A method for determining the elements of a photovoltaic solar inverter with an AC grid filter, wherein the inverter (8',8",8′′′) is connectable to the AC grid at a connection point; the inverter (8',8",8′′′) comprises: • at least one power module for converting a DC input voltage into a three-phase AC output voltage; • a three-phase AC/AC transformer (10', 10", 10′′′) for adapting the three-phase AC output voltage of the power module to the three-phase AC voltage of the AC grid, wherein the AC grid has, at the connection point, an inductance "L 2 "; wherein the three-phase AC/AC transformer (10', 10", 10′′′) comprises: ∘ at least one winding on the low voltage side connected to the power module; ∘ at least one winding on the grid side, which is a medium voltage side, connectable in series with the AC grid; wherein the winding on the low voltage side connected to the power module together with the winding on the grid side have an equivalent inductance "L 1 " and an equivalent impedance "X CC "; • a capacitor "C", connected to the winding of the grid side of the three-phase AC/AC transformer (10', 10", 10′′′); wherein the equivalent inductance "L 1 " (L1, 10a, 10b) of the AC/AC transformer, the capacitor "C" (C, 11) and the inductance "L 2 " (L2, 6a) of the AC grid form a high frequency "LCL" filter according to the following steps of the method, which comprises: • defining at least two different values of a Short Circuit Ratio "SCR" at the connection point; • obtaining corresponding values of the inductance "L 2 " of the AC grid at the connection point for each value of the Short Circuit Ratio "SCR" by means of the following formula: L 2 = V n 2 2 πf n ⋅ SCR ⋅ S n • calculating the equivalent inductance "L 1 " of the AC/AC transformer by means of the following formula: L 1 = X cc ⋅ V n 2 2 πf n ⋅ S n • setting a value for the resonant frequency f res of the L 1 CL 2 filter and calculating, for each value of the Short Circuit Ratio "SCR", a corresponding value of the capacitor "C" by means of the following formula: C = L 1 + L 2 L 1 ⋅ L 2 ⋅ 2 πf res 2 • selecting a value of the capacitor "C" between the minimum and maximum obtained values for the capacitor "C"; wherein: X CC: is the equivalent impedance of the windings of the three-phase AC/AC transformer; S n: is the nominal power of the transformer; V n: is the nominal voltage of the transformer on the low side; f n: is the working frequency; f res: is the resonant frequency of the L 1 CL 2 filter. • at least one power module for converting a DC input voltage into a three-phase AC output voltage; • a three-phase AC/AC transformer (10', 10", 10′′′) for adapting the three-phase AC output voltage of the power module to the three-phase AC voltage of the AC grid, wherein the AC grid has, at the connection point, an inductance "L 2 "; wherein the three-phase AC/AC transformer (10', 10", 10′′′) comprises: ∘ at least one winding on the low voltage side connected to the power module; ∘ at least one winding on the grid side, which is a medium voltage side, connectable in series with the AC grid; wherein the winding on the low voltage side connected to the power module together with the winding on the grid side have an equivalent inductance "L 1 " and an equivalent impedance "X CC "; ∘ at least one winding on the low voltage side connected to the power module; ∘ at least one winding on the grid side, which is a medium voltage side, connectable in series with the AC grid; wherein the winding on the low voltage side connected to the power module together with the winding on the grid side have an equivalent inductance "L 1 " and an equivalent impedance "X CC "; • a capacitor "C", connected to the winding of the grid side of the three-phase AC/AC transformer (10', 10", 10′′′); • defining at least two different values of a Short Circuit Ratio "SCR" at the connection point; • obtaining corresponding values of the inductance "L 2 " of the AC grid at the connection point for each value of the Short Circuit Ratio "SCR" by means of the following formula: L 2 = V n 2 2 πf n ⋅ SCR ⋅ S n • calculating the equivalent inductance "L 1 " of the AC/AC transformer by means of the following formula: L 1 = X cc ⋅ V n 2 2 πf n ⋅ S n • setting a value for the resonant frequency f res of the L 1 CL 2 filter and calculating, for each value of the Short Circuit Ratio "SCR", a corresponding value of the capacitor "C" by means of the following formula: C = L 1 + L 2 L 1 ⋅ L 2 ⋅ 2 πf res 2 • selecting a value of the capacitor "C" between the minimum and maximum obtained values for the capacitor "C"; X CC: is the equivalent impedance of the windings of the three-phase AC/AC transformer; S n: is the nominal power of the transformer; V n: is the nominal voltage of the transformer on the low side; f n: is the working frequency; f res: is the resonant frequency of the L 1 CL 2 filter.