Power-to-X (PtX) technologies are very important in renewable-based energy systems because of their capability to furnish a practical way for converting additional electrical energy from renewable sources into storable energy carriers such as hydrogen, ammonia and methanol. At the same time, grid connected PtX facilities rely heavily on power-electronic conversion stages, which makes harmonic distortion an important challenge for maintaining power quality and ensuring compliance with grid requirements. In such facilities, harmonic mitigation is commonly addressed by employing passive filters designed to attenuate selected harmonic components under defined operating conditions. Although passive filters can provide satisfactory performance for a given system configuration, the increasing penetration of renewable generation, the addition of new nonlinear converter-based loads and the resulting operating variations and uncertainties make it difficult for passive filtering alone to ensure effective harmonic mitigation under all operating conditions. In this context, a more practical solution is to retain the existing passive filter and complement it with the reduced-size shunt active harmonic filter thereby forming a hybrid passive–active filtering structure with improved flexibility and cost-effectiveness. This paper investigates such a hybrid filtering solution for grid-connected power-to-hydrogen systems. This paper investigates such a hybrid filtering solution for grid-connected power-to-hydrogen systems. The coordinated operation of the passive filter and the shunt active harmonic filter is evaluated under different operating conditions. Harmonic extraction strategies are developed and analyzed. The obtained results show that the suggested approach provides strong harmonic attenuation in the discrete-time environment and enables harmonic emission at the system level to remain below the specified grid requirements. The results indicate that hybrid passive–active harmonic filtering can provide a practical and cost-effective pathway for strengthening harmonic mitigation in renewable-based PtX facilities without replacing the existing passive filter structure.