stage State Estimation error, and record the placement of the at least one measurement unit along with said means and said standard deviation; repeat steps II to IV until at least one hundred measurement-unit placements have been recorded; V. select a measurement-unit placement that comprises a minimum number of measurement units from the recorded measurement-unit placements that satisfy the condition | μ s | < A, with A ∈ R +, and/or the condition | σ s | < B, with B ∈ R +; VI. provide the physical power distribution grid with a monitoring infrastructure comprising measurement units placed according to the measurement-unit placement selected in step V.