Abstract: Demand-based closed-loop control is used in an electrochemical plant that has modules and a control unit, with each module being individually controlled by the control unit and supplied with a module-specific electric operating current. For each module to generate a separate product flow, product flows of the individual modules, connected in parallel, are merged to form a total product flow. When a start condition occurs, the control unit records a current total product flow demand, records a current efficiency of the modules based on a ratio of respective operating current and product flow, determines operationally ready modules, determines module-specific target operating currents for the operationally ready modules to cover the demand from a range of permissible module-specific target operating currents based on the efficiency of the modules and the demand, and sets the operating currents of the operationally ready modules to the determined module-specific target operating currents.