Production of green electrical energy and green natural gas are the main goals of zero-carbon emission policy. Power to Gas plants (P2G) can be used to overcome difficulties with increase in intermittent renewable energy production, gas shortages and organic waste management. In this paper, a design, a model, and a control system for a Power to Gas plant is proposed. To achieve a high performance P2G plant, its design is based on biochar gasification and biological methanation processes. With the given mathematical models of electrolysis, gasification and methanation, calculation of needed feedstock and energy consumption as well as calculation of produced methane becomes easy obtainable. Proposed control system enables to precisely follow frequent operation change requests due to dynamical conditions in leaned electricity or gas grids. Simulation study of the automated plant operation using Matlab/Simulink has been done. This research gives all prerequisites for optimal sizing and planning of the P2G plant operation in dynamic technical and economic conditions.