A system for storage and dosing of ammonia, including a solid ammonia storage material capable of binding and releasing ammonia reversibly by adsorption/absorption. The system is able to release ammonia gradually according to a demand that can vary over time with intermediate periods of no ammonia demand. A main storage unit and a start-up storage unit are provided. The storage units hold ammonia storage material. At least one one-way valve is provided via which the one main storage unit is in communication with the start-up storage unit. The one-way valve prevents any back-flow of ammonia from the start-up storage unit to the main storage unit. Heating devices are arranged to heat the main storage unit and the start-up storage unit separately to generate gaseous ammonia by thermal desorption from the solid storage material. A controller controls the heating power of the main storage unit and the start-up storage unit, thereby enabling ammonia release from at least one of the start-up and/or the main storage unit. A dosing valve controls ammonia flow from the storage units according to a demand.