Steam boiler assembly, configured to heat water in order to generate steam, comprising: - at least two boilers (20,30), comprising walls that define an interior that is configured to hold the water; - a fuel heater, configured to heat the water in the at least two boilers (20,30) upon the burning of fuel, - an electric heater (35,36), configured to heat the water in the at least two boilers (20,30) with electric energy, - a feed water inlet, configured to feed water into the steam boiler assembly, - a steam outlet, configured to discharge steam from the steam boiler assembly, and - a controller, configured to control the fuel heater and the electric heater (35,36), wherein the at least two boilers (20, 30) comprise: - a water-tube boiler, which comprises the fuel heater, - an electrode boiler, which comprises the electric heater (35,36), wherein the water-tube boiler and the electrode boiler are arranged in a parallel configuration and are each configured to generate steam in parallel, and wherein the steam boiler assembly further comprises: - a steam drum, comprising walls that define an interior that is configured to hold water and steam, wherein the controller is configured to selectively activate or deactivate the fuel heater and/or the electric heater (35,36) to bring and keep the water in the at least two boilers (20,30) at saturated conditions, wherein the feed water inlet and the steam outlet are fluidly connected to the steam drum, wherein the water-tube boiler and the electrode boiler each comprise an inlet (21,31), which is fluidly connected to the steam drum and which is adapted to allow the entrance of water from the steam drum into the respective boiler (20,30), wherein the water-tube boiler and the electrode boiler each comprise an outlet (22,32), which is fluidly connected to the steam drum and which is adapted to allow the exit of steam from the respective boiler (20,30) into the steam drum, and wherein the inlet of the water-tube boiler is fluidly connected to the inlet of the electrode boiler and wherein the interconnected inlets (21, 31) are configured to allow a flow of water from an activated one of the water-tube boiler or the electrode boiler to a deactivated one of the water-tube boiler or the electrode boiler in order to keep the water in the deactivated boiler at saturated conditions. - at least two boilers (20,30), comprising walls that define an interior that is configured to hold the water; - a fuel heater, configured to heat the water in the at least two boilers (20,30) upon the burning of fuel, - an electric heater (35,36), configured to heat the water in the at least two boilers (20,30) with electric energy, - a feed water inlet, configured to feed water into the steam boiler assembly, - a steam outlet, configured to discharge steam from the steam boiler assembly, and - a controller, configured to control the fuel heater and the electric heater (35,36), wherein the at least two boilers (20, 30) comprise: - a water-tube boiler, which comprises the fuel heater, - an electrode boiler, which comprises the electric heater (35,36), wherein the water-tube boiler and the electrode boiler are arranged in a parallel configuration and are each configured to generate steam in parallel, and wherein the steam boiler assembly further comprises: - a steam drum, comprising walls that define an interior that is configured to hold water and steam, - a steam drum, comprising walls that define an interior that is configured to hold water and steam, wherein the controller is configured to selectively activate or deactivate the fuel heater and/or the electric heater (35,36) to bring and keep the water in the at least two boilers (20,30) at saturated conditions, wherein the feed water inlet and the steam outlet are fluidly connected to the steam drum, wherein the water-tube boiler and the electrode boiler each comprise an inlet (21,31), which is fluidly connected to the steam drum and which is adapted to allow the entrance of water from the steam drum into the respective boiler (20,30), wherein the water-tube boiler and the electrode boiler each comprise an outlet (22,32), which is fluidly connected to the steam drum and which is adapted to allow the exit of steam from the respective boiler (20,30) into the steam drum, and wherein the inlet of the water-tube boiler is fluidly connected to the inlet of the electrode boiler and wherein the interconnected inlets (21, 31) are configured to allow a flow of water from an activated one of the water-tube boiler or the electrode boiler to a deactivated one of the water-tube boiler or the electrode boiler in order to keep the water in the deactivated boiler at saturated conditions.