A system for storage and dosing of ammonia includes solid ammonia storage material capable of binding and releasing ammonia reversibly by adsorption/absorption. The system includes a start-up storage unit and a main storage unit, both of which hold ammonia storage material. A start-up heating device is arranged to heat the start-up storage unit to generate gaseous ammonia by thermal desorption from the solid storage material. A main heating device arranged to heat the main storage unit to generate gaseous ammonia by thermal desorption from the solid storage material. A controller modulates operation of the heating devices such that the main and start-up heating devices are not simultaneously activated.